DE68911534T2 - Liquid smoking product made by rapid pyrolysis. - Google Patents

Description

The invention relates generally to the use of liquid smoke produced by a rapid pyrolysis process for processing, seasoning and coloring meat, fish, poultry and other food products.

Background of the invention

The use of liquid smoke solutions instead of smoking by direct contact with smoke generated from wood is a common industry practice. When liquid smoke is applied to the surface of meat and other protein-containing foods, it not only imparts a distinctive smoke flavor to the piece, but it reacts with the proteins, creating the dark coloring typical of smoked foods.

One of these processes for producing liquid smoke used commercially for surface applications is described in US Patent 3,106,473. This product is produced by partially burning hardwoods, i.e. sawdust, using a deficit of air and then dissolving the desired smoke components in water. A heavy, water-insoluble phase is separated which contains tar, polymers, polycyclic aromatic hydrocarbons, including benz[a]pyrene, waxes and other undesirable products that are unsuitable for use in food applications.

Smoke is a complex and variable mixture of chemicals resulting from pyrolysis reactions and contains gaseous compounds that are normally liquid at room temperature. Pyrolysis is the general term for thermal decomposition of any organic matter (i.e. wood, plants, fossil fuels, etc.) and can occur during a combustion process or without combustion. In the first case, the oxidation or combustion of a portion of the organic matter for the heat required for evaporation and decomposition of the residue. If combustion does not take place, the heat must be supplied indirectly from another source (ie by radiation, a solid or gaseous heat transfer medium, or by conduction across the reactor walls, etc.).

Pyrolysis produces liquids (i.e., condensable vapors), gases (non-condensable), and solids (char and ash) in varying proportions depending on the reaction conditions. The liquids can be further divided into water-soluble organics and water-insoluble tars. It is known that the desired active ingredients for smoke flavoring are found among the water-soluble, condensable vapors (liquids).

Currently, liquid smoke is produced by performing conventional pyrolysis, which is characterized by relatively slow thermal reactions occurring at moderate temperatures. In the commercial processes, the wood feedstock is dried, ground into sawdust and fed into a reactor system. A typical, average reactor temperature is approximately 420ºC. Depending on the heating method, the temperature gradient in the reactor can range from 600ºC in the heater to 250ºC at the surface of the bulk of the wood. Residence times of solids (wood/char) and vapors are approximately 10 minutes and 1 minute, respectively.

Conventional pyrolysis produces liquid, gas and char yields that are typically 35, 35 and 30 wt% of the wood feedstock, respectively. Since the water-insoluble components are between 50 and 65 wt% of the total liquid obtained from the wood content, the net yield of unpurified liquid smoke is relatively low (i.e. 12-20 wt% of the wood feedstock).

The pyrolysis products are often passed through a water bath or a gas scrubber. The gaseous products flow through the water bath. The solids and water-insoluble tars precipitate in the water, while the water-soluble organic substances are concentrated in the water as liquid smoke.

Although there are several hundred different chemical species present in liquid smoke, liquid smoke products are characterized by three classes of chemicals that relate to different functional groups. The three classes are 1) acids, 2) carbonyls, and 3) phenols.

This classification by functional groups is useful because phenols are the main flavoring compounds, whereas carbonyls are mainly responsible for coloring and acids serve as preservatives. Acids and carbonyls make a minor contribution to flavoring and they improve the surface characteristics of the meat product.

Acids are measured by titratable acidity and calculated as acetic acid. Phenols are calculated as 2,6-dimethoxyphenol. The method for determining phenols is a modified Gibbs method described in the Journal of the Association of Analytic Chemists, XXV, 779 (1942). Carbonyls are calculated as 2-butanone. The method for determining carbonyls is a modified Lappan-Clark method described in Analytical Chemistry, 123, 541-542 (1959).

Another measurement method used to characterize liquid smoke is the degree of browning. The degree of browning is used in the smoking industry to measure the browning process of a liquid smoke seasoning. The degree of browning uses a spectrophotometric technique that uses optical density to measure the conversion of a reaction of carbonyls with a glycine solution. The degree of browning is determined by the difference between the absorption of the reacted glycine solution at 400 nm and a blank sample.

The application of liquid smoke solutions to meat and other food products can be done in several ways. If the characteristic smoke color is desired, individual pieces can be sprayed or dipped in a batch process or in continuous mode. If large batches need to be treated, an atomized cloud of liquid smoke can be used. Alternatively, sausages and

Hams are treated in vessels into which liquid smoke solutions have been introduced. In any case, if surface color is the main effect to be achieved, a measurement of the total amount of carbonyls is made to determine the amount of smoke required. These compounds react with the available amino groups of the proteins on the surface to form the smoke coloration. The concentration of a particular carbonyl, hydroxyacetaldehyde, is also a good indicator of the ability of the liquid smoke to produce coloration.

Older processes for producing liquid smoke suffer from relatively low yields of the desired product and relatively high yields of undesirable byproducts. In addition, the levels of benz[a]pyrene, a known carcinogen, are relatively high, requiring subsequent dilution of the captured condensable vapors with water to remove these compounds.

The need to dilute the captured condensables to limit the benzo[a]pyrene content to below 0.5 ppb prevents the production of liquid smoke with a total acidity of more than 13% or a browning ratio of more than 13.0 without subsequent concentration.

Recently, new processes have been developed for the rapid thermal processing of carbonaceous feedstocks. These processes have been called rapid or flash pyrolysis.

Fast or flash pyrolysis of wood or cellulose is a process that applies a high heating rate to the wood feedstock over a short period of time and then rapidly quenches the pyrolysis products to a temperature below 350ºC. The heating rate for fast pyrolysis is greater than 1000ºC per second and the steam residence time is less than 2.0 seconds.

WO-A-88/00935 discloses a process for producing an aqueous smoke solution for use in foodstuffs, which involves the pyrolysis of lignocellulosic biomass using a reactor suitable for rapid heat exchange and short gas residence times under the following conditions:

- The gas and steam residence time is less than 10 seconds

- the residence time of solids is equal to or greater than the gas and vapour residence time, and

- pyrolysis is carried out at 400-650ºC.

US-A-4 359 481 considers a process for producing a concentrate of liquid smoke for use in food by a degradative distillation of cellulose and/or lignin at 350-450°C, the smoke concentrate containing less than 0.2 ng of benz[a]pyrene and 0.90-1.60 g/l of phenolic compounds whose content to the total content of acids is 1:(17.0-47.0):(13.0-40.0).

While fast pyrolysis processes are known, research and development in this field have focused on the production of liquid and gaseous fuels and on optimizing the production of fuels with high energy values.

An object of this invention is to produce liquid smoke by using the water-soluble products of rapid pyrolysis, which instead of conventional liquid smoke leads to higher yields and concentrations of the desired products and to lower yields of gaseous and solid by-products, resulting in higher efficiency and consequent cost savings.

Specifically, fast or flash pyrolysis leads to higher yields of hydroxyacetaldehyde and higher yields of other carbonyls and lower yields of carbon, benz[a]pyrene and gas. The higher yields of carbonyls result in a higher degree of browning.

Further cost savings result from a faster reaction rate in fast or flash pyrolysis, which allows a higher efficiency of the process so that smaller reaction volumes are required to process a given amount of feedstock.

Another object of the invention is to provide a method for producing smoke-colored and smoke-flavored food products. by treating the food products with the aforementioned liquid smoke solution.

Other objects and advantages of the invention will become apparent from the following description and claims.

Summary of the invention

The invention includes a process that produces liquid pyrolysis products from fast or flash pyrolysis and uses the liquid pyrolysis products in a liquid smoke solution. The liquid smoke solution of the invention is achieved in high yields, i.e. with low char and tar formation. It contains less than 1.0 ppb and preferably less than 0.5 ppb of benz[a]pyrene, a known carcinogen, and has a higher coloring ability than liquid smoke produced by conventional processes.

The liquid smoke solution will impart the desired smoke color to the meat with a milder, less smoked flavor than expected from liquid smoke solutions from slow pyrolysis. The high ratio of carbonyls (the reactive compounds that cause the coloring) to phenols (the flavoring compounds) characterizes this property of relatively high coloring ability and low flavoring power of the liquid smoke solutions from fast pyrolysis.

The present invention provides a process for the preparation of an aqueous smoke solution for use in foodstuffs, in which wood pulp or cellulose is heated in the absence of oxygen to a temperature between 400 and 650°C within 1.0 s; in which the wood or cellulose together with the pyrolysis products obtained from the wood or cellulose are maintained at a temperature of between 400 and 650ºC for a period of between 0.03 and 2.0 seconds; in which the temperature of the pyrolysis products is reduced to below 350ºC within 0.6 seconds to obtain a liquid extract; and in which the liquid extract is isolated.

In a preferred process for preparing an aqueous smoke solution for use in food, wood pulp or cellulose is heated in the absence of oxygen to a temperature between 400 and 650°C within 1.0 second; maintaining a temperature between 400 and 650°C; maintaining the wood or cellulose together with pyrolysis products made from the wood or cellulose at a temperature between 400 and 650°C for a period between 0.03 and 0.60 seconds; reducing the temperature of the pyrolysis products to below 350°C within 0.6 seconds to obtain a liquid extract; the liquid extract is separated and collected, the liquid extract is diluted with water to cause partial phase separation and to obtain an aqueous solution having a benz[a]pyrene concentration of less than 1.0 ppb, preferably less than 0.5 ppb, and a degree of browning based on the phenol concentration of more than 8.9 to 1 and a ratio of the hydroxyacetaldehyde concentration to the acetol concentration of more than 5.5 to 1.

Another embodiment of the invention provides a method for seasoning and coloring foods by contacting the foods with an aqueous smoke solution produced by rapid or flash pyrolysis.

Another embodiment of the present invention provides a process for producing a liquid smoke solution by collecting a liquid condensed product obtained by rapid or flash pyrolysis of wood pulp or cellulose in an oxygen-deficient atmosphere without the addition of water; by mixing a portion of the liquid condensate from the pyrolysis with 0.25-25 parts by weight of water, and then separating the non-aqueous phase from the aqueous phase forming the desired liquid smoke solution.

Another embodiment of the invention provides a process in which sufficient water is added to produce a liquid smoke solution, wherein the ratio of the degree of browning to the phenol concentration is greater than 8.9 to 1.

Since the liquids in rapid or flash pyrolysis are produced without the addition of water, unlike others produced conventionally, they consist of a single phase. Due to the extremely high heating rate and short residence time, these solutions inherently have a low benzo[a]pyrene content. However, the levels, although at least an order of magnitude lower than those produced by conventional liquid smoke, are still too high for consumption in many countries. In order to reduce the benzo[a]pyrene to less than 0.5 ppb, an addition of water is therefore necessary to cause phase separation. Consequently, the invention has the appropriate water-soluble fraction of the rapid pyrolysis product for food.

The use of this inventive liquid in the liquid smoke flavoring technique results in a significantly improved liquid smoke that avoids a number of shortcomings of the conventional technique while at the same time providing improved yields and a better quality product.

Using the fast or flash pyrolysis processes, liquid product yields of up to about 80 wt.% can be achieved. With the correct operating parameters, char yields are about 6%, while the remainder of the reaction products are gaseous by-products. Char yields can be reduced to below 1% if desired.

Liquid smoke produced by rapid pyrolysis processes exhibit increased total levels of carbonyls, phenols and acids and have a greatly improved browning level. The total amount of water soluble carbonyls, phenols, acids, browning level of a representative sample of conventional liquid smoke and products according to the invention from two rapid pyrolysis processes are shown in Table 1 below. Table 1: Analysis of water soluble liquids Yield from wood Sample source Total carbonyls (% w/w) Total phenols (% w/w) Total acids (% w/w) Browning units/100 g bone dry wood 1. Fluidized bed (500ºC, 0.5 s) 2. Fast thermal processes (600ºC, 0.2 s) 3. Commercial liquid smoke % w/w - Wt% of product yield from dry wood feedstock determined from the water soluble fraction

As can be seen from Table 1, the yield of carbonyls is approximately three times greater when liquids produced by fast pyrolysis processes are used than with commercial liquid smoke, while the yield of phenols is more than doubled, the yield of acids is improved, and the degree of browning is approximately six times greater.

The level of benz[a]pyrene in the liquids from fast pyrolysis is, prior to dilution and phase separation, at least an order of magnitude lower than that of liquids produced by known commercial processes. This lower level of benz[a]pyrene allows a more concentrated product to be produced. The total condensate from conventional pyrolysis contains approximately 750 ppb of benz[a]pyrene.

The content of benz[a]pyrene in the total condensate from the fast pyrolysis is between 5 and 50 ppb.

After dilution and phase separation, the ratio of carbonyls to phenols is higher in rapid pyrolysis, which is characteristic of the high browning ability in relation to the level of seasoning power. In addition, the yields of the undesirable by-products are lower and the corresponding costs are lower.

Unconcentrated commercial liquid smoke has a browning level between 3.0 and 13. While processes are available to concentrate liquid smoke to achieve a browning level of up to 25, unconcentrated liquid smoke has a practical upper limit of about 13, since benz[a]pyrene levels become very high when the liquid smoke is further concentrated in the water collection bath beyond this level.

By using rapid pyrolysis processes, browning levels of up to 45 can be achieved without any concentration steps and benz[a]pyrene contents of less than 0.5 ppb.

The presence of hydroxyacetaldehyde can be used as a measure of the value of the liquid for smoke coloring applications. The yield of this compound in fast or flash pyrolysis processes increases with decreasing temperature from 900 to about 500°C and decreasing residence time. Yields of hydroxyacetaldehyde in excess of about 8 mass% can be obtained at a reaction temperature of 550 or 600°C and a vapor residence time of 100 ms.

The yield of hydroxyacetaldehyde is much higher in fast pyrolysis processes. A comparison of the yields of hydroxyacetaldehyde from two fast pyrolysis processes and in commercial liquid smoke is shown in Table 2. As can be seen, yields of up to approximately four times the amount are achieved in fast pyrolysis. Hydroxyacetaldehyde is one of the predominant carbonyls in the wood pyrolysis liquids and is therefore used as a measure for liquid smoke applications. Table 2: Chemical analysis of pyrolysis liquids (hydroxyacetaldehyde yields) Sample source Hydroxyacetaldehyde yields (% w/w) 1. Fluidized bed (450 to 550ºC, 0.5 s) 2. Fast thermal processes (550 to 700ºC, 0.2 s) 3. Commercial liquid smoke less than 2

Hydroxyacetaldehyde (glycoaldehyde) and acetol (1-hydroxy-2-propanone) are the two predominant carbonyls in pyrolysis fluids. Hydroxyacetaldehyde is more reactive with respect to browning and its presence is an excellent measure of the browning ability of the fluid. Acetol does not brown much. The concentration ratio of hydroxyaldehyde to acetol can therefore be used as a measure of the effectiveness of the carbonyls in fluids with respect to browning ability.

The analysis shows that the concentration ratio of hydroxyacetaldehyde to acetol in conventional liquid smoke is less than 1.0. However, the average ratio (4 samples) of hydroxyacetaldehyde/acetol in fast pyrolysis liquids is approximately 6 (5.9), while the maximum measured ratio is 7.2. It follows that not only are more carbonyls produced in fast pyrolysis (i.e. higher yields), but that the carbonyls produced are more effective tanning agents.

The parameters that should be optimized in any rapid pyrolysis process to produce a suitable liquid product to be used as liquid smoke include:

1) high heating rates of the wood-based product (more than 1000ºC per second)

2) a vapor residence time (i.e. the average time the gas/vapor phase remains in the reactor) of more than (0.15 seconds and less than 1.0 seconds, preferably less than 0.6 seconds;

3) reactor temperatures in the isothermal reaction between 400 and 800ºC; and

4) quenching the liquid/vaporous product to a temperature of less than 300ºC in less than 0.6 seconds to achieve high yields of liquids.

When a vacuum apparatus is used for pyrolysis, the heating rate of the wood or cellulose is much slower than with a fast thermal process apparatus or a fluidized bed reactor. However, secondary pyrolysis reactions are reduced by rapidly removing and cooling the primary pyrolysis vapors. Thus, the rapid heating rate is not so critical as long as the secondary reactions are suppressed.

The main components of rapid pyrolysis processes are capable of both reaching a very high temperature in a minimal amount of time and having a relatively short residence time at these temperatures to effect pyrolysis of the wood or cellulose. This short residence time at a high temperature is achieved by many systems. One process is a vacuum pyrolysis process based on the principle that primary products can be entrained from the reactor under vacuum conditions before they have a chance to react further and form secondary pyrolysis products. This process is described in Fundamentals of Thermo-Chemical Biomass Conversion, R.P. Overend et al. (Editors) Elsevier Publishers, (1985) in an article entitled "Pyrolysis under Vacuum of Aspen Poplar" by Christian Roy, Bruno de Caumia, Dominique Brouillard and Hughes Menard, the contents of which are expressly referred to here.

The solid wood feedstock remains in the reactor until it has completely reacted. A total liquid yield of 68-74 wt.% of the mass of the total wood feedstock is reported at reaction temperatures of 450ºC, a solid heating rate of 10ºC/min and a residence time of up to 2 seconds. With a steam residence time of approximately 2 seconds, the char yields are between 16 and 20 wt.% of the mass of the wood feedstock.

A second method for fast pyrolysis is "flash" pyrolysis, which uses a fluidized bed reactor system and operates at temperatures between 400 and 650ºC. Total liquid yields of between 60 and 70% of the wood feedstock are obtained with an average residence time of 0.5 seconds. Char yields are typically between 10 and 20% of the wood mass. Residence times of up to 3.0 seconds can be achieved. See "Production of Liquids from Biomass by Continuous Fast Pyrolysis" in Bioenergy 84 vol. 3, Biomass Conversion; D S. Scott and J. Piskorz, the contents of which are incorporated herein by reference.

A third process is a fast pyrolysis process that uses hot particulate solids and/or inert gases to rapidly transfer heat to the carbonaceous feedstocks in a reactor system (Fast Thermal Pyrolysis). This results in very high yields of liquid or gas from biomass, depending on the reactor conditions. Char yields range from 0 to 6%, depending on the feed, reactor temperature and residence time. Maximum gas yields are 90% of the mass of the feed at 900ºC and maximum liquid yields are 85% of the mass of the feed at 600-650ºC. This apparatus can be operated between 350 and 1000ºC with residence times between 0.030 and 3.0 seconds. An apparatus for rapid thermal pyrolysis is described in "Characterization Of Solids Mixing In An Ultra-Rapid Fluidized Reactor", by Berg et al., presented at the Powder and Bulk Solids Conference, Rosemont, Illinois, May 12-15, 1986.

Each of these rapid pyrolysis processes, where applicable, offers significantly improved yields and better quality liquid and gaseous products compared to conventional pyrolysis systems.

Short description of the drawings

Details of the embodiments of the invention are described with reference to the accompanying drawings.

Fig. 1 is a schematic representation of a flow system for rapid pyrolysis, known as a fast thermal process.

Fig. 2 is a top view of the reactor of the pyrolysis apparatus of Fig. 1.

Fig. 3 is a section along the line III-III in Figure 2.

Fig. 4 is a graphical representation of product yield in mass percent as a function of residence time in milliseconds.

Fig. 5 is a graphical representation of the yields of hydroxyacetaldehyde as a function of reactor temperature.

Fig. 6 is a graphical representation of the yields of hydroxyacetaldehyde as a function of residence time at different temperatures.

Detailed description of the preferred embodiments

In the following description, corresponding elements shown in each figure of the drawings will be designated by the same reference numeral.

Although the accompanying drawings and description refer to the Fast Thermal Pyrolysis process, corresponding products can also be obtained with vacuum and flash pyrolysis systems, and also with other systems that provide high temperatures with a limited residence time.

The main components of the rapid thermal process are shown in Fig. 1. Rapid mixing and heat transfer are accomplished in two vessels. The first vessel (1) or thermal mixer allows heat to be transferred to the wood from hot particulate solids or gases, which may consist of gaseous nitrogen, suspended particulate solids, or a combination of both. In the second vessel (9), the quenching vessel, the products may be quenched to reduce secondary reactions of the initially formed pyrolysis products.

Figures 2 and 3 show that the thermal mixer (1) has opposing, merging inlets (3) for the solid heat carrier. The system effectively destroys the angular momentum of the heat carrier by causing violent turbulence. Pulverized wood feedstocks are then fed through a cooled pipe (4) over the top of the thermal mixer (1) to the turbulent region where they are mixed within 30 milliseconds.

After heating and mixing, the wood or cellulose and the primary vapors from pyrolysis remain at the reaction temperature for between 0.03 and 2.0 seconds, depending on the desired products. The primary pyrolysis vapors are generated once the wood or cellulose has been heated sufficiently to initiate the pyrolysis reactions.

The hot gaseous product is rapidly cooled (i.e. in less than 30 milliseconds) by the addition of a single tangential jet of very low temperature nitrogen (5). Mechanical table feeders are used to feed wood to the reactor system. The solids flow from sealed hoppers (6) (containing a sufficient amount of wood or particulate solids) through a double hopper system and are metered through these onto a rotating table. Two fixed baffles sit near the surface of the rotating table and force the solids over the outer edge. From the table the solids then fall into a conical chamber where they are picked up by the carrier gas, nitrogen, and entrained into the transport line. The rough range in which the biomass or particulate solids feeding rate is to be adjusted is selected by leaving a gap between the lower hopper and the table. Exact control is achieved by the rotation speed of the table.

When particulate solids are required to supply the process heat, the feeders (7) pass hot particulate solids through a non-mechanical high temperature valve operating at reaction temperature. These hot solids are then passed to the thermal mixer (1).

The solid particulate carbonaceous feed (or atomized carbonaceous liquids) is then injected axially through a water or air cooled tube (4) into the turbulent region of the reactor (1) where it is effectively mixed and rapidly heated to at least 400ºC within 0.10 seconds, preferably within 0.03 seconds.

The rapid pyrolysis of wood is initiated in the thermal mixer (1) and continued in a transport reactor (9). The transport reactor consists of a length of pipe located in an electric furnace (10). The mixture of hot gases and biomass flows from the thermal mixer (1) through the transport reactor (9) into the quench vessel (2) and the solids separator (23). By changing the reactor volume and the ratio of the flow rate of heat carrier and biomass, the residence time can be varied between 0.03 and 3.0 seconds. Reactor temperatures can be in the range of 400 to 1000ºC, preferred temperatures are between 400 and 800ºC and particularly preferred temperatures are between 500 and 600ºC. The achievable heating rate of this device is more than 1000ºC per second.

A powerful cyclone cooler (25) improves the yield of the recovered liquid products. In addition, an electrostatic precipitator (24) can be installed in the downward gas line to recover additional liquid products.

Although only the apparatus for the Fast Thermal Process is described here, the invention, as defined by the following claims, is intended to cover any use of the products of a fast pyrolysis process for flavoring by liquid smoke.

The wood feedstock can be any suitable wood product, but red maple is preferred. The feedstock should be ground to a 100-500 µm fine powder and then dried before use as the pyrolysis feedstock.

After the condensates have been collected, water is added to cause phase separation to reduce the content of benzo[a]pyrene and tars. The amount of water added in excess of that required to cause phase separation is discretionary. The more water added, the greater the separation of higher molecular weight components. Water can be added to a desired level in excess of that required to cause phase separation to achieve a desired level of browning.

For use with Vienna sausages, solutions with browning levels down to approximately 3 are suitable to produce a desirably smoke-flavored and colored product. In some markets where darker, more heavily smoked products are preferred, aqueous smoke solutions with a browning index of at least 20 are routinely used for flavoring.

When the preferred method of application is atomization, it is sometimes difficult to achieve sufficient smoke coloring of the meat. In these cases, smoke solutions are used for flavoring with browning levels of up to 30. The amount of water added to the condensates of this invention to produce a solution suitable for application to meat and other foods depends on the effect desired by the operator.

Commercially available liquid smoke has browning levels that range from a minimum of 3 to a practical upper limit of about 30. This upper limit is due to the limitations of conventional processes for producing liquid smoke. Conventional processes collect the water-soluble condensates in a water bath. The browning level should be kept below 13 to reduce the benz[a]pyrene concentration. A browning level above 13 is achieved by subsequent concentration. Consequently, it is becoming increasingly difficult and expensive to produce a smoke solution with a browning level above 13. The difficulties and high costs of concentration set a practical upper limit of 30, while solutions with higher browning levels would be useful. On the other hand, if solutions with browning levels of 30 or more were readily available commercially, they could be used particularly in atomization or as a starter for sausage casing applications such as in U.S. Patent 4,504,501. By adding little or no water to the condensates of the present invention, solutions with very high browning levels can be prepared without the need or expense of further concentration.

example 1

A general summary of the results of a fast pyrolysis run at 650-800ºC in the fast thermal process apparatus using red maple as the feed and nitrogen as the heat transfer medium is shown in Table 3. The apparatus used for these results is fed with 300 g of feed per hour. The char and gas yields are from direct measurements and the liquid yield is from a difference calculation. However, these liquid yields are very close to the actual liquid yields as confirmed by mass balance. All percent mass yields in Table 3 are on a bone dry feed basis. The results clearly show that the char yields are significantly lower and the liquid yields are significantly higher than the corresponding yields from conventional slow pyrolysis processes. Table 3: Summary of mass balances from red maple pyrolysis experiments Run Number Temp. (ºC) Residence Time (ms) Gas Yield (%) Condensed Liquids Residual Liquids (%) Char (%) Total Recovery (%) Note: - Where no condensed liquids are shown (no values listed), the residual liquids represent the complete liquid sample. - These results are on a "feed" basis.

Example 2 Operation of process equipment for rapid thermal pyrolysis and the results Operating parameters:

- The experiments are carried out using poplar wood chopped to approximately 300-10⁻⁶m (300 µm).

- The moisture content of the wood is approximately 1% (moisture basis).

- Wood is fed at a rate in the range of 3 to 5 kg/h.

- The reaction temperatures are in the range of 400 to 650ºC.

- The residence times of the steam are normally in the range of 600-1200 milliseconds (ms).

- The heat transfer medium consists of quartz sand with an average particle size of approximately 150 10⁻⁶m (150 µm) and is transported by inert nitrogen gas.

Device and operating procedure:

Rapid thermal process equipment of the type shown in Figure 1, Figure 2 and Figure 3, using hot particulate sand as the heat source, is used to produce liquid smoke. The equipment is designed to feed 5 kilograms of feed per hour. Three heat transfer fluid feeders are used to heat the sand heat transfer fluid and transfer it to the transfer lines. Each feeder is approximately 1.2 meters long, has an external diameter of 150 mm and can hold 30 kg of quartz sand. The maximum feed rate is approximately 60 kg per hour (for each feeder) and the maximum heat transfer fluid temperature is 1100ºC. The feeder is controlled by a flow tube and a non-mechanical high temperature "J" valve.

The poplar wood is air dried, ground and a mean particle size of approximately 300 10⁻⁶m (300 µm) is separated. It is then oven dried before being fed into the biomass feeder. The feeder has a capacity of approximately 4 kg. Feeding rates can be varied between 0 and 10 kg per hour and are independent of the flow rate of the transport gas and the flow rate of the solid carrier.

The wood feedstock is fed from the "biomass feeder" to the top of the reactor where it is injected into the cloud of turbulent hot solids. Extremely rapid heating of the feedstock can be achieved when the feedstock and the hot sand particles are rapidly and thoroughly mixed. After the rapid, thorough mixing is complete, the feedstock and solid heat carrier flow through a tubular transport reactor, the length of which is designed to determine the processing residence time. The reactor system consists of a fast thermal mixer and two lengths of transport reactor. Each of these components is located in its own furnace with independent temperature control. The feedstocks are rapidly mixed with the solid heat carrier (i.e. sand) located in the fast thermal mixer. Chemical reactions can then be carried out in the transport reactor sections. The first reactor is 1.2 m long, while the second is 0.6 m long. The reactor system components are made of Sch 40 Inconel 601 (40 mm internal diameter/1.5" nominal).

After the hot solids (coal/sand) have been recovered in a "receiver" or separator vessel, the products are rapidly cooled in the transfer line. They are additionally cooled in main (water cooled) and secondary (dry ice/acetone cooled) coolers, which also condense vapors and recover liquids. The solids receiver vessel is an inertial separator made of stainless steel and can hold approximately 100 kg of hot solids. Separation of gases from the solids is based on the lower moment of inertia of the gas/liquid product (in Compared to the hot sand), which can change direction more suddenly than the solids and escape into the transfer line to be directly quenched with nitrogen gas.

The main cooler is a water-washed mild steel line (which has both an internal and external water jacket) and is coated with a chemical resistant paint. The cooling water enters at approximately 19ºC and cools the product to approximately 35ºC.

The secondary cooler is also a lined mild steel line that is not jacketed but sits directly in an insulated acetone/dry ice bath. It has a tangential gas/vapour inlet that directs the products against the cooler wall where efficient heat transfer can take place. The secondary unit provides a gas outlet temperature of approximately -5ºC.

Parallel filters are used to capture low volatile aerosols. The clean gas is then passed through a jet meter to determine the flow for the final mass balance. A portion of the product gas is continuously bled from the main stream into a gas sample container for subsequent analysis. The three parallel filters are made of stainless steel, have a pore size of 0.5 10-6m (0.5 µm) and are housed in a single filter housing. Each of these units has an (external) diameter of 50 mm and is approximately 0.5 m long. After a run, the coolers, filters and transport lines are washed with acetone, the solution is filtered and the acetone is evaporated under vacuum to obtain the liquid product. The coal is determined by ashing a few representative samples of the coal/sand mixture recovered from the solids separator. The gases are analyzed by standard gas chromatography techniques. The results of several typical runs are shown in Table 4. Table 4: Summary of mass balance for pyrolysis experiments with poplar wood Run number Temp. (ºC) Time (ms) Product yields (% of wood feed) Gas Liquid Coal

Example 3 Fluidized bed operation and results Fluidized bed operation: Operating parameters:

- Experiments are carried out using paperboard wood crushed to approximately 595 10⁻⁶m (595 µm) (30 mesh).

- The moisture content of the wood is approximately 6% (moisture basis).

- Wood is fed at a rate in the range of 1 to 2.5 kg/h.

- The reaction temperature (in the fluidized bed) is in the range of 400 to 650ºC.

- The residence times of the steam are normally in the range of 500-700 milliseconds (ms).

The fluidized bed consists of quartz sand with an average particle size of approximately 720 10⁻⁶ (720 µm).

The recovered product gas (mainly CO, CO2 and CH4) is used to swirl the sand and transport the wood feedstock into the reactor.

Device and operating procedure:

The poplar wood (or other wood species, straw or peat) is air dried, ground and a mean particle size of approximately 595 10⁻⁶m (595 µm) separated by sieving.

The prepared wood is transferred at variable speed from a hopper into a twin-screw feeder and fed into a stream of recovered product gas. It is then transferred directly to the fluidized bed section of the fluidized bed reactor.

The reactor layer consists of very uniformly spherical Ottawa quartz sand, which has a mean particle size of approximately 720 10⁻⁶m (720 µm).

The fluidizing gas (mainly CO, CO2 and CH4) is preheated in the feed line by electrical heaters and enters the fluidized bed through a porous stainless steel plate at a velocity 1.2 - 2 times the minimum fluidizing velocity.

The reactor is wrapped with heating coils for additional heating.

Pyrolysis products and recovered gases are fed from the top of the reactor into a cyclone where the dry coal is removed from the gas/vapour phase. The gases and vapours are then passed into two coolers and then through a series of filters.

The first cooler is normally operated at 20ºC, while the second is maintained at 0ºC. The filter stack consists of a 5 10⁻⁶ m (5 µm) mesh screen in a row with a subsequent filter vessel packed with glass wool.

After a run, the condensers are washed with acetone, the solution is filtered and the acetone is evaporated in vacuo to obtain the liquid product. The filters are weighed before and after the experiment and the contents recovered if the amount is significant. Charcoal is collected in a charcoal jar (at the cyclone exit) and weighed. Gases are analyzed by standard gas chromatography methods. The results of several runs over a temperature range of 425 to 625ºC are presented in Table 5. Table 5: Results from fluidized bed experiments: Fast pyrolysis of poplar wood Temp. (ºC) Residence time (ms) Product yields (% of wood feed) Gas Liquid Coal Total recovered (%)

The values in parentheses are the total organic liquid content (i.e. excluding moisture). The difference is moisture (water) in the liquid sample.

Similar experiments have been carried out with maple and spruce with similar yields of coal, gas and liquid.

As is evident from the data in Tables 3, 4 and 5, the preferred operating temperature is in the lower ranges with a relatively short residence time of 300-600 ms. However, good yields are achieved over the entire operating range of the fast thermal pyrolysis apparatus and at different residence times. As Figure 4 shows, the shorter the residence time that can be achieved, the higher the yields of the preferred liquid product.

As mentioned above, the yield of hydroxyacetaldehyde is a good measure of the browning ability of the liquid smoke. In Figures 5 and 6, yields of this compound are plotted against reactor temperature and residence time. Figure 5 is a plot of hydroxyacetaldehyde yields from the fast pyrolysis of wood against temperature.

Figure 5 confirms that the optimal reaction temperatures are between 500 and 600ºC. Figure 6 also confirms that the optimal conditions are between 500 and 600ºC with a short residence time.

Example 4

A sample of the liquid pyrolysis product from the fluidized bed reactor referred to in Example 3 is diluted with water in the following proportions. The water-soluble fraction is separated and analyzed. Table 6: Dilutions of liquids from fast pyrolysis Wt.% of liquids from fast pyrolysis in the total solution Acids % wt. Phenols % wt. Carbonyls % wt. Units of browning degree Specific gravity 21º Benz[a]pyrene ppb

These results demonstrate that it is advantageous to add enough water to cause sufficient phase separation to reduce the benz[a]pyrene content to less than 0.5 ppb. As can be seen from Tables 7 and 8 below, the resulting solutions have significantly higher carbonyl concentration to phenol concentration and browning to phenol concentration ratios than commercially available solutions prepared by slow pyrolysis processes. Table 7: Relationship between carbonyl concentrations and browning level and phenol concentrations Weight % of liquids from the total solution Browning level Carbonyls/Phenols Browning level/Phenols Table 8: Average of ten representative ratios in liquid smoke solutions of rapid pyrolysis Acid Concentration % w/w Browning Degree Carbonyls/Phenols Browning Degree/Phenols

As can be seen from both Table 7 and Table 8, the ratios are larger in more dilute solutions. This is because the solubility of carbonyls remains the same regardless of the concentration, while phenols are less soluble in more dilute solutions. Consequently, The advantage of water addition during rapid pyrolysis is to reduce the phenols, thereby reducing the flavor while maintaining a high browning potential, and to reduce the solubility of benz[a]pyrene to less than 0.5 ppb.

As shown by comparing the data in Tables 7 and 8, the ratios of carbonyl concentrations to phenol concentrations and browning level to phenol concentrations for an identical browning level are significantly higher for liquids from rapid pyrolysis than for conventional liquid smoke. The higher ratio for rapid pyrolysis products results in a darker product for a given aroma intensity. This allows for coloring foods with a lower smoke aroma or, in the other case, a darker product with a comparable aroma intensity.

The lowest browning level used for smoking meat is approximately 3.0. This browning level is used for direct application to food. Based on the above results, the product from rapid pyrolysis could be diluted to a 6.1 wt% solution and still have a browning level above 3.0.

Example 5 Results of using liquids from rapid pyrolysis on Vienna sausages 1. Committee for testing colour/tanning

Approximately 2.5 lb strands of skinless Vienna sausages obtained from Cher-Make Sausage Co. (Manitowoc, WI) were immersed for 60 seconds in the following liquids:

A. Water (comparison)

B. A 10 wt.% solution of a liquid from a rapid pyrolysis (fluidized bed)

The Vienna sausages were heated to an internal temperature of 70ºC according to the following scheme:

- 10 minutes at 43.3ºC

- 45 minutes at 60.0ºC

- 25 minutes at 71.1ºC

- and at 82.2ºC until the internal temperature reached 70ºC.

After heating, the Vienna sausages were placed in a cooler at 4.4ºC overnight for subsequent evaluation and examination.

The following day, the Vienna sausages were peeled and a panel of nine assessors were asked which row showed the most appealing brown color. All nine stated that sample B was noticeably browner than the control sample submerged in water (and therefore more appealing).

The results demonstrate the ability of aqueous solutions of liquids from rapid pyrolysis to react with meat surfaces to produce the desired smoke appearance.

2. Taste comparison committee

Approximately 2.5 lb strands of skinless Vienna sausages obtained from Cher-Make Sausage Co. (Manitowoc, WI) were immersed for 60 seconds in the following liquids:

A. A 10 wt.% solution of a liquid from a rapid pyrolysis (fluid pyrolysis)

B. A solution prepared from liquid smoke from slow pyrolysis according to U.S. Patent 3,106,473 and having a browning index of 3.9.

The Vienna sausages were heated to an internal temperature of 70ºC according to the following scheme:

- 10 minutes at 43.3ºC

- 45 minutes at 60.0ºC

- 25 minutes at 71.1ºC

- and at 82.2ºC until the internal temperature reached 70ºC.

The following day, a panel of nine assessors was asked to examine the Vienna sausages that had been peeled and heated to 49ºC. A triangular procedure (i.e., three samples were used, two of which had received the same treatment and one the other) was used to assess whether the panel members could distinguish between the two treatments.

The results show that only one of the nine members could detect a difference between the aqueous solutions of the liquids from the rapid pyrolysis and conventional flavoring smoke solutions when they were used on Vienna sausages. This is not statistically significant and shows the usefulness of the invention in smoking meat.

Claims (10)

1. Process for the preparation of an aqueous smoke solution for use in foodstuffs comprising: a) Heating wood pulp or cellulose in the absence of oxygen to a temperature between 400 and 650ºC within one second; (b) maintaining the wood or cellulose together with the pyrolysis products formed from the wood or cellulose at a temperature of between 400 and 650ºC for a period of between 0,03 and 2,0 seconds; c) lowering the temperature of the pyrolysis products to below 350ºC within 0.6 seconds to obtain a liquid extract; and d) Isolating the liquid extract. 2. Process according to claim 1, in which the wood or cellulose and the pyrolysis products are kept between 400 and 650ºC for a period of between 0.03 and 0.6 seconds. 3. A process according to any one of claims 1 and 2, in which the liquid extract has a ratio of hydroxyacetaldehyde concentration to acetol concentration greater than 5.5 to 1. 4. A process according to any preceding claim, in which the liquid extract has a ratio of browning to phenol concentration greater than 8.9 to 1. 5. The process of claim 2 wherein the resulting liquid extract is separated, combined and diluted with water to achieve partial phase separation and to obtain an aqueous solution having a benz[a]pyrene concentration of less than 1.0 ppb, a ratio of browning to phenol concentration greater than 8.9 to 1 and a ratio of hydroxyacetaldehyde concentration to acetol concentration greater than 5.5 to 1. 6. Liquid smoke solution obtained from rapid pyrolysis with an aqueous solution obtained by a method according to any of the appended claims having a benz[a]pyre concentration of less than 0.5 ppb. 7. A process for seasoning and colouring foodstuffs, which comprises: a) heating wood pulp or cellulose in the absence of oxygen to a temperature of at least 400ºC within one second; (b) maintaining the groundwood or cellulose and the pyrolysis products formed from the wood or cellulose at a temperature of at least 400ºC for a period of between 0.03 and 2 seconds; c) reducing the temperature of the pyrolysis products to at least 300ºC within 0.6 seconds to obtain a liquid extract; d) isolating the liquid extract; and e) bring the wood into contact with the liquid extract. 8. A process according to claim 7, in which the liquid extract has a benz[a]pyrene concentration of at least 0.05 ppb. 9. A food product comprising a proteinaceous food substrate flavored with a liquid extract, prepared by a process according to any one of claims 1 to 4. 10. Food product according to claim 9, in which the food substrate is selected from the group meat, poultry or fish.