NO160966B - PROCEDURE FOR PREPARING A SMOKE-COLORED FOOD PRODUCT. - Google Patents

Description

The present invention relates to a method for producing a smoke-coloured food product where a tubular food casing is provided with a coating of low-tar liquid smoke which is produced from a tar-containing liquid smoke.

Tubular product casings made of cellulose are used extensively

to process a variety of meat products and other foodstuffs. The food casings are generally thin-walled tubes of various diameters, made from reconstituted materials such as regenerated cellulose. Food casings made of cellulose can also be produced with a fibrous net embedded in the wall, such casings are usually referred to as "fibrous food casings".

The different recipes and methods used to process food products in the food industry to satisfy varying tastes and also regional preferences usually make it necessary to use food casings with a number of different properties. In some cases, for example, casings are required that have multiple uses, casings that serve as containers during the processing of the food product that is enclosed by casings or also serve as a protective casing for the final product. However, the industry that manufactures finished meat products uses the food casings for the manufacture of many types of meat products, for example different types of sausages, frankfurters, bologna sausages, meat rolls, hams and the like, and the casing is often removed from the final product before it is cut up or before final packaging.

Surface appearance and taste are important factors for commercial

and consumer approval of the finished meat products,

and a common side of most types of such products includes the use of "smoking" to give the product a characteristic taste and colour. The "smoking" of the products is usually achieved by the manufacturer by subjecting the food product to actual contact with smoke in gaseous or cloud-like form. Such "smoke"-

however, processes have not been considered completely satisfactory for a number of reasons, including lack of efficiency and lack of homogeneity. Because of these shortcomings, many meat producers now use various types of liquid aqueous solutions of wood smoke components, commonly called "liquid smoke solutions", which have been developed and are used commercially by the food manufacturer to process many types of meat and other products. For the sake of convenience, "liquid smoke solution" as it is purchased will often be referred to as liquid smoke.

Application of "liquid smoke solution" to meat products is usually carried out in a number of ways, including spraying or dipping the food into the casing during its processing, or by adding "liquid smoke solution" to the recipe itself. The actual execution of the "smoking" by spraying or dipping is not completely satisfactory due to the inability to treat the product in the case evenly, and the addition of "liquid smoking solutions" in the meat recipe does not always give the desired surface due to dilution of the smoke components . Additions to the recipe also reduce the stability of the meat emulsion and will negatively affect the taste if large concentrations are used. Supply of liquid smoke to the food product in the casing of the food product, for example by spraying or immersion, also causes unexpected contamination and corrosion of the equipment. In addition, sausages in casings that have been treated with liquid smoke by commercial processing, after peeling the casing from the treated food product, will turn out to produce sausages that do not have a uniform smoke color from sausage to sausage, and from one load of sausages to another. What is even more undesirable is the lack of uniformity in color that can often be detected on the surface of the same sausage, including light and dark streaks, light and dark spots, and even uncolored spots that especially appear at the end of the sausage.

It is also claimed, for example, in US-PS 3,330,669

(Hollenbeck) that supplying a viscous, liquid smoke solution to the inner surface of a tubular food casing that has been stretched immediately before stuffing the casing with sausage emulsion leads to food products that have an acceptable color and smoky taste after cooking and removal of the holster. However, the Hollenbeck method has not proven to be practical and is not used there commercially. The viscous liquid smoke solution described in the patent is not practical for coating a casing on a high-speed production line to produce a coated casing which can then be conventionally crimped and used as a crimped casing on an automatic stuffing machine. The high viscosity of the solution limits the coating rate of the casing and, if a conventional method such as "plugging", also called "bubble coating", is used to coat the inside of the casing, the viscous Hollenbeck coating will necessitate frequent cutting of the casing for to renew the plug with the coating material in the casing, which leads to short casing lengths, and makes continuous creasing impractical.

It has now been shown that casings can be produced which can give special treatment or structural properties to the food products in a homogeneous and economical way by the casing manufacturer. This is especially true with the rise in connection with the development and extensive commercial use of automatic stuffing and processing equipment in the food industry.

Several methods for producing food casings with coatings applied to the surface are known and described in the patent literature. In US-PS 3 451 827, for example, a spraying method is described for applying a variety of coating materials to the inner surface of casings with a small diameter. In US PS

3,378,379 (Shiner) a "plug" method is used to apply coating materials to the inner surface of large diameter casings. While such and other methods have been used to produce commercial quantities of a variety of coated food casings, including casings where liquid smoke is used as a component of the coating preparation, the casings produced in this way are intended to meet special commercial requirements, and, insofar as it is understood, none of the previously known coated casings have been successfully demonstrated to impart a satisfactory level of "smoke", flavor and color to the meat products processed therein. For example, US-PS 3,360,383, 3,383,223 and 3,617,312 (Rose) describe coating preparations with different protein materials such as gelatin, which use liquid smoke solutions in quantities that are specifically required to insolubilize the protein materials. Such coated casings are said to have special adhesion properties necessary for processing dry sausages, and these properties are such that they will limit their applicability in many other applications.

Previous patents describe the application of liquid smoke to the inner surface of the casing, but attempts to internally coat the casing during manufacture have proven to be costly and speed limiting for high speed continuous production lines.

A solution to this problem comprises, as described in US-PS 4,118,619, treatment of the outer surface of the food casing with a liquid smoke preparation from natural wood. It has also been found that when the food casing is cellulose and made from either non-fibrous gel or fibrous gel, the use of highly acidic (pH value 2.0 - 2.5) aqueous liquid fumes will result in the formation a tar-like coating that accumulates on the carrier rollers and pinch rollers in the fume treatment unit, which eventually requires shutting down the treatment system.

The present invention aims to improve the known technique and thus relates to a method of the type mentioned at the outset, and this method is characterized by the liquid smoke being applied to a casing surface in a sufficient amount to give an absorbent index of at least approx. 0.2, preferably 0.3, at 340 nm wavelength, where said tar-poor, liquid smoke coating gives a casing extract with an absorbance at 210 nm wavelength that does not. is more than approx. 605É of the absorbance of a corresponding extract from an identical casing, with a comparable coating of said tarry liquid smoke sufficient to provide substantially the same absorbent index as said tubular food casings treated with tarry liquid smoke; stuffing casings treated with liquid smoke with foodstuffs, and treating the foodstuff in casings treated with liquid smoke under conditions sufficient to convert said foodstuff into an edible food product and form smoke color on the surface of the resulting food product.

In a preferred food casing produced according to the invention, treated with low-tar liquid smoke, the casing is of the "gel" type which will be explained in detail below, and it is made of cellulose without fiber reinforcement. The casing has a coating of low-tar liquid smoke which is formed from a liquid smoke containing tar with a total acid content of at least 10 wt-5é, and which is applied to a casing surface in sufficient quantity to give an absorbent index of at least 0, 2 at 340 nm wavelength, and a haze value that is not greater than the haze value of an identical casing without a coating of liquid smoke. As explained below, "total acid content" is a qualitative measure of the staining ability of both tar-containing liquid smoke and tar-deficient liquid smoke produced from tar-containing smoke. As explained below, "fog value" is a measure of the tar content of non-fibrous gel casings with a coating of low-tar liquid smoke produced from tarry liquid smoke with a total acid content of at least 10 wt.

The smoke preparation used in the manufacture of casings is a tar-poor, aqueous liquid smoke preparation with smoke colour, smell and taste with an absorptive capacity (defined below) of at least 0.15, and preferably at least 0.25, at 340 nm wavelength, and with a light transmission of at least 50#. As will be explained below, "absorbency" is a measure of the color ability of the liquid smoke, and "light transmission" is a measure of the tar content of the liquid smoke. As used herein, "light transmission" in an aqueous liquid smoke refers to the the latter's internal light transmission without the addition of materials that significantly affect the light transmission.The smoke preparation is described in more detail in NO-PS

The tar-poor, liquid smoke can be produced using several methods. Suitable methods are described in US-PS 4,518,619, 4,431,032 or 4,431,033.

The invention shall be described in more detail with reference to the figures, where: Figure 1 is a schematic sketch of an apparatus suitable for treating an outer surface of a food casing with tar-poor, liquid smoke in accordance with an embodiment of the invention; Figure 2 is a schematic sketch of an apparatus corresponding to the apparatus of Figure 1 and performing the same functions, but with low-tar liquid smoke to a desired moisture content while dissolved; Figure 3 is a schematic sketch of an apparatus corresponding to the apparatus of Figure 2, performing the same function, but having means for partially drying casings treated with low-tar liquid smoke in a flat state; Figure 4 is a graph showing the staining ability of a tar-poor, liquid smoke as a function of the temperature at the partial neutralization; Figure 5 is a graph showing ultraviolet absorption and ultraviolet transmission at various wavelengths, both for commercial "Charsol C-12" liquid smoke per se and the low-tar liquid smoke produced therefrom; Figure 6 is a graph showing ultraviolet absorption and ultraviolet transmission at various wavelengths, both for "Royal Smoke AA" liquid smoke per se, and the low-tar liquid smoke produced therefrom; Figure 7 is a graph showing ultraviolet absorption and ultraviolet transmission at various wavelengths, both for "Royal Smoke B" liquid smoke per se, and low-tar liquid smoke produced therefrom; Figure 8 is a graph showing the ultraviolet absorbent index load in the food casing as a function of low-tar liquid smoke; Figure 9 is a curve showing the percentage of non-volatile substances (including tars) in liquid smoke as a function of percentage light transmission.

Food casings that are suitable for the purpose of the invention are tubular casings, especially tubular casings, made of cellulose, which are produced in a manner known per se. Such casings are usually flexible, thin-walled, seamless tubes made of regenerated cellulose, cellulose ethers such as hydroxyethyl cellulose and the like with varying diameters. Tubular cellulose casings with fibrous reinforcement embedded in the wall, which are usually called "fibrous food casings", but also cellulose casings without fibrous reinforcement, which are called below "non-fibrous cellulose casings", can be used.

Cases which are usually referred to as "dry-stored cases" can be used. Such casings typically have a water content in the range of 5 to 14 wt-56 of water in non-fibrous casings or within the range of 3 to 8 wt-# of water in fibrous casings, based on the total weight of casing including water.

Sleeves that are usually referred to as "gel sleeves" are sleeves that have a higher moisture content as they have not been dried beforehand, and such sleeves can also be used. Gel casings are the type that give the aforementioned tar problems when treated with liquid smoke per se, whether they are fibrous or not.

Smoke colour, taste and smell components which are suitable for use are usually those referred to as colour, taste and smell components in liquid smoke per se.

The term "dissolution" as used herein means homogeneous,

true solutions, emulsions, colloidal suspensions and the like.

Liquid smoke is often a solution of natural wood smoke constituents, produced by burning wood, such as hickory or maple, and capturing the natural smoke constituents in a liquid medium such as water. Optionally, liquid smoke can be produced from the decomposing distillation of wood, i.e. the breakdown or cracking of wood fibers into various components that are distilled from the charcoal residues. Aqueous, liquid smoke is usually very acidic and has a pH value in the range of 2.5 and less, and a titratable acidity of at least 3 wt-#.

As used herein, the term "smoke color and smoke flavor components" refers to smoke color and flavor components that are produced from liquid smoke solutions in their commercially available form.

The tar-poor, liquid smoke used is made from natural wood smoke components. The source of liquid smoke is usually produced by a limited burning of hardwood, and the absorption of the smoke in an aqueous solution under control

learned conditions. The limited burning retains some of the unwanted hydrocarbon compounds or tars in insoluble form and allows the removal of these constituents from the final liquid smoke. In this method, the wood components that were previously considered desirable for the production of liquid smoke are absorbed in a solution in balanced proportions, and the unwanted components can be removed.

The resulting liquid smoke solution still contains

a significant proportion of tar, as producers and users of liquid smoke regard the dark-coloured tars as necessary to give the food a smoky color and flavour. The resulting liquid smoke is representative of the full range of wood smoke colors and flavors available. Table A summarizes several commercially available, liquid wood smoke preparations which contain tar with several properties which are considered important for the purposes of the invention. (This is discussed below-

for.) Apparatus and method for producing typical liquid smoke of the preferred type is most closely described in US-PS 3,106,473 (Hollenbeck) and 3,873,741 (Melcer).

As used here, the expression "at least partially neutral

cert" liquid smoke preparations with a pH value above about 4, and preferably from 5 to about 9, most preferably to a pH value in the range from 5 to 6.

It has been shown that commercially available liquid smoke is usually very acidic and that, as mentioned above, this can affect the peelability of the casing if a peeling agent such as carboxymethyl cellulose is used. To avoid this problem, a tar-poor and at least partially neutralized liquid smoke can be used according to the invention.

The low-tar liquid smoke can be applied to the outer surface of the tubular casing by passing the casing through a bath of low-tar liquid smoke. The liquid smoke is allowed to soak into the casing before excess is removed by passing the casing through pressure rollers or wipers or the like, and the time is sufficient for the casing to absorb the desired amount of smoke color and smoke flavor components.

The process of passing the casing through a treatment bath which is also referred to as a "deep bath" or a "dip tank" may also be referred to as the "dip" step. The tar-poor, liquid smoke can optionally be applied to the outside of the casing. In other methods such as spraying, brushing, rolling or the like.

Optionally, the tar-poor, liquid smoke can be applied to the inner surface of the casing by known methods which are described in US-PS 4,171,381 (Chiu). This includes plugging or bubble laying, spraying and coating during creasing. The plug method for coating the inside of the casing, involves filling a part of the casing with the coating material so that the plug of the coating material stays at the bottom of a "U" formed by the casing which is placed over two parallel rollers after which the continuous, indefinite length casing is moved, so that the plug of the coating material stays within the casing, while the casing moves past the plug, and is coated on the inside by the coating material found in the plug.

It can then be wrinkled by known methods or it can be dried and/or moistened to a water content suitable for wrinkling and/or further processing. The need for conventional drying and/or moistening after the preferably external treatment of tar-poor liquid smoke varies with the water content in the casing after the treatment and the casing type. If the casing is a non-fibrous casing, a water content in the range of 8 to 18 wt-# immediately prior to wrinkling is typical, and for fibrous casings, a water content in the range of 11 to 35 wt-56 water immediately prior to wrinkling is typical, where the percentage is based on the total weight of the casing including water.

A method of treating casings to obtain low-tar liquid smoke is shown in Figure 1. In Figure 1, a flat tubular sausage casing of cellulose 10 is treated on the outside with a low-tar liquid smoke preparation during the passage over lower and upper guide rollers 13 through a dip tank 11, which contains the tar-poor, liquid smoke preparation 12. The casing passes over lower and upper guide rollers 14 after the outlet of the dip tank, and is then passed between the pressure rollers 20 which reduce an excess of entrained liquid. The total contact time for the casing 10 with tar-poor liquid smoke preparation 12 in the dip tank 11, and with excess liquid smoke preparation in the casing that passes over the guide rollers 14 before the casing passes through the press rollers 20, will determine the amount of smoke color and flavor from the tar-poor liquid smoke preparation that the holster will entail. The total contact time is measured from point A to point B in figure 1. After the casing passes through the pressure rollers 20, it passes over the guide roller 23 and is wound up on the drum 24. The casing is then sent for further, conventional treatment, for example conventional moistening which possibly requires and regular wrinkling.

The embodiment shown in Figure 2 differs from that shown in Figure 1 in that the casing, after passing through the press rollers 20 in Figure 2, is led into a heating and drying chamber 21 where it is dried to a suitable moisture content. The casing is inflated with an air bubble which is held in a relatively fixed position between the press rollers 20 and 22, by the sealing action of the rollers 20 and 22. The heating chamber 21 can be any device, for example a hot air circulation chamber which dries the sausage casing to a suitable moisture content . After the casing exits the heating chamber 21 and through the press rollers 22, it passes over the guide roller 23 and is wound up on the drum 24. The casing is then sent for normal further processing, which includes conventional moistening that may be necessary and normal creasing.

The design shown in Figure 3 differs from that shown in Figure 2 in that the sleeve in Figure 3 is dried in a flat state while passing over the guide roller 25.

It should be noted that the low-tar liquid smoke that is coated on the casing surface either on the outside or inside does not exist only as a surface coating. Smoke colour, odor and flavor components that are coated on the surface penetrate the cellulose structure in the casing, and the cellulose absorbs the moisture in the smoke solution. Examination of the cross-section of the case wall reveals a color gradient across the case wall, with the smoke-colored surface having a darker color than the surface on the opposite side of the case. As used herein, the term "coating" shall mean that the casing wall is not only coated with smoke components, but the casing wall is also Impregnated with smoke components.

The low-tar, liquid smoke may also contain other components suitable for treating tubular food casings to which the smoke components are applied, for example glycerol and/or propylene glycol which can be used as wetting or softening agents or the like.

Other components that are normally used for the production or further processing of food casings, for example cellulose wood and mineral oil, can also be present in the casing if this is desired, and they can also be used in the same way and in the same quantities as if low-tar, liquid smoke had not been used. used.

In particular, agents for improving the peelability of the casings from food products such as sausages, for example frankfurters, bologna sausages and the like, may optionally be applied to the inner surface of the casing before or after the external application of tar-poor, liquid smoke to the casing and before or during wrinkling. If the low-tar liquid smoke is applied to the inner surface of the casing, preferably the peel agent is applied first. Such agents that increase peelability include, but are not limited to, carboxymethyl cellulose and other water-soluble cellulose ethers, the use of which is described in US-PS 3,898,348 (Chiu); "Aquapel" a product consisting of alkyl ketene dimers and the use of which is described in US-PS 3,905,397 (Chiu); and "Ouilon", a product consisting of fatty acid chromyl chlorides and the use of which is described in US-PS

2,901,358 (Underwood).

Agents that increase peelability can be applied to the inner surface of the casing using one of a number of known methods. For example, the agent which increases peelability can be supplied to tubular casings in the form of a "plug" of liquid corresponding to US-PS 3,378,379 (Shiner). Advancing the casing past the floating plug coats the inner surface. Optionally, the agent which increases peelability can be applied to said surface of the casing through a hollow mandrel over which the casing is advanced, for example a mandrel in a wrinkle machine in a manner similar to that described in US-PS

3,451,827 (Bridgeford).

A sleeve with printing can also be produced, for example a sleeve with a brand, trademark, letters and the like printed on it, with smoke color and smoke flavor components added to the sleeve. Examples of printed casings are described in US-PS 3 316 189.

The casing is also suitable for processing what are usually called "dry sausages". Different from other types of non-fibrous and fibrous casings which are preferably easy to peel from the product, either by the food manufacturer before sale to the consumer or by the consumer, the casing for "dry sausages" will be bound to the food product during and after processing. "Kymene", a polyamide epichloridine resin, the use of which is described in US-PS 3,378,379, may optionally be applied to the inside of a casing that is internally treated with a low-tar liquid smoke to improve the binding of casings to the food products being processed in the casing.

The following examples are illustrative. Unless otherwise noted, all parts and percentages are parts by weight and pounds by weight, and all percentages relating to casings are based on the total weight of the casing.

Example I

This example shows the production of a low-tar, liquid smoke preparation by the solvent extraction method. To 1.8 L of methylene chloride is added 18 L of liquid smoke preparation per se "A" ("Royal Smoke AA" with an absorbance of 0.6 at 340 nm), and the liquids are thoroughly mixed by inverting the container. The methylene chloride containing the tars was separated from the liquid smoke by gravity, that is, the tar-rich methylene chloride layer at the bottom was drained off until the upper layer of tar-poor, liquid smoke was as it appeared by visual observation. The resulting liquid smoke preparation was substantially tar-free as determined by a qualitative water compatibility test in which a sample of liquid smoke was mixed with water and observed for tar precipitation or lack thereof. The pH of a portion of the aqueous liquid smoke was then adjusted to 5.0 by adding a sufficient amount of 50% NaOH solution to the smoke solution. The pH value in a sample of liquid smoke per se was similarly adjusted to 5.0. The chemical composition of the four liquid smoke solutions used in this example is shown in table B.

Table B shows that tar-poor, liquid smoke preparation produced by the solvent extraction method has a significantly different chemical character from tar-containing, aqueous liquid smoke per se. On a weight basis, the reduced tar preparations in table B (samples B2 and B4) have less than approx. half the phenolic content of the tarry liquid smoke preparation from which they are prepared (Sample B^), and this represents a preferred preparation". While the data in Table B show that the extraction significantly changes the total acid level and carbonyl concentration, other pressing work suggests that one does not can draw some conclusion as to the effect of the extraction on the total acid content or the carbonyl concentration. While the tar-poor liquid smoke has a significantly lower concentration of phenolic components than the tar-containing liquid smoke solution from which it is prepared, the protein stain-forming ability of the former is not (colour development) and the natural smell and taste properties significantly reduced, as is evident from the following examples.

It is also clear from a visual examination of the samples in table B that these samples relating to the invention contain significantly less tar with a high molecular weight, they are significantly lighter in colour. In addition, they are totally miscible with water.

The procedure for determining the total acid content is described below. The procedure for determining the content of phenol and carbonyl in liquid smoke follows.

All samples are filtered through a Whatman No. 2 filter paper or equivalent and cooled on receipt or on preparation until the time of analysis to avoid possible polymerisation. Distilled water is used for all dilutions. The samples are diluted with water in two steps, starting with a 10 ml amount. In the first step, the dilution is up to a total volume of 200, and in the second step, 10 ml of the first solution is further diluted to a total volume of 100 ml. For phenol determination, 5 ml of the second solution is further diluted, third step with distilled water to a total volume of 100 ml. For carbonyl determination, 1 ml of the second solution is further diluted with carbonyl-free methanol to a total volume of 10 ml.

For the phenol determination, the reagents are:

1. Boric acid-potassium chloride buffer pH 8.3. Dilute the indicated quantities of solution to 1 1 water.

0.4M boric acid - 125 ml

0.4M potassium chloride - 125 ml

0.2M sodium hydroxide - 40 ml

2. 0.6* NaOH

3. Color reagent: N-2,6-trichloro-p-benzoquinonimine stock solution: Dissolve

0.25 g in 30 ml of methanol and keep the solution in a refrigerator.

4. 2,5-dimethoxyphenol standards.

Prepare solutions of 1 to 7 jjg/ml DMP in water for standard curve.

This method for phenol determination is a modified Gibbs method, based on the method described in Tucker, I-W. "Estimation of Phenols in Meat and Fat", JCAC, XXV, 799

(1942), where the reagents are mixed together in the following order:

1. - 5 ml pH 8.3 buffer.

2. -5 ml of a dilution of unknown diluted liquid smoke and standard 2,6-dimethoxyphenol solution, or 5

ml water for blank test.

3. - Adjust the pH to 9.8 using 1 ml of 0.b% NaOH.

4. - Dilute 1 ml of color reagent stock solution to 15 ml in water. Add 1 ml of diluted color reagent. Produced

just before addition.

5. - Let the color develop for exactly 25 minutes at room temperature. 6. - Determine absorption at wavelength 580 nm in a 1 cm colometer tube with a "Spectronic 20" or equivalent. 7. - Prepare a standard curve using absorption as abscissa and standard concentrations as ordinate. Extrapolate concentration of DMF in liquid

smoke resolution from this curve.

8. - Calculate mg/DMP liquid smoke using the following equation:

To calculate mg DMP/g liquid smoke, divide the result from the equation above by the weight (g) of 1 ml of liquid smoke.

For the carbonyl determination, the reagents are:

1. - Carbonyl-free methanol. 5 g of 2,4-dinitrophenylhydrazine and a few drops of concentrated HCl are added to 500 ml of methanol.

Boil under reflux for 1 3 hours and distil.

2. - 2,4-dinitrophenylhydrazine solution.

Prepare saturated solution in carbonyl-free methanol using twice recrystallized product. Saved

refrigerated and prepared fresh every two weeks.

3. - KOH solution. 10 g in 20 ml distilled H 2 O diluted to 100 ml with carbonyl-free methanol. 4. - 2-butanone standard. Prepare solutions of 3-10 mg of 2-butanone in 100 ml of carbonyl-free methanol for a standard curve.

The method is a modified Lappan-Clark method, based on the method described in their article "Colorimetric Method for Determination of Traces of Carbonyl Compounds", "Anal. Chem." 23, 541-542 (1959). The procedure is as follows: 1. - Add 1 ml of diluted liquid smoke solution or 1 ml of standard butanone solution or 1 ml of methanol (for reagent blank) to 25 ml volumetric flasks containing 1 ml of 2,4-dinitrophenylhydrazine reagent

(preheated to ensure saturation).

2. - Add 0.05 mL of concentrated HC1 to all 25 mL bottles, mix the contents of each, and place in a water bath for 30

minutes at 50'C.

3. - Cool to room temperature and add 5 ml of KOH solution to each. 4. - Dilute the contents of each bottle to 25 ml with carbonyl-free methanol. 5. - Read 480 nm against the methanol blank, set to absorbance 0 (cuvettes - 0.5 x 4 (10.1 cm) or equivalent. Use "Spectronic 20" or equivalent. 6. - Plot absorbance against 2-butanone (MEK ) concentration in mg per 100 ml for standard curve 7. - Prepare a standard curve using absorption as abscissa and standard concentrations (mg MEK/100 ml) as ordinate.

Extrapolate the concentration of MEK in liquid smoke solutions from this curve. 8. - Calculate mg MEK/100 ml liquid smoke with the following equation: mg MEK (from std. curve) x dilution factor _ M/100 ml n> smoke loo mi .-ai

To calculate mg MEK/g liquid smoke, divide the result of the above equation by the weight (in g) of 100 ml of smoke.

Example II

This example shows the production of tar-poor, liquid smoke by controlled temperature neutralization. To 485 1 (445 ltg) of "Royal Smoke AA" liquid smoke per se containing tar with a pH value of 2.5 and an absorptivity (defined below) of 0.65 at 340 nm wavelength, 33 kg of NaOH flakes are added in a quantity of 0.9 kg/minute. The vessel was stirred continuously and cooled with a chilled jacket of brine. The temperature varied in the range of 14 to 17°C during the treatment. At the completion of partial neutralization to a pH of 6.0, stirring was stopped and the tar allowed to settle overnight. The tar precipitate and the tar-poor supernatant were separated, and the latter was further filtered through a submicron filter cartridge. The resulting liquid was largely tar-free as. determined by a qualitative water solubility test and liquid fumes were formed with water and observed for tar precipitation or lack thereof. There was no visible precipitation of tar. The chemical composition of liquid smoke per se and tar-poor liquid smoke in the example is shown in table C.

Table C shows that tar-poor, liquid smoke preparations, produced by controlled temperature neutralization, have a chemical character that is significantly different from the character of tar-containing, watery, liquid smoke as purchased. It will be noted that the phenol content is substantially reduced, but the carbonyl content and the total acid content in the tar-poor liquid smoke are apparently higher than the corresponding values for the original tar-containing liquid smoke. As noted in the discussion with respect to Table B, other test work suggests that no conclusion can be drawn from the experiments regarding the effect of controlled temperature neutralization on total acid content or carbonyl concentration. A possible explanation is that components such as acids, which are very volatile in the free state (pH 2), but not volatile in salt water, can be partially lost in the analytical procedure, where the preparation of the sample includes distillation and recovery.

Although the tar-poor liquid smoke in Examples I and II was separated from the heavier tar fraction in a single step by natural settling, other separation methods can be used. For example, multi-stage contact between two liquids in the solvent extraction method can be carried out at room temperature and normal pressure, or by heating and elevated pressure. The natural precipitation can also be accelerated by mechanical devices such as liquid-liquid cyclones or centrifugal devices. Multi-stage extractions can be used by using a number of such devices or by using a vertical counter-current column. Suitable counterflow columns include spray towers, packed columns, tray columns containing perforated trays or modified bubble trays, and internally stirred columns such as rotating disc columns.

Example III

This example shows the tar problem when liquid smoke per se is supplied to tubular gel food casings and the elimination of the problem by using low-tar liquid smoke.

A non-fibrous cellulose frankfurter casing made from gelware was taken from the casing manufacturer's process at a point prior to the normal drying step. This wet casing was passed through a dip tank containing liquid smoke solution ("Royal Smoke AR") per se. As the case was passed through the dip tank, a dark tar-like coating eventually began to settle on the outer case surface from the smoke solution as the smoke solution entered the case wall. As the process continued, the tar coating transferred from the casing surface began to accumulate on the carrier rolls and the pressure roll in the fume treatment unit. This tar coating was sticky and eventually the treated casing began to bond to the rollers, and to accumulate on the rollers and then break. Treatment was discontinued.

A second treatment was started using the same gel sleeve. A partially neutralized mixture was prepared by adding 8 g of anhydrous sodium carbonate to 100 g of "Royal Smoke AA" per se without temperature control of the solution. The latter was filtered to remove precipitated tars, and the remaining solution with a pH value of 5.6 was a tar-poor liquid smoke solution prepared by the neutralization method. This solution was transferred to a dip tank and the non-fibrous casing was passed through for low-tar liquid fume treatment of the outer surface. There was no significant tar formation either on the casing or the rollers.

The fumigated casing was then passed through a dryer in the inflated state under conditions sufficient to produce a non-fibrous frankfurter casing having a flat width of 3.3 cm. Samples of the casing were then plug treated in the laboratory with a solution to increase peelability containing 0.85# sodium carboxymethyl cellulose. This inner coating gave approx. 0.5 mg solution per cm<2> casing surface to improve the peeling properties of the casing.

The casing was then hand tamped in the laboratory with a protein emulsion. The product in the case was processed in a laboratory oven and the case was then peeled off to produce a final product with a uniform smoke color without rubbing off. No taste tests were done.

Example IV

This example illustrates the preparation of a tube-shaped food casing treated with low-tar smoke using liquid smoke prepared by the solvent extraction method as described in Example I. In addition to "Royal Smoke AA" as a starting material, the sample was prepared with "Charsol C-10" with an absorbent capacity of approx. 0.4 at 340 nm, and the latter is identified in Table D as smoke "C" per se and low-tar liquid smoke preparation "C".

Several non-fluid frankfurter gel casings were treated with neutralized (pH 5.0) liquid smoke preparation as prepared in Example I by applying liquid smoke solution to the outer surface of the casings. The liquid smoke addition was approx. 1.55 mg/cm<2> of the casing surface. The application device was a device which distributed the aqueous, liquid smoke solution evenly around the casings, and it consisted of two main parts: namely, a device for applying liquid smoke and a smoothing unit. The application unit consisted of a stationary foam disc mounted so that liquid smoke entered the outer rim. Small, flexible plastic tubes led the liquid to the center core through which the dissolved casing was passed. The foam disc bends according to the holster size and is suitable for a variety of holsters with different cross-sections. Because the supply of liquid smoke is not uniform, a rotary smoothing device was used immediately after the application station. It contained a rotating foam disc with a core size appropriate for the case size being treated. The disc was driven by an air motor with a speed of 200 to 250 revolutions per minute. minute. Excess liquid smoke from the application device and from the smoothing device was collected in a common vessel and returned to the inlet of the application device. The treated casing was passed through a system of point supports to and through a drying section. The aforementioned system for coating and guiding the casing is not part of the present invention.

The treated casings were dried at 80°C to a water content of 12% by weight. The casings were then conventionally wetted to 14-18 wt-# and crimped. The levels of the smoke preparations, the phenolics, the carbonyls and the total acid content of the treated casings are shown in Table D.

An embodiment of the low-tar smoke-colored and smoke-flavored casing according to the invention can be partially characterized as a casing with a low-tar smoke coating that has less than half the phenol content (on the basis of weight per unit area of treated casing surface) of a casing that is coated with a tar-containing, aqueous , liquid smoke preparation from which the tar-poor liquid smoke is produced. Table D shows specific examples where casings according to the invention, coated with low-tar, liquid smoke preparation A, only have 1/3 of the phenol content of casings treated with partially neutralized, tar-containing, liquid smoke solution A ("Royal Smoke AA", compare casing C± with casing CG). Similarly, casings coated with low-tar liquid smoke preparation B had less than 1/4 of the phenol content of tar-containing liquid smoke solution B ("Charsol C-10", comparison between casings C3 and C4). As in Table B, no conclusion can be drawn with respect to the effect of the invention on the carbonyl content or the total acid content of the casing. Due to the nature of these tests, the phenol reduction in liquid smoke (Table B) and the phenol reduction in the coated casing (Table D) are not proportional.

Example V

This example shows the production of a tubular sleeve, treated with tar-poor liquid smoke, according to the invention, using a liquid smoke produced by controlled temperature neutralization as described in example II. For comparison, the same casing (non-fibrous cellulose) was similarly treated with tarry "Royal Smoke AA" liquid smoke per se.

Frankfurter size casings, made from gel, were treated with liquid smoke preparations of Example II in an amount of about 1.55 mg/cm<2> when applied to the outer surfaces of the casings. Application device was the same as described in example IV.

The treated casings were dried at 80°C to a water content of 12 wt-56. The casings were conventionally moistened to 14-18 wt-# of water during wrinkling. The phenols, carbonyls and total acid content of the treated casings are shown in the table

E.

Due to the nature of these tests, the phenol reduction in liquid smoke (Table C) and the phenyl reduction in coated casings (Table E) are not proportional. As for Table C, no conclusion can be drawn with respect to the effect of the invention on the carbonyl content, or the total acid content of the casing. In relation to the total acid content, the higher level in the partially neutralized and tar-poor casing reflects the lower volatility in salt form of the acids at higher pH values. A possible explanation is that the acid components, which are very volatile in the free state (pH = 2), are not so volatile in salt form (pH = 6), and that they can be partially lost during drying of casings treated with liquid smoke per se.

Objective criteria are used to compare the protein staining (colour development) of aqueous, liquid smoke preparation with the tarry, liquid smoke from which it is produced. These criteria include "stain ability" as it appears from the liquid preparations themselves, and "stain index" which relates to the coating on the tubular food casings. In each case, the tested embodiments of the invention show a significant staining ability even if the tar content is reduced to a level such that the tar problems that have been experienced until now do not arise.

The procedure for measuring the staining ability and the staining index is as follows: The procedure is based on the reaction you get during meat processing where meat protein reacts with the smoke components so that you get the desired, dark smoke color on the products. To quantify this staining or darkening ability, unknown or recently smoke-treated casings are reacted with a specific amino acid (glycine) under acidic conditions at 70°C for 30 minutes. The absorbance of the solution is measured at 525 nm. This method can be used on liquid smoke or on casings treated with liquid smoke, and this with reproducible results. The detailed procedure is as follows: I. Prepare a 2.5# solution of glycine in 95$ acetic acid; (a) dissolve 12.5 g of glycine in 25 ml of water in a 500 ml volumetric flask. Add enough glacial acetic acid for total dissolution. (b) dilute to the indicated level with glacial acetic acid; II. In the case of liquid smoke analysis, weigh out 15-20 mg (± 0.1 mg) of the liquid smoke to be processed in a 15 ml test tube, or; III. When analyzing smoke-treated casings, prepare 4 double-thickness slices from the casing so that a total casing area of 12.9 cm<2> is obtained for 8 washers: (a) If casing is wrinkled, inflate one part with 0.7 atmospheres of air to smooth the surface. Compress the holster by pulling it over a hard surface. Cut out slices and add them to the test tube; IV. To the test tubes containing liquid smoke or treated casings, add 5.0 ml of 2.5% glycine/acetic acid solution. V. Cap the test tubes, shake by hand to ensure contact with the sample and place the tubes in a 70°C oven or constant temperature bath for 30 minutes; WE. Measure the absorbance at 525 nm for each solution using the glycine reagent as a blank; VII. The absorption is reproduced as spot-forming ability for liquid

smoke or stain index for smoke-treated casings.

The numerical value for the spot index is absorption per 12.9 cm<2> case surface.

The staining ability represents the ability of liquid smoke to develop a certain absorption or color during the procedure for the staining index, i.e. units of absorption per mg fluid.

Example VI

A series of tests was carried out where tarry liquid smoke per se was partially neutralized from an initial pH value of 2.3 to a final pH value of 6.0 under controlled temperature conditions, (controlled temperature neutralization), and also non- controlled temperature conditions (the neutralization method). Staining power was determined at various neutralization temperatures and data plotted in Figure 4 for "Royal Smoke AA" liquid smoke (upper curve) and "Charsol C-10" liquid smoke (lower curve).

More specifically, the liquid smoke per se used in each sample was partially neutralized by adding 50% NaOH with continuous mixing and cooling using a submerged portable cooling unit to remove heat in the solution, and to maintain the temperature of the mixture at the desired level. After a necessary amount of base had been added to reach the desired pH value of 6.0, the tar precipitate was separated by sedimentation and the tar-poor, supernatant liquid was used to measure the staining ability.

Examination of figure 4 shows that the staining ability in partially neutralized "Royal Smoke AA" remains relatively constant at approx. 0.027 in a controlled temperature range of 5-30"C, while the staining power of partially neutralized "Charsol C-10" liquid smoke remains largely constant at about 0.022 in the same temperature range. At higher temperatures, the staining power begins to decrease. For this particular test series and with uncontrolled temperature neutralization (no cooling), the maximum uncontrolled neutralization temperature was reached when the mixture was at about 60° C. This example illustrates that higher staining ability is obtained when producing low-tar liquid smoke by controlled temperature neutralization rather than by the uncontrolled temperature neutralization method.

Example VII

A series of ultraviolet absorption spectroscopy tests are performed using non-flammable cellulose food casings treated with low-tar liquid smoke and the casings treated with tar-containing liquid smoke per se. These samples demonstrate the essential difference between the two types of casings. The samples include three different types of liquid wood smoke: "Charsol C-12", "Royal Smoke AA" and "Royal Smoke B". These tarry liquid smoke preparations were applied to the outer surface of the casing in per se form at a pH value of 2.4 and also after tar removal by solvent extraction (pH 2.4), neutralization and controlled temperature neutralization (pH 6 ,0). The sheath had a diameter of 21 mm and was made of non-fibrous cellulose, and the coating was sprayed onto the outer surface to improve peelability. In this and subsequent examples, the improved peelability solution was of the type described in US-PS 3,898,348 (Chiu). The amount of application was 0.47-0.78 mg/cm<2> casing surface, and the range of preparations used in this solution is given in Table F. tar-poor liquid smoke preparations and tar-containing liquid smoke per se were each applied to the exterior of the casing in the same way as described in the previous examples, and in an amount of approx. 1.55 mg/cm<2> case surface.

The absorption spectrum in ultraviolet over 350 to 210 nm was recorded for liquid samples from the various smoke-treated casings by the following procedure: (a) A 0.0635 mm<2> sample of liquid smoke-treated casing was immersed in 200 ml of anhydrous methanol and then removed. (b) Depending on the amount of liquid smoke, further dilution must be done for compatibility with the UV equipment. In these cases, the addition of liquid smoke was approx. 1.55 mg/cm<2> casing, and solutions used for the measurement consisted of 4.96 ml of methanol and 0.10 ml of the extract from step (a). (c) The UV spectrum was recorded in the 350 to 210 nm range with the following format: 2 second response/2 mm slit, 10 nm/cm map, 50 nm/minute recording speed, and $0.200.

To measure the absorption due to the presence of tar in liquid smoke, the spectrophotometer was zeroed with an extract solution containing the lowest possible tar content. For a special type of liquid smoke, this was extracted and neutralized (pH 5.0) smoke-treated casing as an extract sample. 0-set in this way, a further absorption in the UV spectrum provides a quantitative measure of the tar components present.

The result of these tests for "Charsol C-12" is reproduced in Figure 5, where liquid smoke per se is shown as a solid line. The low-tar liquid smoke produced by the neutralization method is shown as a dashed line, the low-tar liquid smoke produced by controlled temperature neutralization is shown as a dash-dotted line, and the low-tar liquid smoke produced by the solvent extraction method is shown as is dotted line. The results for the ultraviolet absorption tests for "Royal Smoke AA" per se and "Royal Smoke B" per se, and for tar-poor liquid smoke from these, are similarly reproduced in Figures 6 and 7. The transmission greater than 0 which is reproduced in the curves in figures 5 to 7, is a function of the machine blind test used in these particular experiments.

Examination of the curves in Figures 5 to 7 shows that the greatest difference between tar-poor samples and tar-containing samples takes place at 210 nm wavelength, although there is a significant difference over the entire investigated range of wavelengths. The difference is greatest with liquid smoke with the highest total acidity and highest tar content ("Charsol C-12", "Royal Smoke AA"). The absorption difference is less with "Royal Smoke B", but lower total acidity and lower tar content, when treated with controlled temperature neutralization and the neutralization methods.

Absorption and percent light transmission at 210 nm wavelengths are reproduced in Table G, and can be used to show that the smoke extracts from cellulose casings treated with the described tar-poor liquid smoke have an absorption at 210 nm wavelength of no more than 60", and preferably no more than 30% of the ultraviolet absorption of the smoke extract from a similarly treated casing with tarry liquid smoke, at the same absorptive index (defined below). Table G also shows that the ultraviolet light transmission for cellulose casings treated with tarry liquid smoke according to NO- PS

at 210 nm wavelength, is at least four times the ultraviolet light transmission of an identical casing treated with tar-containing, liquid smoke from which the tar-poor dent is produced.

Example VIII

The non-fibrous cellulosic casings from gel according to the invention preferably have a coating of tar-poor, liquid smoke which leads to a haze value that is not more than 80$ of the haze value and preferably not more than 70$ of the haze value in the casing, which an identical casing has with a coating of a tarry, liquid smoke from which the tar-poor is made. The tarry liquid smoke has a total acid content of at least approx. 10 weight-$.

Haze value represents a measure of the tar content of the casing and this casing property was demonstrated in a series of experiments that included haze determination for non-fibrous cellulose gel casings without smoke treatment, with treatment with tarry liquid smoke per se and with treatment with tar-poor smoke. In each case the tarry liquid smoke was per se "Royal Smoke AA", with a total acid content of 11.5-12 wt-# (Table A). The general procedure was to immerse the casing in water and during this period any tar components in the casing wall are rendered insoluble by water. To the extent that tar is present, water compatibility can be quantitatively measured in the form of a cloud-like mist in the casing.

In the experiments, tar-poor liquid smoke produced by the solvent extraction method was first brought into contact with methylene chloride liquid in a volume ratio of 10:1 liquid smoke solution: liquid solvent. After mixing, the solution was left for 12-16 hours so that two layers are formed, and the tar-poor upper layer of liquid smoke was separated and partially neutralized to a pH value of 5.0, and added to the outer surface of the cellulose casing by the method in example IV. For all the liquid smoke treatments in this Example VIII, the liquid smoke was applied to the casing outer surface 1 in an amount of 1.55 mg/cm<2> casing surface.

The tar-poor liquid smoke produced by the neutralization method was partially neutralized by adding NaOH, without temperature control to liquid smoke per se, so that a pH value of 5.5 was obtained, and the tar-poor part was separated by decantation. This low-tar liquid smoke was supplied to the casing wall by applying the liquid smoke to the outer surface of the gel casing.

The tar-poor liquid smoke produced by controlled temperature neutralization was neutralized to a pH value of 6.0 at 10-15°C in the manner described in Example II. The tar-poor liquid smoke was separated from the tar precipitate and supplied to the casing wall by the method in example IV. For all of the casings used in this Example VIII, the improved peelability solution from Example F was sprayed onto the inner surface of the casing. The 21 mm diameter non-fibrous casings were wrinkled, and a 91.4 cm long sample was taken randomly from a wrinkled rod, inflated with air to reduce wrinkles, and immersed in 200 ml of delonized water. The immersion time was at least one hour, but no more than 3 hours, i.e. only sufficient for complete penetration of the casing wall by water. After the samples were dried, casing haze was measured using the general procedure described in ASTM Method D 1003, Volume 35, "Haze and Luminous Transmittance and Transparent Plastics" (1977). The results of these tests are reproduced in table H as follows:

Table H shows that casings treated with low-tar liquid smoke (made from "Royal Smoke AA") have haze values of (7.6, 6.7 and 6.6$) which are no more and in fact less than the haze value of an identical casing without coating of liquid smoke ($7.9).

The average haze value for different manufacturers' holsters can vary somewhat, although most holsters (without liquid smoke treatment) are in the 7.7-8.2$ range. However, the average haze value for untreated cellulose casing from one manufacturer is much higher, namely approx. 21.9$.

It will be recalled that using the haze value to characterize casings treated with tar-poor liquid smoke according to NO-PS 823407 is limited to casings that have been smoke-treated in a gel state. With this type of casing, the liquid smoke actually penetrates the casing wall and any tar components are made insoluble with water during the subsequent wetting. With dry casings treated with liquid smoke, the smoke apparently does not penetrate the outer surface and is washed off during the water treatment when measuring the haze value. Consequently, the haze value is not useful for characterizing dry-stored casings that have been treated with low-tar liquid smoke. As an illustration, there is no difference between dry casings treated with tarry and tarry "Royal Smoke AA" liquid smoke in an amount of approx. 1.55 mg/cm<2> case surface.

The haze value properties of gel casings treated with low-tar liquid smoke also require the use of liquid smoke with a total acid content of at least approx. 10 weight-$. Liquid smoke with a lower acid content obviously does not contain enough tar to produce a measurable difference in haze value between casings coated with tar-containing and tar-poor liquid smoke. "This is illustrated by samples involving case treatment with tarry and low-tar "Royal Smoke B" liquid smoke per se, added in an amount of 2.17 mg/cm<2 >case surface. "Royal Smoke B" has a total acid content of 68 .5-9.0 weight-$ (see table A), and there is no demonstrable difference in the haze value for the two types of casings.

It is obvious from table H that the average fog for the cellulose casing treated with tar-containing liquid smoke per se is significantly higher than the average fog for cellulose casing treated with tar-poor liquid smoke according to NO-PS823407. The highest average haze value of the three types of casings treated with low-tar liquid smoke ($7.6) is 71$ of the average haze value of casings treated with tar-rich liquid smoke per se, which is an upper limit of less than about. 80$: of the non-fibrous casings according to the invention, treated with low-tar liquid smoke. The other two types of casings have average haze values that are 62$ of the average haze value for casings treated with liquid smoke per se, illustrating that the most preferred upper limit of less than approx. 70$. Since the fog value varies somewhat from sample to sample, it is understood that the fog requirements for the casings according to the invention are based on the arithmetic mean of at least 10 samples.

Average fog values are also a function of casing diameter, increasing with increasing diameter due to the thicker casing wall. The absolute value of the average haze value further depends on the total acid content (and absorptive capacity discussed below), on the smoke in question, and the amount of smoke supplied to the casing. In general, however, the average haze value for the cellulose casings according to the invention is substantially lower than the average value for cellulose casings that have been treated with liquid smoke per se, even though their smoke color and smoke flavor-developing properties 1 the food products treated in the casings are approximately the same when they produced under similar conditions. This relationship shows that chemical and functional differences between cellulose casings treated with low-tar, liquid smoke and casings treated with liquid smoke per se.

The fog test is only useful for characterizing cellulose casings and not in fibrous casings according to the invention. This is because the fibrous casings themselves are opaque and have a very high average haze value, for example approx.

$97.50 for untreated fibrous casings with a diameter of 70 mm.

Example IX

The outer surfaces of frankfurter cellulose casings with a diameter of 21 mm were treated with low-tar liquid smoke produced by controlled temperature neutralization as 1 example II and used in the treatment 1 example V. For comparison, casings of the same size were not treated with liquid smoke, used with and without this solution to increase the peelability mentioned in Table F, sprayed on the inner surface of these control casings. All casings should be stuffed with either an emulsion of beef with a composition as in table I, or the meat recipe with a high collagen content in table J.

The stuffed casings were processed under normal temperature conditions practiced commercially, and mechanically peeled with commercial equipment. Two processing chambers were used for the two types of emulsions, but they were programmed in the same way to raise the temperature from 60 to 82"C during one Vt hour with 10$ relative humidity. The meat product was cooked with an internal temperature of 68°C , and then showered with cold water (8°C) for 10 minutes, followed by chilled water (1.6°C).The treatment conditions were sufficient to transfer smoke color, odor and flavor components from the casings to the frankfurters therein. Immediately after the treatment, colorimetric values were obtained using a Gardner XL-23 colorimeter with a 1 cm opening, standardized with a white plate, all in accordance with the standard procedure described in the instruction manual for the Gardner XL-23 tristimulus colorimeter, which is often used to measure color and light intensity in the industry. Three locations on each of the 10 frankfurters from each treatment were selected from the measurements. The reading locations were approximately 2.54 cm from each frankfurter end, and in the middle. Colorimetric "L"- and " A"- values were taken. The results of these tests for peelability and colorimetric values are presented in Tables K and L. Analysis of Table K suggests that the peelability of the 1 beef test based on the use of low-tar liquid smoke and treated cellulose casings according to the invention (sample K3) was excellent using resolution for increased readability. The peelability of the meat preparation with a high collagen content (sample K6) was good with the use of an internally applied solution for increased peelability• Analysis of Table L suggests that the frank furter product produced in samples treated with low-tar liquid smoke has a darker and more red color than frank - fur products produced in casings • that were not treated with a liquid smoke preparation.

Example X

Several non-fibrous cellulose casings for frankfurters were treated as 1 Example IV ("Royal Smoke AA" - derivatized solutions and methylene chloride extraction of tar), except that the improved peelability solution from Table F was then sprayed onto the inner surface of the casing during creasing in an amount of 0.54 mg/cm<2 >case surface to improve the peelability of the cases. The pH value of the aqueous liquid smoke (liquid smoke preparations Bj^ and Bg in Example I) used in these experiments was adjusted by the addition of 50% NaOH solution to obtain a pH value of 3.2 or larger, as shown in Table M. The casings treated with low-tar liquid smoke 1 Table M were stuffed with high-collagen meat emulsion of the composition in Table N.

The stuffed casings were then processed in the usual steps of boiling, showering with cold water and cooling, but without the usual fuming step. The casings were peeled off in finished frankfurters on a "high speed "Apollo Ranger" peeling maschine", and table 0 shows that these casings were peeled 100$ when the pH value was at least 4.1. This means that all frankfurters were separated from their casings at machine peeling speed without mechanical stopping of the peeling machines and without scratches in the frankfurter surface. Colorimetric values were also obtained by using the apparatus described in example 9. Table 0 also shows that each of the samples generally had better colorimetric values compared to the control samples CMC-8. All samples showed superior tenderness (the "L" values), but sample CMC-14 had lower redness ("a" value) due to a relatively high solution pH of 7.0.

Frankfurters that were treated in casings from example X exhibit an acceptable smoke flavor. •

Example XI

Staining ability was measured for different preparations that were aged at high temperature (relative to the controlled neutralization temperature during manufacture), for periods up to 25 days. In the first test series, "Royal Smoke AA" liquid smoke per se and the corresponding tar-poor liquid smoke, neutralized to a pH value of 6.0 at different temperatures in the range 5-30°C, were used, and aged at 37.8° C for up to 25 days. In another test series, "Charsol C-10" per se and the corresponding low-tar liquid smoke, neutralized at different temperatures in the same temperature range, were used, and also aged at 37.8°C for periods up to 25 days. In a third test series, "Charsol C-10" per se and the corresponding low-tar liquid smoke were also neutralized at different temperatures in the range of 35° C, and aged at 70° C for periods up to 22 days. In a fourth series of tests, "Royal Smoke AA" liquid smoke per se and the corresponding low-tar liquid smoke were neutralized at different temperatures in the range 5-30°C, and aged at 70°C for periods up to 25 days. The procedure (controlled temperature neutralization) for producing low-tar liquid smoke in these samples is the same as that described in Example II, and the results of these samples are reproduced in Table P.

Table P shows that the staining ability of tarry, liquid smoke per se is largely constant, that is, unaffected by high-temperature ageing. In contrast, the stainability of low-tar liquid smoke according to NO-PS will continuously decrease during high temperature aging at 21.1°C and 37.8°C for periods up to 25 days. This reduction is approximately constant and linear for the entire neutralization range of 5-30°C. Although these aging samples use samples produced by controlled temperature neutralization, other aging samples with tar-poor liquid smoke produced by (uncontrolled temperature) neutralization and solvent extraction will show the same phenomenon. These samples demonstrate

the chemical difference between tarry liquid smoke and tar-poor liquid smoke according to NO-PS

Example XII

A series of tests were carried out on aged casings according to the invention. These show that although the stain index for casings treated with tar-poor, liquid smoke decreases significantly from the Index on newly manufactured casings, surprisingly enough the stuffed food product used in aged casings has smoke color equivalents in colorimetric value corresponding to products made with fresh casings.

These aging samples include casings treated with tar-containing liquid smoke per se under largely identical conditions, and the stain index does not decrease for such casings to the same extent as the stain index decreased for casings treated with low-tar liquid smoke according to NO-PS This comparison shows the chemical difference between these two types of casings.

In these samples, "Royal Smoke AA" was applied to the outer surface of a 21 mm diameter cellulose sleeve, with a CMC-based coating on the inner surface to improve peelability. For the samples based on the casings of the invention, the liquid smoke per se was first brought into contact with methylene chloride in a volume ratio of 10:1 for liquid smoke solution: solvent. After mixing, the solution was left for 12 to 14 hours to form two layers. The separated, tar-poor, upper layer of liquid smoke was partially neutralized to a pH value of 5, and added to the outer surface of cellulose casings by the method according to example IV. Half of the casings were stuffed with a frankfurter emulsion of high collagen content, very similar to that of Table E, and processed in the conventional steps of boiling, showering with cold water and cooling, but without the usual smoke treatment. The other half of the casings were aged as in Table Q, and then used to make frankfurters in the same way. The results of these tests are reproduced in table Q. The colorimetric values were obtained with the same equipment as was used in example III, and by the same method as described there. It is understood that data from table Q cannot be quantitatively compared since the original stain index (fresh S.I.) is different and different aging conditions were used. The data qualitatively supports the general condition that stuffed food products produced by using aged casings have a smoke color that is unaffected by casing age, regardless of the fact that the stain index in casings decreases with age.

Example XIII

All the treatment experiments described above included non-fibrous casings of cellulose, but the invention is also useful for the treatment of fibrous casings of cellulose. In this experiment, fibrous casings with a flat width of 16 cm were treated with low-tar liquid smoke, produced by "Royal Smoke AA" per se liquid smoke solution, by the controlled temperature neutralization of Example II. The untreated casing was rolled up and passed through a bath of low-tar liquid smoke solution with only one dip, and immediately rolled up to form a new roll. This method meant that excess solution which had been applied to the casing's outer surface could absorb from the bladder and penetrate the casing wall while the casing was on the roll, so that the final, treated casing was obtained. The dipping operation was carried out so that the interior of the casing was not in contact with the tar-poor, liquid smoke. The residence time in the solution was only a fraction of a second, and the speed of movement of the casing from roll to roll was approx. 107 m/minute. The tensile stress in the casing was approx. 44 N. The estimated application of smoke solution to the casing was approx. 3.7 mg/cm<2> casing surface. Special methods for producing a fibrous casing which has been treated with liquid smoke are not part of the present invention, but are described in US-SN 301 276 (Chiu). The fibrous casings thus treated were then crimped in the usual manner, and separate casing samples were then stuffed with ham and bologna sausages, and processed under normal stuffing and processing methods, except that smoke was not added in a smoke chamber. The ham and bologna products had an acceptable colour, smell and taste, which was applied from the smoke-treated casings according to the invention.

Example XIV

This experiment shows the production of fibrous casings treated with low-tar liquid smoke where the liquid was produced from tar-containing liquid smoke by the solvent extraction method.

The low-tar liquid smoke was prepared by contacting "Royal Smoke AA" per se with methylene chloride as in Example I, but without pH adjustment. The rest of the methylene chloride was removed from the tar-poor fraction by using negative pressure on the container with the liquid. This low-tar liquid smoke was used to prepare a treated fibrous casing using the same fibrous casing and process as described in Example XIII. The treated fibrous casings were then crimped in a known manner, and separate casing samples were then stuffed with ham and bologna sausages, and processed under normal stuffing and processing methods, except that smoke was not added in a smoke chamber. The ham and bologna products had an acceptable colour, smell and taste.

In a preferred embodiment, a low-tar liquid smoke preparation is produced from a tar-containing liquid wood smoke solution with a total acid content of at least 7% by weight, and preferably a total acid content of at least 9% by weight. Total acid content is a qualitative measure of the tar content and staining ability (defined above) of liquid wood smoke per se used by the manufacturers. In general, a higher total acid content means a higher tar content. The same applies to the total content of solids in liquid smoke per se. The procedures used by liquid wood smoke producers to determine total acid content (total acidity) and total amount of solids are as follows: Determination of total acid content for tarry. liquid smoke. 1. Weigh accurately approx. 1 ml of liquid smoke (filtered if necessary) in a 250 ml beaker. 2. Dilute with 100 ml of distilled water and titrate with standard 0.1N NaOH to pH 8.15 (pH meter). 3. Calculate total acid content as weight-$ acetic acid with the following equation:

1 ml of 0.1000N NaOH = 6.0 mg of HAc

As will be explained below, this dilution-filtration method is also used to measure the total acid content in tar-poor, liquid smoke, which is not at least partially neutralized.

Determination of total amount of solids.

1. Pipette approx. 0.5 ml of liquid smoke on a tared 6 cm moistened aluminum dish fitted with a dried Whatman No. 40 fllterpaplr and weigh accurately. Liquid smoke should be ready,

and filtering are met to ensure this.

2. Dry for 2 hours at 105°C in a forced circulation oven or 16 hours at 105°C in a conventional oven.

3. Cool to room temperature in a desiccator and weigh.

4. Calculate the total amount of solids as weight-$ of liquid smoke.

Table A lists the most commonly used and commercially available tarry, aqueous, liquid wood smoke preparations together with the total acid content as reported by the manufacturers. Total content of solids, staining ability and % light transmission at 590 nm are also reproduced for the sake of comparison. It should be noted from Table A that wood smoke solutions per se with a total acid content of less than 10 wt-$ have a high light transmission of approx. 60$ and low stainability. Their tar content is so low that water compatibility is high. Consequently, there is no need to remove tar from such wood smoke solutions. Their staining ability is also so low that they are unable to provide the same smoke color and smoke flavor function as low-tar, liquid smoke preparations.

However, it should be noted that such liquid smoke preparations with a low tar content can be concentrated, for example, by evaporation, and that liquid smoke solution concentrated in this way can have the same properties as tarry liquid smoke, which can be successfully treated to produce a tar-poor, liquid smoke. This means that such concentrated, tarry, liquid smoke preparations have a higher total acid content, total solids content and staining ability.

In another preferred embodiment, the low-tar, liquid smoke preparation has a total acid content of at least approx. 7 weight-$ and preferably a total acid content of at least approx. 9 weight-$. The total acid content of low-tar liquid smoke is a function of the acid equivalent because the analytical procedure for determining the total acid content of low-tar liquid smoke provides a measure of the free acid plus the acid salt resulting from partial neutralization. Total acid content is a qualitative measure of staining ability (defined above), and not only tarry liquid smoke, but also tarry liquid smoke produced therefrom by the methods described. If the tar-poor preparations are not partially neutralized to a pH value not greater than 4 for the purposes of the invention, the total acid content is measured by the same dilution-titration method as described for measuring the total acid content of tar-containing (per se) liquid smoke. If the low-tar, liquid smoke preparation is at least partially neutralized to a pH value greater than approx. 4, the total acid content is measured by the steam distillation reflux-titration method. This method is theoretically capable of quantifying the acid and acid salts such as acetate and formate that are formed in the at least partially neutralized, tar-poor liquid smoke.

From a reaction point of view, the acid percentage in the aqueous liquid smoke (in free or salt form) remains constant during at least partial neutralization, that is, during controlled temperature neutralization. However, recovery of these acids is only 60$ due to the inability to obtain a complete azeotropic recovery at reasonable distillation volumes. At the present time, no other method is known for the quantitative recovery of all the acid components from tar-poor, liquid smoke, regardless of condition. In these circumstances, the results obtained with the steam distillation recovery titration are multiplied by a factor of 1.4 for conversion to the total basis for total acid content used for tarry liquid smoke. Measurement of total acid, phenol and carbonyl content in smoke-treated casing is determined by the following methods.

Determination of total acid content for at least partially neutralised, tar-poor. liquid smoke and treated casings made from it.

The determination is made from the m-equivalents of sodium hydroxide required to neutralize the m-equivalents of acetic acid which is distilled by acidifying at least partially neutralized, tar-poor, liquid smoke, or treated casings produced from preparations. "m-equivalent" is the weight in grams of a substance present in 1 ml of a solution. The procedure is as follows: 1. Weigh exactly 5 g of low-tar smoke into a tared 800 ml Kjeldahl flask. For holsters, measure exactly 650 cm<2 >of holster surface. 2. Add boiling pieces and 100 mL of 2$ H2S04 to the flask, where the reaction is

2NaAc + H2SO4 2HAc + Na2SO4.

3. Place a 500 mL Erlenmeyer flask containing 100 mL of deionized water on an ice bath and use this water to

capture the distillate.

4. Connect the Kjeldahl flask containing the sample to the steam distillation apparatus. 5. Distill the sample to the distillate volume in the collected

The Erlenmeyer flask reaches 500 ml.

6. Titrate 100 ml of distillate with 0.1N NaOH to an end point pH value of 7.0, where the reaction is

HAc + NaOH > NaAc + H2O.

7. Calculate the measured acid content as weight of acetic acid on the basis that 1 ml of 0.1N NaOH corresponds to 6.0 mg of HAc, so that measured

acid content in mg - ml titrate x 6.0.

8. Total acid content = 1.4 x measured acid content in ml.

9. For liquid smoke, express the total acid content as weight—$ of the original liquid smoke sample. For casings, express the total acid content as mg acid per 100 cm<2 >case surface.

The total acid content of several tar-poor preparations has been measured by the steam distillation recovery-titration method, and is reproduced in table R. For comparison, the same method is used to measure the total acid content in tar-containing, liquid smoke per se, from which the preparations were prepared , and these results are also reproduced in table R. It is noted that the values are quite similar for the same type of liquid smoke, whether it is tarry or tarry. Thus "Royal Smoke AA" per se has a total acid content of 11.1$, and tar-poor, "Royal Smoke AA" has a total acid content of 12.2$. For further comparison, "Royal Smoke AA" per se measured by the dilution-titration method used by the manufacturers has also been included in Table R. This value of 11.4$ is also very similar to the values for "Royal Smoke AA" based on the steam distillation recovery titration method. Determination of phenol and carbonyl content in casings treated with liquid smoke.

The samples are prepared by measuring and steam distilling 0.13 to 0.19 m<2> outer surface of casings as described in the procedure for determining total acid content. The reagents for the phenol determination are prepared using distilled water in the following way: 1. Color solution: Dissolve 100 mg of N-2,6-trichloro-benzoquinone-imine in 25 ml of ethanol, and cool. For the sample, dilute 2 ml

to 30 ml of water.

2. Buffer, pH-8.3: Dissolve 6.1845 g of boric acid in 250 ml of water. Dissolve 7.45 g of potassium chloride in 250 ml of water. Dissolve 0.64 g

NaOH In 80 ml of water. Mix the three solutions together.

3. 1$ NaOH: Dissolve 1.0 g of NaOH in water. Dilute to 100 ml.

4. Standard solution: Dissolve 0.200 g of dimethoxyphenol (DMP) in 2000 ml of water. Then dilute portions of this solution so that you get standard solutions containing 1, 2, 4, 6 and 8 ppm DMP.

The procedure for phenol determination is a modified Gibbs method as described in Wild F., "Estimation of Organic Compounds", 143, 90-94, University Press, Cambridge, 1953. In this procedure the sequence is as follows: 1. In a 25 ml flask mix 4 components in the following order: 5 ml buffer pH 8.3, 5 ml casing distillate standard or water (blank), 1 ml 1$ NaOH, 1 ml

diluted color reagent.

2. Shake, put on card and place 1 dark for 25 minutes.

3. Read the absorbance at 580 nm.

4. Prepare a standard curve using the absorbance as the abscissa and the standard concentration as the ordinate. Extrapolate concentration DMP in the casing distillates from

this curve.

5. Calculate mg DMP/100 cm<2> casing using the following equation:

The reagents for carbonyl determination are the following:

1. Saturated solution of recrystallized, 2,4-dInitrophenylhydrazine (DNP) in carbonyl-free methanol.

2. Concentrated HC1.

3. 10$ alcoholic KOH: Dissolve 10 g KOH 1 20 ml distilled water and dilute to 100 with carbonyl-free methanol. 4. Standard solution: Dilute 1 ml of 2-butanone (methyl ethyl ketone) (MEK) to 2000 ml with distilled water. Then dilute portions of this solution to obtain standard solutions containing 0.8, 1.6, 2.4, 4.0 and 8.0 ppm MEK.

The procedure for carbonyl determination is a modified Lappan-Clark method as described in the article "Colorimetric Method for Determination of Traces of Carbonyl Compounds", Anal. Chem., 23, 541-542 (1951). In this procedure the sequence is as follows: 1. In a 25 ml flask, mix the three components in the following order: 5 ml 2,4-DNP solution, 5 ml caslng distillate, standard or water (blank), note: casing- the distillate may require further dilution, 1 drop

concentrated HC1.

2. Leave the mixture for 30 minutes in a 55"C water bath.

3. After rapidly cooling the mixture to room temperature, add 5 ml of 10% alcoholic KOH, shake and set aside for 30

minutes.

4. Read the absorbance at 480 nm.

5. Prepare a standard curve using the absorbance as the abscissa and the standard concentration as the ordinate. Extrapolate the concentration of MEK in the casing distillates from this curve. 6. Calculate mg MEK/100 cm<2> caslng using

Absorbent ability.

It should be remembered that both stain ability and stain index measurements include chemical reactions and apparently for this reason the values measured at room temperature will decrease during aging at high temperature. As shown in Example XII, this reduction is not an accurate indication of the smoke color that occurs in stuffed food products when casings that have been aged after treatment with low-tar liquid smoke are used.

Under these circumstances, further measurements which do not include chemical reaction are used to determine the color ability of liquid smoke and casings treated with it. This measurement for liquid smoke is called "absorbing ability", and the measurement method for casings treated with liquid smoke is called "absorbing index".

In the method for measuring absorptive capacity, 10 mg of liquid smoke (which is either tar-containing or tar-poor) is placed in a disposable tube and 5 ml of methanol is added. The two components are mixed by inverting the tube and the ultraviolet absorption value of the mixture is measured at 340 nm. This particular wavelength is chosen because spectroscopy measurements with many liquid smoke preparations indicate the greatest linearity in this wavelength range. Absorbency measurements for different types of liquid smoke per se are given in Table A. A curve of these absorbency measurements as a function of total acid content or total solids content gives a largely linear relationship. It should be noted that while the tar content is a significant contributor to the measurement of absorbency, it has been found that tar contributes little, if at all, to the coloring of the food. In commercially available smoke preparations, the absorptive capacity includes a measurement of the tar content and color components such as carbonyl, phenols and acids. This means that the absorptive capacity in smoke per se and in tar-poor smoke can be used to rank them according to smoke-colouring capacity. However, absorbent capacity in liquid smoke per se cannot be numerically compared with absorbent capacity in tar-poor smoke used according to the invention, due to the absorbent effect of the tar. Furthermore, the absorptive capacity of tar-poor smoke produced by one method cannot be numerically compared with the absorptive capacity of tar-poor smoke produced by another method, because the degree of tar removal by the two methods may be different. For example, low-tar liquid smoke produced by the solvent extraction method has a lower tar content than low-tar liquid smoke produced by controlled neutralization, based on the same starting material. Unlike colour, the absorptive capacity of liquid smoke does not decrease with ageing.

Example XV

A series of absorptive capacity measurements were carried out on various tar-poor liquid smoke preparations. A group of per se liquid smoke was treated with controlled temperature neutralization using NaOH flakes and with a neutralization temperature of 10-15"C. Another group of per se samples was first neutralized in the same way to remove a first tar part , and then brought into contact with methylene chloride in a ratio of 10:1 between liquid smoke and solvent to remove another tar part according to the procedure of Example I. These measurements are reproduced in Table S.

Table S should be interpreted in the light of the preceding discussion concerning the effect of the tar content on the absorptive capacity of liquid smoke.

Table S shows that the absorbent capacity in tar-poor, liquid smoke is generally somewhat lower than the absorbent capacity in the tar-containing smoke from which it is produced. This principle does not apply to "Charsol C-6" and "Charsol C-3" as these preparations have a very low tar content from the start.

Table S also shows that the absorptive capacity 1 tarry smoke used for the production of tar-poor, liquid smoke according to NO-PS 823407 should be at least 0.25 if no more treatment steps are to be used. Table S also shows that "Charsol C-3" per se does not satisfy this requirement.

The absorbent capacity of this tar-poor smoke must be at least approx. 0.15 to obtain an acceptable smoke color on the food produced in casings according to the invention. It appears that the controlled temperature neutralization produces a low-tar, liquid smoke that just satisfies the lower limit. In a preferred embodiment, the absorptive capacity in tar-poor liquid smoke is at least 0.25.

In another preferred embodiment of the tar-poor, liquid smoke, the absorbent capacity is at least approx. 0.25 at 340 nm wavelength, and the light transmission is at least 65$. This level of absorbency is easily achieved as discussed above. The procedure for measuring light transmission and achieving at least 65% light transmission is discussed below.

Absorption. loan index.

In the procedure for measuring the absorption index, a 12.9 cm<2> smoke-treated casing is cut out after drying and placed in 10 ml of methanol. After 1 hour, the methanol has extracted all the red components from the casing and the ultraviolet absorption value of the resulting methanol containing smoke components is determined at 340 nm. As with the measurement of absorptive capacity, a wavelength of 340 nm was chosen as spectroscopic measurements with many extracts of liquid smoke from treated casings indicate the greatest correlation with smoke load in this range.

Example XVI

A series of absorption index measurements were made on the casings using four different types of low-tar liquid smoke produced by solvent extraction and produced by controlled temperature neutralization. In each case, the neutralization was to a pH value of 5.0. The resulting low-tar smoke solutions were applied at various loads to an outer surface of frankfurter size non-fibrous cellulose gel casings as in Example IV. The results are reproduced in Figure 8, where the area of liquid smoke from "Royal Smoke AA" is shown as diagonal lines, liquid smoke from "Charsol C-12" is shown as horizontal lines, and liquid smoke from "Royal Smoke B" are shown as vertical lines. In addition, one finds a simple line based on measurement with a concentrated form of low-tar, liquid smoke, produced from "Royal Smoke AA" liquid smoke per se at controlled temperature neutral in sering.

To use this figure, first select the desired degree of smoke color with regard to absorption index, and the type of tarry, liquid smoke to be used for tar removal by, for example, one of the three methods described. Next, the required load of a special, tar-poor, liquid smoke on the casing is determined to achieve these properties. In figure 8, 1 mg/in<2> corresponds to 0.155 mg/cm2. The correlation between smoke color and absorption index is shown in the following example XVII.

Example XVII

A series of colorimetric tests were carried out using frankfurters prepared in the manner described above from preparations in Table N in non-fibrous cellulose casings treated with various liquid smoke preparations prepared as described above. The results of these tests are reproduced in table T.

In an attempt to quantify the desired changes in light intensity to ensure adequate color development, the L value was determined and is given in Table T. In this case, the meat emulsion was 50$ beef cuts and 50$ regular pork trimmings, and the L values were considered as too low if a 1.4-unit change or less in light intensity occurred between L values measured on unsmoked control pods, compared to pods treated with liquid smoke.

Table T shows that if the absorption index is less than approx. 0.2, the smoke load is 0.62 mg/cm<2> or less. This level of smoke load usually does not produce a desired reduction in the light intensity of the meat product, i.e. the color development is usually considered insufficient. The average reduction in light intensity obtained with a liquid smoke load of 1.32 mg/cm<2> is quite satisfactory for most purposes, so that the corresponding index of at least 0.4 represents a preferred embodiment of the invention.

Table T also shows that the embodiment according to the invention largely gives the same coloring ability as the original tar-containing smoke. A comparison between samples no. 2 and 3 and sample no. 10 shows that the tar content in liquid smoke can have very little influence on the color ability of the liquid smoke. For practical purposes, the light intensity of frankfurters of 2.9 to 3.2 for case samples No. 2 and 3, respectively, is roughly equal to the light intensity of 3.4 for sample No. 10.

It should be noted that many factors associated with the meat emulsion and processing conditions can affect the background color and thus the L and $L values. For example, meat gets much of its color from myoglobin. The color associated with the myoglobin content in meat has been shown to be dependent on the chemical reaction between myoglobin and the treatment, which in turn is affected by treatment conditions such as temperature, humidity, time and air velocity. Consequently, the L value in Table T is only relevant for these particular samples.

Other tests have shown that the ability to retain the color when aging at room temperature (21°C) is approximately the same for casings treated with low-tar liquid smoke according to the invention as for casings treated with tar-containing smoke. As an illustration, the arithmetic mean of L over a 3-month period for casings treated with low-tar liquid smoke from "Royal Smoke AA", prepared by the neutralization method to a pH value of 5.5, was substantially the same for the two types of liquid smoke with a $ L reduction of approx. 1.6.

All the aforementioned tests concerning the absorption index were carried out either on non-fibrous cellulose casings of the same diameter immediately after treatment with liquid smoke and drying, or on frankfurters treated in the casings. Other samples have shown that the absorption index is not significantly affected by variations in the casing thickness. Other tests have again shown that absorption index values for fibrous casings treated with tar-poor, liquid smoke are approximately the same as the absorption index values obtained for non-fibrous, cellulose casings with the same smoke load. As an illustration, an absorption index of approx. 0.4 with a fiber-reinforced cellulose casing of 115 mm diameter, treated with low-tar liquid smoke from "Royal Smoke AA", with a loading of 1.57 mg/cm<2> outer casing surface. The absorption index for a non-fibrous cellulose sheath, treated in the same way, is found for other samples to be approx. 0.4.

Example XVIII

A series of tests was performed on frankfurter-sized, tar-free, non-fibrous cellulose casings to demonstrate the minor effect of high temperature aging on absorbent index. Low-tar smoke used to treat these casings was produced in some cases by controlled temperature neutralization. In other cases, a first portion of the core was removed by this method and the resulting partially tar-poor smoke was then contacted with a suitable solvent in accordance with the solvent extraction method for further tar removal. The advantage of this sequence is that the amount of solvent required for the extraction can be reduced.

To produce low-tar smoke using only controlled temperature neutralization, "Royal Smoke AA" per se was neutralized to pH 5.0 by addition of NaOH flakes with a neutralization temperature maintained at 10-15°C. In some cases, tar-poor liquor for this process was then contacted with methylene chloride, with a liquid smoke:solvent ratio of 10:1. Absorption index measurements were obtained from casings treated with low-tar smoke immediately after treatment and drying, and after storage periods of 5 and 12 weeks at room temperature. Other samples of the same sleeve were heated to 37.8°C, and absorption index measurements were taken at the same time intervals. These measurements are reproduced in table U.

Table U shows that aging has no significant effect on the absorption index. The requirements for the absorption index are based on measurements at room temperature.

L. vsoverfgrlng

It has previously been said that the tar-poor preparations described must have a light transmission of mint 50$. Percent light transmission (in relation to water) is inversely related to the tar content in the liquid smoke, i.e. a high tar content results in a cloudy liquid with low light transmission. The procedure for measuring the light transmission is to accurately mix 1 ml of the liquid smoke sample with 10 ml of water, and determine the turbidity transmission at 590 nm wavelength on a spectrophotometer. The higher the percentage transmission reading, the lower the residual tar concentration in the liquid smoke.

The desired light transmission of at least 50$ and preferably 65$ can be achieved by any of the methods described above for preparing the tar-poor preparations, either alone or in combination, that is, the neutralization method, the controlled temperature neutralization method and the solvent extraction method. Furthermore, all tar-poor preparations as prepared in Examples I and II and used in Examples III to XVIII had a light transmission of at least 50$.

When using the neutralization method or controlled temperature neutralization, one should mix a sufficient amount of pH-regulating component with liquid smoke per se (typical analysis transfer of less than about $10), to raise the pH value above about 4 and preferably to at least 6, after which percent light transmission increases to a high level. As shown in Figure 5 of the above-mentioned, related application "Controlled Temperature Neutralizatlon Method", this is increased very quickly, and the slope of the 1-$ light transmission versus liquid smoke pH curve is approximately vertical. Above a pH value of approx. 8, tar tends to redissolve, so there is no advantage in raising the pH above this level. Light transmission values for tar-poor smoke produced from several tar-containing liquid smoke preparations per se were measured at pH approx. 6, and is reproduced in Table V. These preparations are prepared by controlled temperature neutralization using controlled addition of 50% NaOH liquid, while the mixture was kept at a temperature of approx. 15'C during mixing using a submerged, portable spiral type cooling unit.

If one chooses the solvent extraction method to produce low-tar smoke, the desired percent light transmission can be achieved by selecting the solvent, and also controlling the volume ratio between liquid solution and solvent. Generally, the highest levels of light transmission are obtained with the largest amount of solvent in relation to liquid smoke, but the cost of liquid extraction will increase with increasing solvent use. Representative light transmission values for various suitable solvents at specified ratios of "Royal Smoke AA" to solvent are given in Table W.

Example XIX

It has previously been stated that tar-poor preparations preferably have a light transmission of at least 50$ in the entire visible area, which is an indicator that a significant part of the tar content has been removed so that tar formation is avoided during the casing treatment with the preparation. This was demonstrated with a series of samples where "Royal Smoke AA" under extraction conditions was brought into contact with methylene chloride in different volume ratios of liquid smoke:solvent. A tar-poor, liquid smoke fraction was separated, and the light transmission measured as described above. Weight-$ non-volatile materials (including tar) in this tar-poor fraction were also determined. Data for these samples

are reproduced in table X and figure 9.

Data from figure 9 shows that the light transmission is strongly affected by the volatile material (including tar) in the range from 0 to 50$ light transmission. This means that one must gradually reduce the tar content of the liquid smoke by, for example, solvent extraction or controlled temperature neutralization, in order to gradually increase the light transmission of the liquid smoke from 0 to approx. 50$. When sufficient tar is! removed to obtain a light transmission of approx. 50$ gives you a plateau and a further improvement in light transmission does not primarily depend on further removal of tar.

Although preferred embodiments of the invention have been described in detail, modifications may be made, and some features may be used without others. For example, tarry liquid smoke per se which has been successfully treated to remove tar as described can be further concentrated in a manner known per se before or after treatment, to produce the tar-poor liquid smoke preparations. This may be desirable if you wish to apply a highly concentrated form of low-tar smoke to the casing wall.

The treatment with low-tar, liquid smoke for a tubular food casing according to the invention is preferably carried out under controlled environmental conditions where the presence of small metal particles is reduced to a minimum. This is an important requirement since metal wear particles (primarily iron, copper, brass) in contact with the casings react with the coating of liquid smoke, leading to autoxidation, discoloration and degradation of the cellulose in the treated casings. Discolouration and degradation of cellulose only takes place in the immediate area around the metal contamination, and rarely extends beyond a diameter of 2-10 mm. The cellulose degradation can occasionally be severe enough to cause casing rupture during tamping. The construction materials in the treatment apparatus are an important factor in minimizing small metal particles. These materials should (1) have high abrasion resistance and (2) be non-reactive to liquid smoke. It has been determined that certain metals and alloys are compatible with these strict requirements. These are: certain aluminum alloys, chrome plating, tin alloys and certain stainless steels. Care must also be taken in the second stage of casing manufacturing and processing to reduce the presence of metal particles.

Example XX

Four samples of low-tar liquid smoke were prepared with varying light transmission using controlled temperature neutralization. Liquid smoke solution per se that was used was "Charsol C-12" with an absorbance of 0.2 at 340 nm wavelength and pH value approx. 2. Each of the four samples was prepared substantially as in Example II except that each was neutralized to a different pH so that a different light transmission value was obtained for each of the resulting tar-poor liquid smoke solutions.

The samples were neutralized by adding NaOH flakes and the temperature was kept between 10 and 25° C during the neutralization by using cooling coils. NaOH was used so as to neutralize the samples to light transmission values of 20, 50, 60 and 80$. This was achieved by adding an amount of NaOH which gave the final pH value indicated in Table Y. After the desired amount of NaOH had been added, the tar precipitate was separated from the supernatant liquid by filtration so that a tar-poor, liquid smoke was obtained. The light transmission was measured by diluting 1 ml tar-poor, . liquid smoke, with 10 ml of water, and to measure the transmission in relation to water on a spectrophotometer with wavelengths of approx. 715 nm. A control test was also carried out in the same way, except that smoke per se was neutralized to pH 6.0. In table Y, the pH value and light transmission are shown for tar-poor, liquid smoke.

The samples were applied to non-fibrous frankfurter hysters of gel (size no. 25) so that 15.5 g were obtained per m<2> liquid low-tar smoke, with the apparatus and method described in Example V. The casings were dried as in Example V for 3 minutes at a drying temperature of between 80 and 120°C.

During the application of liquid smoke, the casing was observed for tar stains, and the guide and pinch rollers in the drying unit were observed for tar build-up. Results of the observation are reproduced in table Z.

As can be seen from the above results, problems due to the presence of tar in the tar-poor smoke solution as seen with lower transmission values, become less when the tar content is lowered or the light transmission values are increased. With low-tar, liquid smoke with a light transmission of approx. 20$, the difficulties caused by the tar, and especially the sticking to the pinch rollers, render the coating process impossible in operation, and the preparation therefore unacceptable. When the light transmission rises to approx. 50$, there are still difficulties such as weak adhesion on the rollers and commercially undesirable tar spots on the casing, but the application of liquid smoke can still be carried out and useful casings can still be produced. With a light transmission value of approx. For $60, a casing can be produced that has few tar stains and is commercially more desirable even if stains form on the casing after a longer period of operation. At higher light transmission values, in sample 4 and the control, a casing is obtained which is commercially acceptable and where there are no tar spots on it, and the coating process can be carried out on a continuous basis without tar build-up, or adhesion difficulties which would lead to the process having to is stopped.

Example XXI

Four samples of tar-poor smoke were prepared with varying light transmission using the solvent extraction method. Smoke solutions that were used were "Charsol C-12" with an absorption capacity of 0.5 with a wavelength of 340 nm, and a pH value of approx. 2. Each of the three samples was prepared largely as in Example I except that each sample was solvent-extracted so that a different light transmission value was obtained for each of the resulting tar-poor liquids. To a quantity of methylene chloride was added approx. 3785 ml of liquid smoke per se, and the liquid was mixed by stirring or shaking. The methylene chloride containing tar was separated from the liquid smoke by decantation. The light transmission was varied by varying the amount of methylene chloride used in the extraction. The light transmission was measured by diluting 1 ml of low-tar liquid smoke with 10 ml of water, and measuring the transmission 1 ratio to water on a Hitachi model 100-60 spectrophotometer at a wavelength of 590 nm. Table AA shows the amount for each sample of methylene chloride (MeClg) to extract tar from the smoke, and the pH value and light transmission in the tar-poor product.

The above-mentioned samples were applied to a non-fibrous frankfurter sleeve made of gel (size no. 25) with the apparatus and method from example IV, so that a load of 15.5 g of liquid smoke was obtained per m<2> casing surface. The casings were dried as in example IV for 3 minutes with a drying temperature between 80 and 120°C.

During application of the low-tar smoke, the casings were observed for tar spots, and the guide rolls and pinch rolls in the drying unit were observed for tar build-up.

The results of the observations are reproduced in table BB.

As can be seen from the above results, the problems due to the presence of tar in the tar-poor liquid smoke preparation reflected at lower light transmission values were reduced when the tar content was lowered or the light transmission was increased. With low-tar, liquid smoke with a light transmission of approx. 40$ the difficulties caused by the tar and especially the sticking on the pinch rollers, make the coating process impossible to carry out, and this preparation is therefore unacceptable. With a light transmission of approx. 50$, there are still difficulties in that, for example, tar stains form on the casing after a certain time. Blemish-free casings are produced, however, during the original operating time which is acceptable from a commercial point of view. When the light transmission increases to 60$, the operating time before spots appear is longer, and therefore the coating process becomes more practical. With a light transmission of approx. 84$, you can get an extended operating time without problems with staining and tar build-up. Tar-poor, liquid smoke with high light transmission can be used in a coating process without problems involving the build-up of tar or other difficulties that lead to the coating process having to be interrupted.

Claims (3)

1. Method for producing a smoke-coloured food product where a tubular food casing is provided with a coating of tar-poor liquid smoke which is produced from a tar-containing liquid smoke, characterized in that the liquid smoke is applied to a casing surface 1 in a sufficient amount to give an absorbent index of at least approx. 0.2, preferably 0.3, at 340 nm wavelength, where said tar-poor, liquid smoke coating gives a casing extract with an absorbance at 210 nm wavelength that is not more than approx. 60$ of the absorbance of a corresponding extract from an identical casing, with a comparable coating of said tar-rich liquid smoke sufficient to provide substantially the same absorbent index as said tubular food casings treated with low-tar liquid smoke; stuffing casings treated with liquid smoke with foodstuffs, and treating the foodstuff in casings treated with liquid smoke under conditions sufficient to convert said foodstuff into an edible food product and form smoke color on the surface of the resulting food product. 2. Method according to claim 1, characterized in that a tubular food casing is provided from a gel made from cellulose without fiber reinforcement with a coating of low-tar liquid smoke, made from tar-containing liquid smoke with a total acid content of at least 10% by weight, which is applied to the surface of the casing in sufficient quantity to provide an absorptive index of at least 0.2, preferably at least 0.3, at 340 nm wavelength, wherein said tar-poor liquid smoke coating provides a haze value not greater than the haze value of an identical casing without said coating of liquid smoke smoke; by stuffing casings treated with liquid smoke with foodstuffs, and by treating the food in casings treated with liquid smoke under conditions species that are sufficient to produce an edible food product and form a smoke color on the surface of the food product. 3. Method according to claim 2, characterized in that said fog value is less than the fog value for said identical casing without said liquid smoke coating.