IE42727B1 - Instant milk process and product - Google Patents

Abstract

1520592 Instant milk powder FOREMOST McKESSON INC 24 May 1976 [2 June 1975] 21466/76 Heading A2B An instant milk, powder is made by supplying to an agglomerating chamber (i) dry milk powder (ii) an atomized fat-water emulsion, (iii) atomized lecithin such that the powder particles are moistened and caused to stick together and form agglomerates with the lecithin and fat being distributed on the particles and drying the agglomerates to remove excess moisture. The fat-water emulsion may be subjected to high pressure homogenisation and contain an emulsifier, suitably a mono- or diglyceride of a long chain fatty acid.. The emulsifier may also contain non-fat milk solids and prior to homogenization be subjected to a temperature of 170-190‹F for 6-15 mins.

Description

This invention relates generally to processes for the commercial manufacture of fat-containing dry milk or flavored dry milk in the form of aggregates which can be readily dispersed in water to form a stable reconsti5 tuted milk. Also it pertains to products resulting from such processes.

So-called instant dry milk is widely manufactured and sold in the United States and other countries. As disclosed in U.S. Patent 2,835,586 the process involves supplying nonfat anhydrous dry milk powder to an agglomerating chamber where the particles are moistened and commingled to cause formation of random porous aggregates These aggregates, which in typical instances may have a total moisture content of the order of from 10 to 15%, are then subjected to secondary drying to remove excess moisture. Such instant nonfat dry milk can be readily reconstituted with cold water by simple stirring and without vigorous agitation. The process of said Patent 2,835,586 can be used to agglomerate spray dried fat20 containing dry milk as well as spray dried nonfat dry milk powder. However, instant fat-containing milk made in this fashion has impaired wettability and dispersibility in water, and the reconstituted milk is subject to fat separation.

Subsequent to the development of the above process, it was found that an acceptable fat-containing agglomera- 3 42737 ted dry milk could be formed by the use of lecithin.

As described in U.S. Patent 3,164,473,lecithin is supplied in such a fashion that in the final agglomerated product, it is in the form of extraneous lecithin distributed on the powder particles and agglomerates.

The use of lecithin as described in said Patent 3,164,473 makes it possible to produce a fat containing instant dry milk which can be re-constituted in cold water. However, it makes use of fat-containing spray dried milk powder as a source material. An improved process making use of the process of U.S. Patent 3,164,473 is disclosed in U.S. Patent 3,300,315. The improved process likewise makes use of fat-containing milk as a source material. The liquid fat-containing milk is spray dried to form a moist powder which is passed through an agglomerating chamber into which a mixture of steam, water and lecithin is introduced. The resulting aggregates, after removal of excess moisture, having relatively good dispersibility in cold water.

The processes of Patents 3,164,473 and 3,300,315 have been used for the commercial manufacture of acceptable instant dry milk products having a fat content of the order of 5%. However, plants using such processes require high capital investment in central locations (e.g., for evaporators, spray dryers, and instantizers and involve high transportation costs when the product is distributed nation-wide.

U.S. Patent 2,911,300 proposes to produce a dry instant milk product containing fat by first forming nonfat milk solids in the form of aggregates, and after drying to remove excess moisture, fat in molten form is applied to the surfaces of the aggregates. As pointed - 4 out in said Patent 2,911,300, such a product can be dissolved in warm water. The patent further proposes the use of a fat-water emulsion of the type disclosed in U.S. Patent 2,622,984 whioh consists of fat and water together with a soluble caseinate. This mixture is subjected to homogenizing as ordinarily applied in the milk industry, after which it is applied to the aggregates and the aggregates dried to remove excess moisture. Patent 2,911,300 also refers to the use of lecithin as an emulsifier in preparing the emulsion of Patent 2,622,984, in place of part or all of the caseinate content. While the process of Patent 2,911,300 makes use of nonfat milk solids as a source material, it separates the aggregating step from the step of applying the fat emulsion. Since some moisture is added with the fat, the moisture content of the aggregates is increased, thus requiring another stage of secondary drying. This process is subject to other difficulties, particularly in that some fat separation tends to occur in the reconstituted milk, and the amount of separating fat increases for the higher fat contents.· In general the present invention relates to a process for the manufacture of fat-containing instant dry milk which carries out an agglomerating operation and the application of fat in a single step.

In general, the process of the present invention involves supplying an anhydrous dry milk powder, such as is produced by spray drying, to an agglomerating chamber. The powder while dispersed within the chamber is commingled with atomized material which is prepared by homogenizing a mixture containing fat and water, preferably in the presence of one or more agents which protect the fat globules against reversal of the emulsion phase. Xn addition to atomizing and dispersing the fat emulsion in the agglomerating chamber, lecithin is likewise dispersed in the chamber and commingled with the powder particles. The powder particles are thereby caused to adhere together in the form of porous random aggregates, with the fat and lecithin being distributed on the powder particles and the aggregates, simultaneously with the agglomerating operation. The moist material discharging frcm the agglomerating chamber is subjected to further drying for the removal of excess moisture.

In one aspect of the process high pressure homogenization is employed to prepare a fat emulsion having relatively small fat globules of less than 3 microns, the homogenization being under such conditions as to minimize reversal of the emulsion phase (i.e., demulsification) with resulting fat churning.

In a further aspect of the invention an instant fat-containing dry milk is produced which has its fat content in the form of relatively small globules of micron si2e and intimately associated with the aggregates, with the lecithin being incorporated in such a manner as to be- effective in promoting wettability and dispersibility of the product.

Additional objects and features of the invention will appear from the following description in which the preferred embodiments have been set forth in detail in conjunction with the accompanying drawings in which:Figure 1 is a diagram illustrating one procedure for carrying out the process.

Figure 2 is a diagram illustrating another 4273’ - 6 procedure for carrying out the process.

Figure 3 schematically illustrates suitable apparatus for carrying out the process.

Figure 4 schematically illustrates apparatus for preparing material that is supplied to the agglomerating chamber, and the means associated with the agglomerating chamber for dispersing material into the agglomerating chamber.

The process as illustrated in Figure 1 makes use pf anhydrous spray dried milk powder as the source material, and dairy cream as a source of fat. Dairy cream normally contains water, fat, protein and some lactose. The water content may vary from 54 to 58%, the fat from 38 to 42%, the protein from 2 to 2.5%, and the lactose from 2.8 to 3.4%. A typical cream is an emulsion containing about 56% water, 39% fat, 2.2% protein, and 3.1% lactose, with an ash content of about 0.4%. Before subjecting the cream to homogenizing step 11 to reduce the size of the fat globules, it preferably is mixed in step 10 with one or more agents which serve the purpose of preventing reversal of the emulsion phase with fat churning under relatively high homogenizing pressures. Agents which have been found suitable for this purpose are certain emulsifiers having such characteristics that they will not impair the flavor and quality of the final product. Satisfactory emulsifiers are those selected from the group comprising mono and diglycerides of long chain fatty acids, and ethoxylated mono and diglycerides of long chain fatty acids, or combinations thereof having a melting point below 180°F. (e.g., within the range of 85 to 180°F.)· In practice, we have obtained good results by using a - 7 mixture of from 10 to 25% (optimum 17%) of distilled mono-glycerides and from 90 to 75% (optimum 83%) of ethoxylated mono and diglycerides at a level of from 1 to 3% (optimum 1.5%) of the butterfat. These materials together with the cream are blended at a temperature (e.g., 180°F.) above the melting point of the emulsifiers.

An additional material which serves in conjunction with the emulsifier to prevent reversal of the emulsion phase in the homogenizing step 11 is nonfat milk solids, which can be added to the cream in step 10 as indicated. The amount of nonfat milk solids added at this point is in accordance with the fat content of the cream. It may range from an amount (by weight) equal to the amount of fat, to one fourth the amount of fat.

Introduction of milk solids in step.10 for mixing with the cream can be facilitated by first dispersing the milk solids in water and then blending the resulting reconstituted milk with the cream. For example, the amount of milk solids dispersed in water can be such ac to provide a concentrate consisting of 40 to 50% solids. The total amount of moisture in the mix should be consistent with the moisture requirements for the agglomerating operation.

For the purpose of promoting storage stability, small amounts of an antioxidant may be added to the cream, based on the fat content. The cream may also serve as a carrier for nutrient fortification, as for example, such nutrients as vitamins A and D.

The mixture produced in step 10 at a temperature of 145 to 150°F. is supplied to the homogenizing step - 8 11 where it is homogenized at relatively high pressures, such as at a pressure of at least 2500, more preferably 2500 to 3500, psig for the first stage and 500 psig for the second stage. Homogenization at such pressures serves-to greatly reduce the size of the fat globules whereby the bulk of the globules have a size of less than 3 microns. Normally the use of such high homogenizing pressures tends to reverse the emulsion phase with release of free fat and fat churning. However, when the emulsifier is present it appears that this phase reversal does not take place or is minimized, and therefore there is a minimum amount of free fat in the homogenized material. Nonfat milk solids present in the mixture also play a part in preventing such phase reversal. According to our observations this is due to association of the protein content of the nonfat milk solids with the enrobement of the fat globules.

After being homogenized in step 11, the fat emulsion mixture is supplied to the agglomerating. step 12 where it is dispersed in atomized form and the atomized droplets caused to commingle with particles of dry milk powder being continuously supplied to the agglomerating chamber. A spray dryer type of atomizing nozzle can be used, with the fat emulsion mixture being supplied to the nozzle at pressures of from 1500 to 4000 psig (2000 psig optimum). Water vapor and steam are likewise dispersed in the agglomerating chamber whereby sufficient moisture is present in the agglomerating chamber to cause moistening of the powder particles with agglomeration of the particles together. In the agglomerating step the atomized and agglomerated fat mixture becomes intimately associated with the powder particles and the resulting aggregates.

I Lecithin, as is or in the form of a product containing lecithin, is supplied to provide a wetting agent which increases wettability and dispersibility of the final product in cold water. It is introduced into the agglomerating step 12, separate from the homogenized fat mixture. For example as indicated in Figure 1, the lecithin may be supplied to a mixing device 13 where it is intermixed with steam being sup'~ lied to the agglomerating chamber. When introduced in this manner the lecithin maintains its effectiveness in promoting wettability and dispersibility of the final product. When lecithin is mixed or homogenized with milk protein such as is present in cream and nonfat milk solids, the protein tends to enrobe the lecithin, thus blocking its wetting abilities.

The agglomerating step can be carried out in an agglomerating chamber of the type disclosed in said U.S. Patent 2,835,586, or equipment as disclosed in U.S.

Patent 3,311,306. The aggregates discharging from the agglomerating chamber in a typical instance have a total moisture content ranging from 9 to 14% (11 to 12% optimum). A substantial part of this moisture is derived from the cream mixture, and the remainder may be derived from the condensed steam. The final or secondary drying step 14 can be carried out by the procedure described in said Patent 3,300.315 to produce a final dry product of the desired moisture content (e.g., 1 to 2%).

As pointed out in said Patent 3,300,315, lecithin is is the commercial or popular name for a crude mixture of 42737 - 10 compounds which may be more accurately designated as phosphatides or phospholipids. The phosphatides are complex organic compounds which are similar to fats or lipids but differ from fats radically enough to give them unique properties. Lecithins of vegetable oil origin are mixtures Of phosphatides produced from such raw materials as cottonseed oil, corn oil, or soybean oil. Products from current commercial treatments which modify natural· lecithin to emphasize either the lipo10 philie groups or the hydrophilic groups may be used. Commercially available soya lecithin has been used with good results. It is commercially available as a liquid material with lecithin dispersed in a soybean oil carrier. Assuming that the liquid lecithin product contains about 60% lecithin, to obtain a final product containing from say 0.17 to 0-6% lecithin, from 0.25 to 1% of such a lecithin product can be employed.

The use of steam in conjunction with atomizing the mixture supplied to the agglomerating chamber is desir20 able in that it provides an elevated temperature which facilitates formation of aggregates, and in addition, it aids effective atomization with uniform distribution of the atomized material upon the powder particles and provides some of the moisture. Also when lecithin is introduced with the steam it is effectively dispersed and caused to be incorporated with the aggregates as a separate material. In general, it is satisfactory to supply culinary steam at a suitable pressure (e.g., 120 psig).

At the lower fat levels (e.g., 10% or less) it is desirable to supply anhydrous nonfat milk powder to the agglomerating step 12. Thus all of the fat of the final 2727 - 11 product is supplied to the agglomerating step 12 byway of the homogenized mixture from step 11. This simplifies commercial processing because nonfat spray dried milk is not subject to flavor or quality deterioration when stored and shipped in sealed containers without the use of nitrogen or other inert gas. For the higher fat levels in the final produce (e.g., 10 to 28%) it is desirable to make use of some anhydrous fat containing milk produced by spray drying, thereby reducing the amount of fat which is added in the agglomerating operation 12 to attain the desired fat level in the final product. By way of example, assuming that a final fat level of 28% is desired, the spray dried milk supplied to the agglomerating step 12 may have a fat content of 25% and the amount of fat added by way of the homogenized mixture from step 11 may serve to raise the fat content of the final product to the desired 28% level.

Instead of making use of a spray dried milk powder having a fat content which is somewhat less than that desired in the final product, a desirable procedure is to utilize spray dried whole milk (28% fat) and blend the same with nonfat spray dried milk, whereby a blend is supplied to the agglomerating step 12. The blended material has a fat content somewhat less than desired in the final product. The amount of homogenized mixture from step 11 added in the agglomerating step 12 is sufficient to raise the fat to the desired level in the final product. Spray dried whole milk is generally more commercially available than a spray dried milk of lower fat content, and in addition, the use of such a blend facilitates agglomeration at higher fat levels in 43727 - 12 the finished product.

Irrespective of whether or not the dry milk powder has a substantial fat content, is a blend of fat-contain ing milk with nonfat spray dried milk, or nonfat spray dried milk, it is desirable for it to have a relatively low solubility index, as for example, an index of the order of 0.1 or less. A low solubility index indicates a minimum amount of denaturation of the heat coagulable protein of the milk. When the protein is denatured to a substantial extent, it tends to settle out in the reconstituted milk, thus impairing its quality as a beverage. It should be understood, however, that the process of the present invention can be used with milk having a solubility index in excess of 0.1. Processing according to the present invention does not appreciably increase the solubility index of the original powder.

A typical sieve analysis of a product made according to the present invention, with a fat content of 5% (dry solids basis) is as follows: Mesh Screen (U.S. Standard) Percent On 80 54,5 On 100 25,0 Through 100 20.5 25 The pour bulk density of a typical product made in accordance with the process described above is of the order of 0.20 to 0.30 grams per milliliter. A pour bulk density of 0.27 is typical of a product having the above sieve analysis and having a fat content of 5% (dry solids basis). The product produced as described above has good wettability and can be readily dispersed in cold water (e.g., 68°P.) by simple stirring to form a - 13 stable reconstituted milk. Thus, when a quantity is introduced into cold water to form a reconstituted milk, simple stirring with a spoon lor a period of the order of lo to 50 seconds suffices to completely disperse the material. Assuming the source milk powder has a protein content that is not seriously denatured by heat treatment, the reconstituted milk is stable in that no substantial settlement of solids occurs when the milk is permitted to stand for extended periods of the order of 24 hours or more.

A characteristic of products made according to the foregoing process is that when reconstituted with cold water and permitted to stand for periods of the order of 24 hours or more, there is minimal or no noticeable separation of fat or cream at the surface of the liquid. This is true for products having a relatively low fat level, as for example, 5%, and also products having a relatively high fat level of the order of 28%. We attribute this to certain features of the process, including the presence of the emulsifier at the time the cream is homogenized in step 11. As previously explained, this serves to permit homogenization at relatively high pressures with production of relatively small fat globules without phase reversal. Absence of fat separation is attributed not only to the presence of the emulsifier at the time the mix is homogenized, but also to the presence of added nonfat milk solids. Good wettability and dispersibility of the product is attributed not only to the physical character of the aggregates, but in addition, to the fact that the lecithin remains separate from the fat, and therefore is present in such form as to be most -Ineffective as a wetting agent. As previously mentioned, when lecithin is added before the homogenizing step 11, nonfat milk components present, including nonfat milk solids added in step 10, tend to enrobe the lecithin, thereby blocking its wetting abilities in the final product. This enrobing or blocking effect does not take place when the lecithin is introduced into the agglomerating chamber together with the steam.

The apparatus for carrying out the process shown IO in Figure 3 consists of a cyclone feed chamber 25 together with a treatment or agglomerating chamber 26. The cyclone chamber corresponds generally to that of a conventional pneumatic cyclone, and is shown consisting of the upper cylindrical portion 25a and the lower conical shaped portion 25b. A feed supply conduit 27 connects tangentially with the upper portion of the chamber, and an exhaust conduit 28 communicates with the central region of the cyclone chamber and serves to remove air from which powder has been centrifugally separated.

The treatment chamber 26 is shown provided with an upper cylindrical shaped portion 26a together with a lower conical shaped portion 26b. The chamber 26 is in direct communication with the lower end of the cyclone through the coupling conduit 33. It will be noted that the cyclone and the treatment chamber 26 are in axial alignment.

The means employed for introducing a fluid mixture in atomized form may be as illustrated in Figure 4. It consists of a spray nozzle 35 attached to the lower end of the supply pipe 36. The portion of the pipe 36 extending immediately above the nozzle is enclosed within - 15 the jacket 37. One portion of this jacket is connected by pipe 38 with a source of cool air under pressure and the lower end of the jacket is provided with openings from which air is discharged into a region generally surrounding the nozzle 35.

During operation of the apparatus, jacket 37 serves the purpose of preventing contact between the powder being treated and the pipe 36 which, under certain operating conditions, might cause accumulation of solid material. Also the downwardly directed air jets discharging from apertures 39 into the region surrounding the nozzle 35 tend to prevent back swirl and accumulation of solid material on the nozzle.

The nozzle 35 shown in Figure 4 consists of a body which is attached to the pipe 36. It has an orifice and a divergent passage 42 extending from the orifice. A nozzle of this type serves to direct a divergent conical shaped spray into the treatment chamber. The nozzle 35 is within the upper portion of the treatment chamber, and it is generally aligned with the central vertical axis of the chamber.

Conventional means can be used for supplying dry milk powder together with an airstream to the conduit 27 {Figure 3). As illustrated schematically in Figure 3, the conduit 27 may connect to the discharge side of blower 46. A powder hopper 47 communicates with the inlet conduit 48. A powder feed means 49, such as one of the feedscrew type, serves to deliver powder at the desired regulated rate to the hopper 47.

The treated material in the form of moist porous aggregates drops by gravity through the lower end 51 of - 16 the treatment chamber 26. As shown in Figure 3, the discharge opening 51 is shown delivering the moist material directly to the dryer 52. This dryer can be of the shaker type consisting of a main body 53 which has an inlet end 56 coupled directly to the lower end of the treatment chamber. Warm dry air is introduced below the screen through conduit 57. Air is removed from the space over the screen by the hood 58 and conduit 59. The flexible cloth walls 60 couple the lower end of the hood to the upper side of the body 53. It will be understood that two or more stages of such drying units can be used as desired.

The upper part of chamber 26 is shown connected by chamber 61 and conduit 62 with a suction fan 63.

This conduit also connects with the exhaust conduit 28.

By adjusting the damper 62a, a controlled amount of cool atmospheric air may be drawn into the lower opening 51, thus causing the downwardly falling aggregates to be enveloped in upwardly moving temperate air.

The walls of chamber 26 can be kept at a temperature corresponding generally to the mean temperature of the atmosphere within the same. Thus, these walls may be covered by heat insulating material, or they may be provided with a jacket 64 connected with the hot air supply conduit 65a and the discharge conduit 65b.

With this arrangement, warm air can be circulated through the jacket to maintain the walls of the chamber 26 at a desired temperature level.

Figure 4 shows means for supplying the nozzle 35 with lecithin which is to be atomized and dispersed in the agglomerating chamber. It consists of a mixing 42737 - 17 device 66 having a tapered discharge end connected to line 36. The hollow body has an inner tube 67 which connects with the incoming line 68. Also the body has a side inlet which connects with the incoming line 69. Swirl fins or vanes 70 are shown within the tapered portion of the body. Line 68 connects with suitable means, such as a metering pump, which is capable of supplying the lecithin product at a predetermined controlled rate. Line 69 connects with a source of steam as illustrated, and a mixer 71 connected with a source of water as indicated by line 72 may be connected in this line.

As illustrated in Figure 4, an additional nozzle 74 is provided alongside the nozzle 35. This may be a high pressure atomizing nozzle such as is commonly used in milk spray drying equipment. Pipe 75 connects with nozzle 74 and is supplied with the homogenized mix from the homogenizing step 11. A suitable high pressure pump supplies the material to pipe 75 at a relatively high pressure of from 1500 to 4000 psig. Atomizing nozzle 74 produces a divergent spray through which the downwardly moving powder passes, with the spray being commingled with lecithin and water vapor being sprayed downwardly by the nozzle 35. Thus the powder particles commingle with the homogenized fat-containing mixture produced in atomized form by the nozzle 35, while at the same time the powder particles are commingled with droplets of lecithin dispersed by the steam, and the steam and moisture present in the fat emulsion create a humid atmosphere within the agglomerating chamber.

Operation of the arrangement shown in Figure 4 is as follows. Steam at constant pressure (e.g., 120 2727 - 18 psig) is supplied to the line 69, and the lecithin product in liquid form, is supplied through line 68 at a predetermined constant rate. The steam supplied by way of line 69 is caused to be intermixed with the lecithin by virtue of the swirling action induced by the vanes 70. As a result, a relatively homogeneous mixture of lecithin and steam is delivered through line 36 to nozzle . Some water can be introduced together with the steam by controlled admission through line 72, depending upon the moisture and temperature requirements within the agglomerating chamber.

Figure 2 illustrates another embodiment of the process in which the cream mixture is subjected to heat treatment 15 for flavor improvement. Thus as in the process of Figure 1 the emulsifier together with milk solids and cream are supplied to the mixing step 10 where the mixture is heated to 170 to 190°F. (180°F. optimum) and held at this temperature for 5 to 15 minutes (10 minutes optimum). Thereafter the material is cooled to 145 to 150°F. and homogenized in step 11, as in Figure 1. The agglomerating step 12 is carried out in the same manner as in Figure 1, and as indicated, the milk powder being supplied to the agglomerating step is a blend of spray dried fat-containing, powder (e.g., whole milk powder) and nonfat milk powder. The remainder of the process as shown in Figure 2 is the same as in Figure 1. As indicated in Figure 2, a small amount of an antioxidant (e.g., 0.05% fat basis Tenox 7) may be added to the cream together with the emulsifier in mixing step . TENOX is a Trade Mark.

As described above, cream is used as a source of fat. However, in place of using dairy cream it is - 19 possible to use butter oil together with sufficient nonfat dry milk powder and water, whereby the material after being homogenized in step 10 has the desired fat milk solids and water contents comparable to cream for use in the agglomerating step 12. While the products made by use of butter oil are of good quality, it has been our observation that the flavor is slightly different from products made with dairy cream, which is attributed to the relatively strong butter flavor of the butter oil. Also other fats can be used in place of butterfat. Such fats should be edible, relatively free from free fatty acids, and may have melting points of the order of 70 to 12O°F. Butterfat has a melting point of the order of 90°F. For example, reference can be made to any one of a number of edible hydrogenated vegetable oils or fats such as hydrogenated coconut, cottonseed, peanut and corn oils having melting points of from 70 to 120°F. When making use of such vegetable fats, an emulsion or cream is prepared in step 10 by mixing the fat with a suitable amount of water and emulsifier at a temperature above the melting point of the fat. Also some milk solids can be added to the mixture, the same as when using dairy cream.

Examples of the process are as follows:Example 1.

In this example a product was prepared having a fat level of 5%. The procedure was generally as illustrated in Figure 1. The source material was commercial spray dried anhydrous nonfat milk powder having a bulk density of about 612 grams per liter and a total moisture content of about 2%. The solubility index was about 0.1. - 20 This powder was fed pneumatically at a metered rate to an agglomerating chamber as shown in Figure 3. A good quality edible fresh dairy cream analyzing 40% butterfat was adjusted to a fat level of 22.5% fat and 45% total solids by the addition of nonfat dry milk powder reconstituted in water. To this cream there was added 1.5% of emulsifier (on a fat content basis), the emulsifier being a blend consisting of 16.67% monoglycerides and 83.33% ethoxylated mono and diglycerides.

The resulting mixture was heated to 180°F., held at that temperature for 10 minutes and then cooled to 145150°F. The mixture was then passed through a commercial homogenizing equipment, the first stage being at a pressure of 3000 psig, and the second stage at 500 psig.

Homogenization was carried out at a temperature level of 145 to 150°F. The nonfat milk solids were pneumatically conveyed into the agglomerating chamber. The homogenized cream mixture was pumped to the atomizing nozzle 74 at a pressure of 1500 to 2000 psig, the rate being consistent to produce the desired fat level in the final product. A soybean-lecithin product was metered into the steam line 69 at a rate to attain a 0.6% lecithin level in the final product. The amount of steam added was sufficient to control the moisture level of the aggregates leaving the agglomerating chamber at a total moisture level of from lo to 11%.

The moist agglomerated material was then dried to a moisture content below 2%.

The resulting instant fat containing milk product was of excellent quality with a pour density of 0.27 grams per milliliter. When subjected to the wettability test as disclosed in U.S. Patent 3,231,386, the wetta42727 - 21 bility proved to be excellent, the powder sinking in cold water within a period of 15 to 20 seconds. When stirred in cold water the powder gradually dispersed over a stirring period of about 8 seconds to produce a reconstituted milk having its surface free of floating material. When stored in a refrigerator at a temperature of 40°F. for a period of 24 hours, no appreciable separated cream was noted upon the surface of the liquid. Also no appreciable amount of settled undissolved solids was noted. Xn general, the product when reconstituted was of good quality, having a good mouth feel and flavor.

Example 2.

In this example a product was prepared having a fat level of 28%, corresponding to whole milk powder.

The same cream mixture was prepared in the same manner as described in Example 1. However, the source of anhydrous powder comprised 25% of commercial spray dried whole milk powder having a fat level of 28%, blended with sufficient spray dried nonfat milk powder to provide an average fat level of 25%. The remainder of the process was the same as in Example 1. The rate at which the blended powder was supplied to the agglomerating chamber,and the rate of feed of lecithin and homogenized cream mixture to the chamber was such as to provide a final fat level of 28%, with a lecithin content of 0.8%. The final product was readily dispersible in cold water with simple stirring with a spoon. There was minimal cream separation upon the surface of the reconstituted milk, and in general, the reconstituted milk was of good quality with good flavor and mouth feel. - 22 Taking the directions and data of Examples 1 and 2, one can readily determine how to apply the process to the production of instant dry milk having fat levels other than 5 or 28%. For fat content less than 5%, such as 2%, the procedure would be substantially the same as Example 1 and the source material would be nonfat dried milk powder. For a fat level of say 15%, the source material could be anhydrous whole milk powder blended with nonfat powder to provide an average fat level of say 12%. Since the fat emulsion mix would have a fat content to provide 15% in the final product, the amounts of added emulsifier and nonfat milk solids added to the mix would be adjusted accordingly.

In the foregoing references to the use of fat containing spray dried milk, and particularly to whole milk, care should be taken to select a whole milk of low heat type having its heat denaturable protein substantially undenatured and having a low solubility index (e.g., 0.1 or less). Also when reconstituted with water it should have good flavor characteristics and should not be subject to objectionable fat separation. Such spray dried whole milk is available commercially and is made by low heat processing before spray drying.

For special markets where a certain amount of cooked or heated flavor is desired, medium heat powder may be used. While commercial spray dried whole milk has been used with satisfactory results, it may be desirable to produce such milk by special processing to avoid conceivable fat separation in the reconstituted milk. Thus small amounts of emulsifier as previously described would be added to the fluid milk, and the milk homogenized at high pressures (e.g., 3000 to 3500 psig - 23 second stage)before spray drying. The amount of emulsifier used should be at a low level to avoid flavor impairment. With such special processing the fat globules are reduced to small size (e.g., less than 3 microns) without release of free-fat or fat churning.

In the foregoing examples, crude lecithin is employed in liquid form, when economically available we prefer to employ a purified form of lecithin which may be in the form of a powder. The powder can be dispersed in a suitable liquid medium, such as butter oil, and introduced with steam as indicated in Figures 1 and 2. A particular commercial purified lecithin is marketed by Lucas Meyer, Hamburg, West Germany, under the trade name Metarin. The use of such purified lecithin is desirable because it avoids possible flavor impairment of the final product, such as may be caused by undesirable flavor components of crude lecithin.

Xt has been found that the process described above produces instant fat-containing milk of acceptable quality which can be readily reconstituted with warm or cold water to form a stable reconstituted milk, is not subject to objectionable fat separation for a wide range of fat contents, and which has good flavor characteristics.

Claims (23)

1. A process for the manufacture of instant fatcontaining dry milk making use of an agglomerating chamber, which process comprises the steps of supplying 5 anhydrous dry milk powder to the chamber and causing the powder to be dispersed therein, further supplying to the chamber atomized material consisting essentially of lecithin and a fat-water emulsion, the lecithin being separately supplied to the chamber in atomized form, 10 the further supplying resulting in the atomized material being commingled with the dispersed powder particles within the chamber whereby powder particles are caused to adhere together in the form of porous random aggregates with the fat and lecithin simultaneously being dis15 tributed on the particles and the aggregates, and then removing excess moisture from the aggregates to form a dry product.

2. A process as claimed in claim 1 in which the amount of lecithin supplied is such as to provide a 20 lecithin content of from 0.17 to 0.6% by wt. in the final product.

3. A process as claimed in claim 1 or claim 2 in which the fat-water emulsion is prepared by adding an emulsifier to the same and by subjecting the mixture 25 to high pressure homogenisation whereby the bulk of the fat globules in the emulsified material have a size of less than 3 microns.

4. A process as claimed in claim 3 in which the emulsifier is selected from mono and diglycerides of 30 long chain fatty acids and combinations thereof.

5. A process as claimed in any one of claims 1 - 25 to 4 in which the fat content of the emulsion has a melting point of from 70 to 120°F.

6. A process as claimed in claim 4 in which the emulsifier cons’ists of a blend of said emulsifiers.

7. A process as claimed in any one of claims 1 to 6 in which the fat-water mixture before being homogenized is held at a temperature of from 170 to l90°F. for a period of 5 to 15 minutes for flavor improvement.

8. A process as claimed in any one of claims 1 to 7 in which the milk powder supplied to the agglomerating chamber consists of a blend of anhydrous fat-containing milk powder and an anhydrous nonfat milk powder.

9. A process as claimed in claim 3 in which nonfat milk solids are added to the fat-water mixture before homogenizing the same.

10. A process for the manufacture of instant fatcontaining dry milk making use of an agglomerating chamber, which process comprises the steps of supplying anhydrous dry milk powder to the chamber and causing the powder to be dispersed therein, further supplying atomized material to the chamber, the further material consisting essentially of lecithin and a fat-water emulsion, the lecithin being introduced separately into the agglomerating chamber together with steam, the fatwater emulsion being prepared by mixing materials including fat, water, an emulsifier and nonfat milk solids and by then subjecting the mixture to homogenization at a pressure of at least 2500 psig or higher, whereby the bulk of the fat globules present in the homogenized material has a si2e of less than 3 microns, and whereby - 26 the material has a minimum of free fat, the further introduction of the atomized material being such that the material is 'commingled with the dispersed powder particles within the agglomerating chamber whereby the 5 powder particles are caused to adhere together in the form of porous random aggregates with the fat and lecithin simultaneously being distributed on the particles and the aggregates to form a dry product.

11. A process for the manufacture of instant fat1O containing dry milk making use of an agglomerating chamber comprising the steps of supplying nonfat anhydrous dry milk powder to the chamber and causing the powder to be dispersed therein, further supplying an atomized material to the chamber where said atomized material consists 15 essentially of lecithin and a fat-water emulsion, the lecithin being separately supplied to the chamber in atomized form, the fat content having a melting point of from 70° to 120°F. and such that the further supplying results in the atomized material being commingled with 20 the dispersed powder particles within the chamber whereby the milk powder particles are caused to become sticky and to adhere together in the form of porous random aggregates with the fat and lecithin simultaneously being uniformly distributed on the particles and the 25 aggregates, and then removing excess moisture from the aggregates to form a dry product.

12. A process for the manufacture of instant fatcontaining dry milk making use of an agglomerating chamber, which process comprises the steps Of supplying 30 nonfat anhydrous dry milk powder to the chamber and causing the powder to be dispersed therein, further 43737 - 27 supplying atomized material to the chamber wherein the atomized material consists essentially of lecithin and dairy cream, the lecithin being separately supplied to the chamber in atomized form, the cream being prepared by homogenizing the same in the absence of lecithin, and such that the further supplying results ih the atomized material being commingled with the dispersed powder particles whereby the powder particles are caused to become sticky and to adhere together in the form of porous random aggregates with the fat content of the cream and the lecithin simultaneously being uniformly distributed on the particles and the aggregates, and then removing excess moisture from the aggregates to form a dry product.

13. A process as claimed in claim 12 in which the cream before being homogenized is treated by heating the same to a temperature of from 170 to 190°P. and held at such temperature for a period of from 5 to 15 minutes to improve the flavor of the same.

14. A process as claimed in claim 12 or claim 13 in which an emulsifier is added to the cream before the cream is homogenized.

15. A process as claimed in claim 12 or claim 13 in which both milk solids and an emulsifier are added to the cream before being homogenized.

16. A dry milk product whenever prepared by a process as claimed in any one of claims 1 to 9.

17. A dry milk product whenever prepared by a process as claimed in claim 10.

18. A dry milk product whenever prepared by a process as claimed in claim 11. - 28

19. A dry milk product whenever prepared by ει process as claimed in any one of claims 12 to 15.

20. A process for the manufacture of a dry milk product substantially as hereinbefore described with 5 reference to Figure 1 or Figure 2 of the accompanying drawings.

21. A process for the manufacture of a dry milk product substantially as hereinbefore described with reference to Figures 3 and 4 of the accompanying drawings. 10

22. A process as claimed in claim 1 substantially as hereinbefore described in Example 1 or Example 2.

23. A dry milk product whenever prepared by a process as claimed in any one of claims 20 to 22.