CA1113300A - Instant yogurt and process for its manufacture - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Processes are provided for preparing powders which can be instantly reconstituted to a true natural yogurt. The process includes the following three steps, namely: (1) innoculating a liquid milk product with sufficient bacterial mixture of Lactobacillus bulgaricus and Streptococcus thermophilus in a ratio of between 0.5:1 and 1.5:1, e.g. 1:1 and optionally also containing a minor amount of Lactobacillus acidophilus and incubating the innoculum at a controlled temperature of 41 - 46°C. for a sufficient amount of time to provide a solution having a pH of 4.3 - 4.4 and further optionally in a two stage/two temperature incubating procedure; (2) subjecting the yogurt so prepared to sub-zero temperatures until the yogurt is frozen to a temperature below its eutectic point, and (3) removing substantially all the water from the frozen yogurt by subjecting the frozen yogurt in a closed environment to a very low absolute pressure and a controlled heat input within a temperature range of -40°C. to +40°C. and having a condensing surface therein maintained at a temperature below -40°C. to -80°C., thereby to convert the yogurt to particulate form, to provide a shelf stable powdered yogurt. Such yogurt powders, having low sugar and low sodium, are also provided by subjecting the liquid milk product, e.g., a skim milk or a skim milk/whey preparation to ultra filtration or by passing it through a molecular sieve.

Description

This invention relates to an "instant" yogurt and to the process for its manufacture. The instant yogurt is in ~ dry particulate form which can be reconstituted by admixture with water to provide a product of true, natural yogurt texture and flavour.
Yogurt is coagulated milk product obtained by lactic acid fermenta-tion through the action of Lactobacillus bulgaricus and Streptococcus thermo-ph lus from milk, milk solids and other m:Llk products. The microorganisms in the final product must be viable and abundant. Fresh yogurt is a living pro-duct subjec~ to changes of continuous fermentation. Thus, it is non-uniform and perishable. It would therefore be desirable to provide a rnodified yogurt which can be stored indefinitely and which can be reconstituted simply by ad-ding water and stirring, thereby to provide a product having a texture and taste identical to true natural yogurt~
One proposal to provide instant yogurt was made by E.A. Ferguson, Jr.
in United States Patent No. 3,080,236 dated March 5, 1963. This patent de-scribes a process which includes first making natural yogurt by implanting a pure culture in milk. After incubation for 12 hours, the resultant yogurt is reduced in volume by evaporation, then placed in vacuum driers until all moisture is removed9 after which the dried product is pulverized. In produc-ing a powdered yogurt of this type, substantially all the beneficial micro-organisms are destroyed and so the product is not a true, natural yogurt.
~ erguson further teaches that when yogurt in its usual form is dehydrated it cannot be reconstituted into the smooth, creamy, pleasant tasting product by the simple addition of water as might be expected. To overcome this difficulty, Ferguson's process comprises drying the culture of yogurt in a vacuum dryer, and powdering the residue to be used as a partial ingredient of an instant yogurt product~ Preferably the dried, powdered culture residue is prepared from a culture which has been over-grown to some extent. Then, the dried, powdered ~ogurt culture is mixed iitn ~o~dered rnilk~skimmed rnilk, norl-fat milk, or the ~ike), and with ' 3f~1 ~tarch, preferably dried, cooked starch, to form the composltlon of that ln-vention. Flavourings, sweeteners, or the like, may be added as desired. W~len this composition is mixed with water, a yogurt-like composition is in~tantly formed. The resulting yogurt-like product, although it is not true natural yogurt, was alleged to look, taste and act like yogurt in all respects. Fer-guson's yogurt product, comprising dried yogurt culture, a water-soluble dried milk, an edible fat and a water-soluble dried starch was thus adapted when mixed with water to form a synthetic yogurt composition. Ferguson's lnstant yogurt, therefore, is lacking in the full benefits of good quality true natur-al yogurt.
Another proposal was made by Hockenberg et al. in United StatesPatent No. 3,321,319 patented May 23, 1967. While Hockenberg et al. suggested that it was known to subject milk and dairy products, Eor example, yogurt, to freeze-drying in a "conventional" manner, whereby the crude product, after the freezing step, was dried by sublimation of the ice under vacuum, and thereby a satisfactory dried product was obtained, they also taught that such proced-ure was not industrially viable because of economic considerations. Conse-quently, as an improvement on this old teachings, they provided a free~e-dried liquid dairy product by a procedure where a dairy product, e.g. milk, was separated into a serum or skim portion and a coagulated residue by mechani-cal means. Then the coagulated residue, preferably immediately following its separation, was subjected to cooling and then was subjected to a free-drying step in accordance with conventional methods. The serum constituent was dried in its separated state, employing known drying methods. ThereaEter, the pro-ducts of both drying steps were mixed together to form the final dried pro-duct.
Hockenberg et al taught that by the mechanical separation of the aqueous serum portion and the coagulated residue, those salts and sugar con-stituents which would have an adverse effect lf the entire mass had been pre-concentrated in a single step, remained in an aq~!eous serum portion, and 3~

thereby the coagulate provided an especially suitable starting material for subsequent freeze-drying. It was taught that separation of the serum portion and the residue could be carried out mechanically in a variety of ways, either by centrifuging, sieving, or settling of the solution. While the patentees taught that their process would be applicable to yogurt, it was, in fact, not so, i.e., they taught a process for the preparation of a yogurt-curd powder, comprising the steps of: (a) treating yogurt ~ilk with an enzyme to form a coagulated protein residue and a serum portion; (b) separating the protein re-sidue from the serum; (c) cooling and freeze-drying the protein residue; (d) drying the serum portion; and (e) admixing the dried serum and protein residue to form a dry yogurt product~ The drying process would kill many of the yo-gurt-producing bacteri~, and thus the reconstituted product would then not be a true natura~ yogurt.
Yet another proposal was made by Bohren, in United States Patent No.
3,793,465 patented February 19, 1974 which taught a method for the Manufacture of an acidified milk product in powder form in which a fraction of a milk pro-duct inj-powder form, biologically acidified to a pH of 4.2 to 4.4, was comr bined with another fraction of a non-acidified milk product in powder form in order to obtain a pH above 5.2. Immediately after reconstitution with water, the weight of the water was 5 to 10 times the weight of the powder, and an acid compound with controlled release was combined with the two fractions of milk product. Nevertheless, the method included the step of drying the milk product to form powders by conventional methods, e.g., by injection into a drying chamber at a temperature of 60 - 100C. through spray nozzles. Such spray-dried product could not contain any live yogurt bacteria, and so when recon-stituted car.not be considered as being true, natural yogurt. Moreover, the spray-dried powders were mixed with an edible acid in particulate form, the edible acid being citric acid, lactic acid or acid Lruit concentrate. Each particle had a coating of edible fat having a melting point bet~een 45 and , 3~

60~C., and an edible emulsifier thereon. The edible acid constituted from 50 to 80% of the weight of the particles. The particles after coating were be-tween 50 and 250 micrometers in size. The quantity of edible acid was such that, after 2 hours subsequent to reconstitution, the product had a pH of 4.3. The edible fat coating had a composition and thickness such that all acid coated therewith was released in rom l/2 to 2 hours after reconstitution.
Such reconstituted product cannot be considered as being true, natural yogurt.
Yet another proposal which had been made was in the Barberan United States Patent No. 3,985,901 patented October 12, 1976. That patentee deseribed ¦
lQ a complex process for producing and preserving acidophil milk which was mainly based on the combination and harmoni~ation of cultivating and drying processes (which was alleged to be generally applicable to other fermented milks, and yogurt). Such process was alleged to permit: obtention of abundant lacto-bacillus cultures; grading the contents of the live lactobacillus in the pro-duct by the weighted addition of excipients corresponding therewith; a prac- !
tically unlimited preservation without the need of refrigeraticn, since the product would be in a dry powdered rform; an easy and rapid recons~itution, ready to be consumed, by means of simply restoring the original water; im proving the organoleptic qualities by the incorporation of harmless hydrophil substances which provided a creamy consistency, or fruit essences and sweeten-ing substances to satisfy the taste of certain consumers or to lessen unde-sirable flavours or colours; possibility of being consumed by certain persons (diabetics, pre-diabetics, etc.) due to the incorporation of suitable natural or synthetic sweetening agents, instead of the conventional sugars; possi bility of approaching the organoleptic qualities of yogurt, due to the rational mixture of the dry mass thereof with the dry mass of yogurt in suitable proportions so that the predominating character of the acidophil milk was not lessened; and relatively economical production and commerciali-~ation costs since inexpensive processes of careful spray-drying (whereby the main ~ass of the nutritious medium of the fermented mil~ is obtained in a dry 3g~

form) are combined with other more expensive lyophilization processes having a small but rich mass of microorganlsms (whereby the appropriate and standar-dized quantity of live and dry lactobacillus is contributed to the main spraye~ :
mass). Such patented process for drying and preserving acidophil fermented milk in powdered form so that it could be readily reconstituted with water comprised the following twelve steps 7 i. e .

1. culturing a lactic acid producing microorganis~ in a cultu~e medium to produce an inoculum;

2. sterilizing milk to be fermented, and adjusting the solids content of such milk to approximately 16 to 20% solids content;

3. fermenting the milk of step (2~ with the inoculum of step ~;
(1~ in a continuous or discontinuous manner;

4. inoculating a culture medium with the inoculum of step (1) and fermenting ~mder conditions sufficient to obtain a large proliÇeration of the lactic acid-producing microorganism;

5. enrishing the solids content of the fermented milk of step ~3) with - a. 15 to 20% sugars or other sweeting -agents and b. 1 to 2~ thickening agents;

6. homogenizing the sweetened, fermented milk of step (5) by mechanical means to destroy any gelled particles and to improve fluidity;

7. spray drying the product of step (6) at from 130 to 180C., where the survival of lactic acid-producing microorganisms is desired, or at 180 to 300C. where such survival is not necessary but increased yields are desired;

8. agglomerating the product of step (7~ in a moist atmosphere and then drying it in a fluidized bed;

:. ;. .. . : ,:; : ,

9. lyophili~.ing the lactic acid-producing microorganisms from the fermentatlon of step (4) by rapid freezing under condi~ions to pro-mote the survival of the microorganisms and thereby produce a foamy freeze-dried mass co~prising live lactic acid-producing microorganisms;

10. grinding the foamy mass resulting from the lyophilization of step (9) to a granulometry similar to that of the product of step (8);
ll. mixing the lyophilized product of step (10) with an excipient so as to achieve a lactic.~acid-producing microorganisms content in the lyophi-li~ed product of 10l microorganisms per gram 12. mixing the lyophilized product of step (ll) with the product of step (8) in a proportion ofapproximately 40 parts by weight of the product of step (8) and 2 parts by weight of the product of step (11? so that when reconstituted with water in an amount of 42 grams of fermented dry milk per 100 to 125 cc of water, there is obtained a creamy, liquid, fermented acidophil milk having about 200 million lactic acid producing microorganisms per cc. Clearly this complex process does not solve the problem of readily, easily and economically providing a dried powder which can be instantly be recDnstitoted into a true natural yogurt.
- Finally, Schur? in Unit~d States Patent No. 4,066~794 patented Janua~y 3, 1~78 provided an instant yogurt p~epa~ation adapted, when ~ixed with water to form a composition whose smooth texture and nutritional value was comparable to that of natural yogurt. The preparation consisted essenti-ally of dried yogurt powder in which the culture was deactivated, a dormant dried yogurt culture, water-soluble dried milk powder, sodium alginate in an amount of 5.20 percent by weight to act as a setting agent to form a viscous colloidal solution in which the milk and yogurt constituents are dispersed, an organic dispersing agent to promote the uniform separation of the fine particles of the solution, the organic dispersing agent being sugar in an amount 69.26~ by weight, and a sequestrant constituted by F~TA in sufficient . .

~33~

quantity to inhibit Rrecipitation reactions that would otherwise cause the sodium alginate settin~ agent to curdle and create lumps in the composition.
This also is not a true yogurt since the yogurt powder used is in the deacti-vated state because of the processing of natural yogurt with heat to remove all moisture therefrom which acts to destroy the culture.
Accordingly, the art i5 still faced with the solution of the problem of providing an "instant" yogurt powder. Accordingly, an object of a broad aspect of this invention is the provision of a simple process for readily,easily and economically providing a dried powder which can instantly be re-constituted with water to form a true natural yogurt.
By one broad aspect of this invention, a process is provided `~
for preparing a powder which can be instantly reconstituted to a true yogurt, the process comprising: (1) innoculating a liquid milk product with sufficient bacterial mixture of Lactobacillus bulgaricus and Streptococcus thermophilus in a ratio of 0.5:1 to 1.5:1 and incubating said innoculum at a temperature of 41 -46C. for a suf~icient amount of time to provide a solution having pH of 4.3 -4.4; (2) subjecting the yogurt so prepared to sub-zero temperatures until said yogurt is frozen to a temperature below its eutectic point; and ~3) removing substantially all the water from sald frozen yogurt in a closed environment sub-jected to low absolute pressure and a heat input withln a controlled temperaturerange of -40C. to ~40C. and having a condensing surface therein maintained at ; a temperature below -40C. to -80C., and converting said ~reeze-dried yogurt to particulate form, thereby to provide a shelf-stable powdered yogurt.
By one variant, the liquid milk product is skim milk.
By another variant, th~ liquid milk product is reconstituted skim milk provided by dissolving skim milk powder in water.
By another aspect, the innoculating step includes incubating the innoculum with said Iactobacillus bulgaricus and Streptococcus the _ philus at a ratio of 1:1 for a period of 4 - 6 hours at a temperature of 41 - 46C., 30 -- and then incubating said partially incubated innoculum at a temperature of 36 -- : - , :: ~, ' :,,, - .:.' ,., . .::': :: . : :,, i ~ ~33~

38C. for a further period of 2 - 4 hours, thereby to provide variations in tex~ure, taste and aroma in the yogurt ~o-produced.
By a further aspect, the innoculating step includes innoculating with an amount of a bacterial mixture amounting to 2% o~ the volume of the liquid milk product of Lactobacillus bulgaricus and Streptococcus thermophilus in a ratio of 1:1, and including ~rom 0.5-1.5% of Lactobacillus acidophilus, thereby to provide variations in flavour in the yogurt so~produced.
By a variation thereof, the reconstituted skim milk solution is heated to 85 - 95%C. for 10 - 20 minutes and is then cooled to 41 - 46C.
prior to being innoculated.
By another variation, up ~o one-third of the skim milk powder is replaced with whey powder.
By still another variation, the process includes the step of subjecting the liquid skim milk product to ultrafiltration prior to being innoculated, the~eby substantially to eliminate molecules having a molecular weight less than 10,000.
By yet another variation, the process includes the step of passing the liquid milk product through a molecular sieve prior ~o being innoculated, thereby substantially to eliminate molecules having a molecular weight less than 10,000.
By another variant, the process includes the step of adding fruit or other flavourings, e.g., strawberry, red raspberry, blueberry, cherry~
peach, apple, blackberry, pineapple, etc. to the yogurt prior to being subjected to steps (2) and (3).
By another aspect, the dry yogurt powder has the following composition:

% by weight Protein 23 - 36 Carbohydra~e 5 - 34 ~
Fat ~0.8 - 3.5 :
Moisture 3 ~ 5 Ash 8 - 9 ~;
Other balance By another aspect1 the reconstituted yogurt has the following comr position:

% by weig_t Protein 8.2 Carbohydrate1.5 - 4.5 Fat 0.9 - 1.0 Ash 1.5 - 2.5 Other balance Calories 30 - 75 By a further aspect, the dry yogurt powder has th~ following comr position Protein 26 - 36 ~ :
Carbohydrate5 - 34 Fat 0.8 - 3.5 Moisture 3 - 5 Ash 8 - 9 Other balance and also containing freeze-dried fruit therein.

_ 9 _ - - :: - - . : -: : :: .- :: : :~ : : - :. .: : .

' .' ~ . ' ' ' . . ',, . . , , . , ! . .

33~
` The intrinsic ~niq~le novelty behind the principles of the present invention which provide an unobvious improvement over the generalized teachings of the Mockenberg et al U.S. Patent referred to above resides not only in the production of the crude product (the yogurt) but also in the particularization of the freezing and drying steps. It is known that the optimum temperature and pll for the ~rowth of ~ ptococcus_thermophilus is 37.7C. and 6.8 respectively, and for Lactobacillus bulgaricus is 43.3C. and 6.0 respectively. Neverthless, by aspects of the present invention, the production o~ the yogurt is carried out by incubating the microorganisms at a controlled temperature of ~ 46C. until the yogurt has a pH 4.3 - 4.4.
This provides a yogurt product which is especially adapted for the freezing and drying steps within_the ambit of aspects of this invention. This particular procedure is not disclosed nor suggested by Hockenberg et al. In addition, the variant whereby the incubation takes place at two contro]led temperatures, i.e.
a first higher temperature of 41 - 46C. and then a second lower temperature of 36C - 38C. provides a yogurt product which is even more specially adapted Eor the freezing and drying steps.
The yogurt is solidly frozen before being subjected to very low absolute pressure (high vacuum) and a controlled heat input by a pL-ocedure which differs significantly from Hockenberg et al's freeze dryin~ in the conventional manner.
The yogurt must be solidly frozen below its eutectic point, e.g., to a temperature to -60C. to -90 C. The so-frozen yogurt is dried in a closed environment by sublimation by providing a condensing surface having a temperature of -40C. to -80C. or less and an absolute pressure of between 5 and 250 microns, preferably to 25 microns of Mg and subjecting the closed environment to a source of heat input controlled between -40C. and ~65C., to drive the water from the solid to the vapor state by sublimation.

h~ - 9a -33~!~
~ The basic reason for pre-Ereezing the yogurt is to lock its solid particles firmly into position, so that moisture can be sublimed, and physical and chemical reactions cannot take place, and so that the microorganisms are maintained dormant. To assure that the yogurt is frozen to below its lowest eutectic point, the freezer is maintained at a temperature of -60C. to -90C. If the lowest eutectic point is not achleved, the yogurt may appear to be fro~en, when in fact a small percentage may yet be in the liquid state. This small volume of liquid will case the solids in suspension to react, spoillng the results of the dehydration. On the other hand, freezing the product too far below its lowest eutectic is unnecessary and poor practice economically. Optimum rates of sublimation are obtained by the maintenance o an optimum vapor pressure differential between product ice and condenser ice. In practice, the yogurt is generally frozen to a temperature of not lower than -60 C. to -80 C.
The removal of the water is achieved in a closed zone provided with a condensing surface. It is important that the condensing surface be placed in the direct path of migrating vapors. As vapor molecules leave the product ice, they migrate toward the low pressure areas in the system, first, the area just above the product ice, then~to the localized low pressure area surrounding the condenser. On contacting the condensing surface, migrating vapors give up their heat energy, turn to ice, and are effectively removed from the system. Air and other non-condensable molecules emitted from the product pass the condensing surface and are evacuated by the vacuum pump.
According to aspects of this invention, the yogurt can be dried efficiently with a condensing surface temperature between -40C. and -80Co The removal of the water is further achieved in the closed zone which is subjected to a very low absolute pressure. The purpose of the vacuum system is to evacuate non-condensable gases from the chamber, c}eating the vacuum necessary for efficient sublimation. This effectively reduces the resistance to the flow of water vapors migrating from product to the condenser.

~ - 9b -~ ~ ,, , ;, , ,: - . ~ :

3~3 The absence of air in the system also substantially prevents oxidation during drying. The pressure should be 250 microns, preferably 25 microns or less. Ultimate vacuum should be as low as 5 microns.
The r~moval of the water is still further achieved in the closed zone which is subjected to controlled heat. Heat is applied to the ice within the yogurt to maintain the migration of water vapors fronl the yogurt toward the condensing surface. The application of heat to the yogurt supplies the necessary energy to drive off these vapors, raising the temperature of the yogurt (an amount corresponding to the increase in vapor pressure at the ice interface). In the beginning of the cycle, the total volume of the yogurt is frozen and will accept a high heat setting Later when a portion of the product is dry and offering resistance to the vapors released from below, a lower heat setting is desirable to avoid "melt back", i.e. change , in the yogurt from solid to liquid. In the inal portion of the drying cycle, a higher setting may again be desired to drive off any remaining bound molecules. Therefore, it is necessary that heat supplied to the product be controlled. According to the process of an aspect of this invention, the range of control should be between ~40C. and 40C. By these means the temperature of the yogurt during the freeze-drying process is controlled so as to avoid the aforesaid "melt back". The product temperature was maintained within the range of -40C. o -60C. at the commencement of the drying and at +30C. + 5~C. during the later stages of the drying.

,:

: ::, : :, , :. ~ ~ .: : ;` : .: . .' :, 3~

The following are examples of aspects of this inven~ion.
Example I - Plain Skim Milk Instant-Yogurt To 1000 grams of skim milk powder, 2600 gm of water is added.
The mixture is stirred until all the powder is in solution. The skim milk powder had the Eollowing characteristics:
Typical Chemical Analysis Carb~hydrates (Lactose) 52,3%
Proteins 35 5%
Minerals 8.0%
Moisture 3,0%
Fat 0.8%
' ,: ;~:

' - 9d -Physical Charac~eristics Colour - white to light creamy Flavour and odour - sweet and clean Free from hard lumps ~icrobiological Analysis Standard Plate Count less than 50,000/gm Coliform less than 50/gm E. Coli negative Salmonella negative The solution is heated to 90C. and kept at that temperature for 15 minutes. The solution is then cooled to 43C. and a bacterial mixture of Lactobacillus bul aricus and Streptococcus thermophilus in a ratio of 1:1 is g . .
added to the solution. If desired, 0.5 - 1% of Lactobacillus acidophilus may also be added as part of the bacterial mixture. The bacterial may be obtained from the American Type Culture Collection at Bethesda, Maryland. The amount of bacterial added is dependent on the volume of the solution but is usually at 2~ of the total volume of the milk solution.
The solution with the bacteria is incubated for 6 hours between 41 ~

46C. until the pH is 4.3 - 4.4. If desired, the incubation may be done in two steps, i.e. one step for 4 - 6 hours at 41 - 46C. and the second step for 2 - 4 hours at 36 - 38C. until the pH is 4.3 - 4.4. At that pH, the milk solution exists as a firm gelled yogurt. Fruit or other dehydratable flavour-ing agent may also be added to the yogurt gel so formed.
This gel is spread on a tray sepcially designed to fit into a freeze-dryer. The spread yogurt is placed in a freezer at -60C. and kept there un-til the yogurt is frozen.
The frozen yogurt is then placed into a precooled freeze-dryer equipped with a cooler-heater so that the temperature of the tray can be as low as -40C. and as high as +40C. or more. The frozen yogurt i9 now dried for a sufficient period of time until most of the water is removed. The dried yogurt i5 powdered and can be kept on tha shelE at room temperature for at leas~ 6 months or longer without deterioration.
The composition of the dry yogurt powder is as follows:

Protein (N x 6.38) 35.23 Carbohydrate (reducing sugars)33.10 Fat (Soxlet) 0.56 Moisture (oven) 5.00 Ash (funlace) 8.19 Other ~difference)` 17.92 Total 100.00 Titratable acidity (meg/100 g) 103.66 Aerobic colony count (/g) 310 Coliforms (MPN/g)Nil Staph (/g) C50 Salmonella Negative The dried yogurt powder can be reconstit~lted by adding the desired amount of tap water, resulting ~n a smooth creamy substance with the same qualities as the true natural yogurt made before freeze drying.
In one example, to make one serving of yogurt, take 30 gm of powder, add 150 gm of water and mix thoroughly. The yogurt can be either eaten immediately or cooled in a refrigerator depending on the preference. Fruit or any other flavouring can be added to the yogurt after reconstitution with water. The tangy typically cultured flavour of the yogurt combines well with the various fruits and yields more pleasing fruit flavour.
.. ~

.. : . . .: .. : ~ : .. ~

:. : . : :: : :

COMPOSITION OF _CONSTIT~TED INSTANT YOG~RT
Protein 8.2%
Carbohydrates 4.5%
Fat 1.0% .
Ash 2.5%
Calories 60-75 Example II - Low Calorie and ~ow Sodium Yogurt J
To 1000 grams of skim milk powder, 2600 gm water is added and thoroughly mixed until the skim milk powder is completely in solution. The solution is then concentrated by ultrafiltration, e.~., with an AMICON (registered Trade Mark) ultrafilter or with an AscoR
UF-225 (registered ~rade Mark) unit with ~FM (high flux membrane) or holofiber tubes with a molecular cut-off of 10,000. This system sub-; stantially eliminates molecules smaller than 10,000, which includes the sugars and minerals. The substantial elimination of sugar lowers the calories of the products. Yogurt maae from skim milk powder has 60-75 calories per 100 grams. By the above ultrafiltration process, the calories per 100 grams of yogurt will be 30-40.
Water lost during the ultrafiltration proces: may later be added, as well as essential minerals and vitamins~ However, for those who are on a low sodium diet, (essential for people with high blood pressure and kidney disease:), sodium-free yogurt may be prepared by the ultrafiltration method.
After the ultrafil~ration, the preparation of instant yogurt follows as in Example 1, lncluding heating the sol~ttion at 90C. for 15 minutes,and then cooling prior to incubation thereof.

~:

~3 ~
~,`

INSTANT YOGURT

Protein 8.2%

Carbohydrate 1.5% '~

Fat Ash 1.5%

Calories 30-35 Example III - Low Calorie Instant Yogurt Follow procedure given,in Example II. A low calorie instant ' :
yogurt is produced by passing the milk solution through a molecular sieve, ~
e.g. that known~by the Trade Mark of SEPHADEX column or that known by the ~' Trade Mar~. of BIO-GEL column. This method fractionates s1~bstances according to their molecular wieght, which are eluted off the column. The ~ugars thus coming off the column can be elimdnated. ' ._, :, ~ : :
This process also dilutes the total mixture which is concentrated by ultra-filtration'to its original volume.
The production of the instant yogurt follows the description , of Example I.;
Example IV - Plain Instant Yogurt ; ' ~
The method is the same as~for Example I, but one-third~of the skim milk powder is replaced with whey powder~ reducing drastically the cost 20 ~ of the final product.

`

:

13 -~
~' ~

~L~L~'~V

The composition oE the whey used was as follows:
Typical Chemical ~nalysis ~-Carbohydrate (lactose) 73.0%, minimum 70%
Proteins 12.5%, minimum 12.0%
Minerals 8.0%~ maximum 9.0% .
Moisture 3.5%, maximum 5.0%
Lactic Acid 1.4%, maximum 2.5%
Fat 1.0%, maximum 1.25%
Colour Uniform light cream colour.

Texture Free from lumps. that do not break up under moderate pres-sure.
Soluhility Index 0,3, maximum 1.25j50 ml Sediment (scorched particles) Equal to standard chart Disc B
Microbiological Analysis Standard Plate Count less than 50,000/gm Coliform less than 50/gm E. Colî negative Salmonella negative L33~

The composition of the dry yogurt powder was as follows: :
Protein (N x 6.38) 28.04 Carbohydrate (reducing sugars) 32.20 Fat (Soxlet~ ~ 1.03 Uoisture (oven) 11.4Z
Ash (furnace~ 8.67 ~` Other ~difference~ 18.64 Total 100.00 Titratable acidity (meg/100 g~ 90.20 Aerobic colony count (/g) 460 : Coliforms (MPN/g~ ~ Nil Staph (ig) ~50 Salmonella Negative , :

: :

. ~.
~.

`: : : :

. . .

~" , : : : :

~, .
:,,

Claims (13)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for preparing a powder which can be instantly reconstituted to a true natural yogurt, said process comprising:
(1) innoculating a liquid milk product with sufficient bacterial mixture of Lactobacillus bulgaricus and Streptococcus thermophilus in a ratio of 0.5:1 to 1.5:1 and incubating said innoculum at a temperature of 41 - 46°C. for a sufficient amount of time to provide a solution having a pH of 4.3 - 4.4;
(2) subjecting the yogurt so prepared to sub-zero temperatures until said yogurt is frozen to a temperature below its eutectic point;
and (3) removing substantially all the water from said frozen yogurt in a closed environment subjected to low absolute pressure and a heat input within a controlled temperature range of -40°C. to +40°C. and having a condensing surface therein maintained at a temperature below -40° to -80°C., and converting said freeze-dried yogurt to particulate form, thereby to provide a shelf-stable powdered yogurt.

2. The process of claim 1 wherein said liquid milk product is skim milk.

3. The process of claim 1 wherein said liquid milk product is reconstituted skim milk provided by dissolving skim milk powder in water.

4. The process of claims 1, 2 or 3 wherein said innoculating step includes incubating said innoculum with said Lactobacillus bulgaricus and Streptococcus thermophilus at a ratio of 1:1 for a period of 4 - 6 hours at a temperature of 41 - 46°C., and then incubating said partially incubated innoculum at a temperature of 36 - 38°C. for a further period of 2 - 4 hours, thereby to provide variations in texture, taste and aroma in the yogurt so-produced.

5. The process of claims 1, 2 or 3 wherein said innoculating step includes innoculating with an amount of a bacterial mixture amounting to 2% of the volume of the liquid milk product of Lactobacillus bulgaricus and Streptococcus thermophilus in a ratio of 1:1, and including from 0.5 - 1.5%
by weight thereof of Lactobacillus acidophilus, thereby to provide variations in flavour in the yogurt so-produced.

6. The process of claim 3 wherein said reconstituted skim milk solution is heated to 85 - 95°C. for 10 - 20 minutes and is then cooled to 41 - 46°C. prior to being inoculated.

7. The process of claim 3 wherein up to one-third of the skim milk powder is replaced with whey powder.

8. The process of claims 1, 2 or 3 including the step of subjecting the liquid milk product to ultrafiltration prior to being inoculated, thereby substantially to eliminate molecules having a molecular weight less than 10,000

9. The process of claims 1, 2 or 3 including the step of passing the liquid milk product through a molecular sieve prior to being inoculated, thereby substantially to eliminate molecules having a molecular weight less than 10,000.

10. The process of claims 1, 2 or 3 including the step of adding fruit or other flavourings to the yogurt prior to being subjected to steps (2) and (3).

11. A dried yogurt whenever prepared by the process of claims 1, 2 or 3 or by its obvious chemical equivalents, and having the following composi-tion:

12. A dried yogurt whenever prepared by the process of claims 1, 2 or 3 or by its obvious chemical equivalents, and having the following com-position:

and also containing freeze-dried fruit therein.

13. An instantly reconstituted true natural yogurt prepared by add-ing water to a dried powdered yogurt when prepared by the process of claims 1, 2 or 3 by its obvious chemical equivalents, to provide a true natural yogurt having the following composition: