Technology and stages of production of fermented milk products. Coursework: Technology of liquid fermented milk products and drinks

Dairy products- a group of dairy products produced from whole cow's milk, milk of sheep, goats, mares and other animals or its derivatives (cream, skimmed milk and whey) by fermentation.

Manufacturing technology of fermented milk products consists of the preparation of raw materials, the normalization of milk or cream in terms of fat, heat treatment, homogenization, cooling to the fermentation temperature, the process of fermentation, fermentation and cooling to a temperature not exceeding +8 °C.
There are two methods for the production of fermented milk products: thermostatic and reservoir.

At thermostatic method the milk is purified, normalized, pasteurized or sterilized, homogenized, cooled to the fermentation temperature and then fermented. Fermented milk (or cream) is poured into packaging (bottles, jars, etc.), corked and placed in thermostatic fermentation chambers. Then the product is cooled in a cold chamber to +8 °C and kept for maturation from 6 to 12 hours.

In the production of fermented milk products from skimmed milk or buttermilk, they are not standardized and homogenized.

Using reservoir method fermentation and fermentation of milk, cooling and maturation of the product takes place in large tanks (tanks) and the finished product is poured into the package. With this method, purified milk is heated to +72 ... 75 ° C and sent for pasteurization. Then it is kept for 10 minutes and fed into a homogenizer, in which it is processed under pressure.

Homogenized milk is cooled to +22 °C and sent for fermentation. Depending on the type of starter, fermentation lasts from 2.5 to 7 hours. After the formation of a clot and the achievement of the required acidity, the products are immediately cooled to a temperature not exceeding +8 ° C, and then poured into a package. The reservoir method for obtaining fermented milk products is more economical than the thermostatic one, the product quality is higher.

Fermented milk products are divided according to the nature of the fermentation that occurs during the fermentation of milk (cream, whey, buttermilk).

There are two dairy product groups:
1. products obtained as a result of only lactic acid fermentation (ordinary and Mechnikov yogurt, boiled milk, fermented baked milk, acidophilus milk, yogurt, etc.);
2. products obtained by mixed fermentation - lactic acid and alcohol (kefir, koumiss, acidophilus-yeast milk).

In the first group, bacteria break down milk sugar with the formation of lactic acid, under the influence of which milk casein coagulates (falls out in the form of flakes), as a result of which digestibility, compared with milk, is significantly increased. The products of this group have a sour-milk taste, a fairly dense and homogeneous clot without gas bubbles.

In the products of the second group, along with lactic acid, alcohol, carbon dioxide, volatile acids are formed from milk sugar, which also increase the digestibility of the product. The products of this group have a sour-milk taste, but a sharper, “pinching”, refreshing and tender clot, riddled with small gas bubbles. The clot easily breaks when shaking or stirring, as a result of which the consistency of the product becomes creamy, homogeneous. Therefore, such products are called drinks.

Fermented milk products include whey drinks, but they do not have a clot due to the lack of protein - casein. In terms of protein and fat content, fermented milk products almost do not differ from whole milk.

Also often fermented milk products are enriched with various probiotic cultures. The most famous example is bifidok, which differs from kefir by the addition of bifidobacteria.

At production of fermented milk products use pure cultures of lactic acid bacteria. Pure cultures include lactic streptococcus (Str. Lactis), Bulgarian bacillus (Bad. Bulgaricum), acidophilus bacillus (Bad. Acidophilum), aroma-forming bacteria (Str. Diacetiladis) and lactic yeast (Torula).

Each product is made using certain cultures of microorganisms. The most used for production are lactic streptococci, which develop at different temperatures: mesophilic - + 30 ... 35 ° C, thermophilic - + 42 ... 45 ° C with an acid formation limit - 120 ... 130 ° T.

Bacillus bulgaris and acidophilus are thermophilic bacteria. Bacillus bulgaris and nonmucous races of acidophilus bacillus are strong acid formers.

For the production of kefir, kefir fungi are used, the microflora of which consists of a combination of lactic acid streptococci and rods, aroma-forming bacteria, lactic yeast, mycoderma and acetic bacteria. Kefir grains serve as the parent starter from which all subsequent starters for the production of kefir are obtained.

starter cultures, used for a significant accumulation of lactic acid, are prepared using homofermentative microorganisms (lactic acid streptococci, Bulgarian, lactic acid, acidophilus and other sticks).

When using heterofermentative bacteria that form lactic acid, as well as ethyl alcohol, acetic, propionic and valeric acids, diacetyl, acetoin, acetaldehyde, a specific taste and aroma of products is formed.

In the production of cottage cheese ripening occurs as a result of the vital activity of sourdough microorganisms and the action of the introduced rennet (powder from the mucous membrane of the fourth section of the stomach - the abomasum of dairy calves and lambs). After fermentation, the process of separating the whey from the clot takes place.

The quality of fermented milk products strongly depends on the composition of the starter culture. When using energetic acid-forming agents (lactic acid streptococcus, Bulgarian bacillus), lactic acid accumulates significantly and a dense clot is obtained with an intensive release of whey. When using weak acid-forming agents (aroma-forming streptococci), a delicate clot with a pleasant aroma and taste is obtained.

Prevent the separation of whey, increase the viscosity and elasticity of the product creamy streptococcus and acidophilus bacillus. Yeast, aroma-forming and acetic acid bacteria release carbon dioxide, which contributes to the destruction of the clot. Increases the strength of the clot and reduces the intensity of whey separation by increasing the pasteurization temperature of milk.

In the production of kefir, curdled milk, sour cream, the process of homogenization of milk and cream accelerates the formation of a clot, increases its viscosity and plasticity, and reduces the release of whey. But this process is impractical in the production of cottage cheese.

The temperature regime and the duration of mowing depend on the microflora in the composition of the starter cultures: when using kefir starter culture - 8-12 hours, thermophilic bacteria - 2.5-4 hours, mesophilic species - 5-7 hours. The end of fermentation is determined by the strength of the clot and titratable acidity. Cooling and ripening of sour cream lasts 6–48 hours, depending on the packaging.

MINISTRY OF YOUTH EDUCATION AND SPORTS

TECHNICAL UNIVERSITY OF MOLDOVA

Department of Technology and Public Catering

Course work

According to the technology of milk processing on the topic:

"Technology of liquid fermented milk products and drinks"

Performed:

Student gr. TL-052

Checked:

Senior Lecturer Popescu L.

Chisinau 2009

Introduction

1. Assortment of liquid fermented milk products.

Terms and definitions…………………………………..3

2. Finished product quality indicators………….5

3. General technology………………………………………….8

4. Theoretical foundations of production………………10

5. The influence of various factors on the production process..14

6. Vices……………………………………………………… 17

Bibliography.

Introduction

The national fermented milk product is a fermented milk product that has a historically established name in the country, depending on the type of starter culture and specific technology.

Fermented milk products include liquid fermented milk products and drinks, as well as cottage cheese and cottage cheese products and sour cream. Liquid fermented milk products and drinks include the following products.

1. Assortment of liquid fermented milk products .

curdled milk - a national fermented milk product made by fermenting milk with pure cultures of lactococci and / or thermophilic lactic streptococci, the total content of which in the finished product at the end of the shelf life is at least 107 CFU per 1 g of the product, without the addition of non-dairy components.

Mechnikovskaya prostitute - a national fermented milk product made by fermenting milk with pure cultures of thermophilic lactic acid streptococci and lactic acid bulgarian sticks, the total content of which in the finished product at the end of the shelf life is at least 107 CFU per 1 g of the product, without the addition of non-dairy components.

Ryazhenka - a national fermented milk product made by fermenting baked milk with pure cultures of thermophilic lactic streptococci, the total content of which in the finished product at the end of the shelf life is at least 107 CFU per 1 g of the product, without the addition of non-dairy components.

Varenets - a national fermented milk product made by fermenting milk sterilized or heat treated at a temperature of (97 ± 2) ° C for 40 to 80 minutes with pure cultures of thermophilic lactic streptococci, the total content of which in the finished product at the end of the shelf life is at least 107 CFU in 1 g of the product, without the addition of non-dairy components.

Kefir - a national fermented milk product of mixed lactic and alcoholic fermentation, made by fermenting milk with sourdough prepared on kefir fungi without the addition of pure cultures of lactic acid bacteria and yeast, the content of lactic acid microorganisms in the finished product at the end of the shelf life is at least 107 CFU per 1 g of the product, and yeast not less than 104 CFU per 1 g of the product, without the addition of non-dairy components.

acidophilus - a national fermented milk product made by fermenting milk with pure cultures of lactic acidophilus bacillus, lactococci and sourdough prepared on kefir fungi in equal proportions, the total content of lactic acid microorganisms in the finished product at the end of the shelf life is at least 107 CFU per 1 g of the product, without the addition of non-dairy components.

Airan - a national fermented milk product of mixed lactic acid and alcoholic fermentation, made by fermenting milk with pure cultures of thermophilic lactic acid streptococci, lactic acid bulgarian bacillus and yeast, the content of lactic acid microorganisms in the finished product at the end of the shelf life is at least 107 CFU per 1 g of the product, and yeast is at least 104 CFU per 1 g of the product, without the addition of non-dairy components.

Kumys - a national fermented milk product of mixed lactic and alcoholic fermentation, made by fermenting mare's milk with pure cultures of Bulgarian and acidophilic lactic acid bacilli and yeast, the content of lactic acid microorganisms in the finished product at the end of the shelf life is at least 107 CFU per 1 g of the product, and yeast is at least 105 CFU in 1 g of the product, without the addition of non-dairy components.

Yogurt - a fermented milk product with a high content of skimmed milk solids, produced by fermenting with a protosymbiotic mixture of pure cultures of thermophilic lactic acid streptococci and lactic acid bulgarian sticks, the content of which in the finished product at the end of the shelf life is at least 10 7 CFU per 1 g of the product (adding food additives is allowed , fruits, vegetables and products of their processing).

1.1. Classification of liquid fermented milk products and drinks

Fermented milk drinks, depending on the milk raw materials from which they are produced, are divided into products :

From natural milk;

From normalized milk;

From reconstituted milk;

From recombined milk;

from their mixtures.

Sour-milk drinks, depending on the mass fraction of fat, are divided into products :

Fat-free (m.d.zh.,%, 0.1);

Non-fat (m. d. w.,%, 0.3; 0.5; 1.0);

Low-fat (m.d. w.,%, 1.2; 1.5; 2.0; 2.5);

Classical (m. d. w.,% 2.7; 3.0; 3.2; 3.5; 4.0; 4.5);

Fat (m. f.,%, 4.7; 5.0; 5.5; 6.0; 6.5; 7.0);

High-fat (m. f.,%, 7.2; 7.5; 8.0; 8.5; 9.0; 9.5).

2. Indicators of the quality of the finished product .

According to organoleptic indicators, fermented milk drinks must meet the requirements indicated in Table 1

Table 1

Organoleptic characteristics of fermented milk drinks

According to physical and chemical indicators, fermented milk drinks must meet the requirements specified in Table. 2

table 2

Physico-chemical indicators of fermented milk products

Phosphatase is not allowed in the product.

Table 3

Microbiological indicators of fermented milk drinks are shown in table. four

Table 4

Microbiological indicators of fermented milk drinks

For the manufacture of fermented milk drinks, the following raw materials are used :

raw cow's milk not lower than the second grade according to GOST E52054; whole milk powder of the highest grade according to GOST 4495; skimmed milk powder according to GOST 10970; cream powder according to GOST 1349; unsalted butter according to GOST 37; starter cultures based on pure cultures of lactic acid microorganisms produced according to TU 9229-369-0019785-04 “Start cultures, bacterial concentrates, yeast and test cultures”; drinking water according to SanPiN 2.1.4.1074 (for recombined or reconstituted milk).

3.General technology of fermented milk products .

Milk and other raw materials are accepted according to the weight and quality established by the quality control department (laboratory) of the enterprise, as well as on the basis of certification documents of supplier firms.

Immediately after taking the milk

1. warm up to a temperature of 35 ... 40 ° C and cleaned on centrifugal milk cleaners or other equipment without heating. To purify raw milk, it is also recommended to use a bacteriophage with a specially built hermetic separator to remove bacteria from the milk.

2. After this milk is sent for processing or cooled to a temperature of (4 ± 2) °C and stored in intermediate storage tanks. Storage of milk, cooled to a temperature of 4 °C, before processing should not exceed 12 hours, cooled to a temperature of 6 °C-6 hours.

3. Selected quality milk normalize by mass fractions of fat and protein in such a way that they in the finished product are not less than those provided by the standard.

Normalization, as well as the preparation of butter, the restoration of dry dairy products is carried out in the same way as it was shown in the technology of drinking milk.

4. normalized mixture warm up to a temperature of (43 ± 2) °С and cleaned on centrifugal milk cleaners or filters.

5. Purified milk homogenize at a pressure of (15.0 ± 2.5) MPa at a temperature of 45 to 85 °C. If necessary, it is allowed to homogenize milk at the pasteurization temperature.

Instead of complete homogenization, it is allowed to use separate homogenization of milk. When using separate homogenization, milk normalized for fat and heated in the second regeneration section of the plate pasteurizer to a temperature of 55 ... 65 ° C is separated. In this case, the mass fraction of fat in the resulting cream is from 16 to 20%. The resulting cream is homogenized in a two-stage homogenizer at a pressure: in the first stage from 8 to 10 MPa, in the second - from 2 to 2.5 MPa. The homogenized cream in the stream is mixed with the skimmed milk leaving the cream separator and sent to the pasteurization section.

In order to improve the taste of fermented milk drinks, it is also recommended to homogenize the milk intended for their production with a mass fraction of fat less than 2.5%.

6. Purified and homogenized mixture pasteurized at a temperature of (92 ± 2) °C with an exposure of 2 to 8 minutes or (87 ± 2) °C with an exposure of 10 to 15 minutes. Milk can be kept at these temperatures for 30 to 40 minutes. In the production of ryazhenka, milk is pasteurized at temperatures from 95 to 99 ° C with an exposure of 3 to 4 hours until a pronounced light cream color, and Varentsa - at the same temperatures with an exposure of 60 to 80 minutes.

In the production of ryazhenka, it is necessary to take into account the degree of bacterial contamination, composition, thermal stability of raw materials, etc. It is allowed to pre-pasteurize the normalized mixture at a temperature of (76 ± 2) ° C, followed by heating to a temperature of 95 ... 99 ° C with holding from 3 to 4 hours to a pronounced light cream color. Moreover, during heating, the mixture is stirred 1-2 times per hour to prevent the formation of foam.

7. After pasteurization and aging milk chilled to fermentation temperature : (40 ± 2) °С or (30 ± 2) °С in the production of curdled milk; (42 ± 2) °С in the production of Mechnikovskaya curdled milk, yogurt, fermented baked milk, Varenets, etc.; (37 ±2) °С in the production of acidophilic fermented milk drinks; from 18 to 25 ° C in the production of kefir, etc., that is, to a temperature that is optimal for the development of microflora used in the production of a particular fermented milk drink. Storage of the unfermented mixture at the fermentation temperature is not allowed.

With the tank method of production, milk is fermented and fermented in tanks for fermented milk drinks with a cooling jacket, equipped with special agitators that ensure uniform and thorough mixing of milk with ferment and fermented milk clot. To avoid foaming, which affects the separation of whey during the storage of fermented milk drinks, milk is fed into the tank through the lower fitting.

The starter is prepared in accordance with the current technological instructions for the preparation and use of starters and bacterial concentrates for fermented milk products at dairy industry enterprises, approved in the prescribed manner.

The starter is introduced into milk in a stream using a dosing pump simultaneously with milk, or after some time from the start of filling the tank, or after filling the tank. The volume fraction of the starter in relation to the volume of the fermented mixture prepared with sterilized or pasteurized milk is 3...5%. During the introduction of the starter, the milk must be stirred to evenly distribute the starter in the volume of the product and prevent the formation of protein flakes. Milk with added starter is stirred for 10 ... 15 minutes.

With the tank method of production, after mixing, the fermented milk is left alone for fermentation. It is allowed to re-mix in 1...1.5 hours after fermentation.

With the thermostatic method of production, milk is fermented in tanks for fermented milk drinks with a cooling jacket, equipped with special agitators that ensure uniform and thorough mixing of milk with ferment. Fermented milk is immediately poured into consumer containers with continuous stirring. Filling from each tank must be completed within 45-60 minutes to avoid the formation of coagulated protein flakes. The mixture is fermented in a thermostatic chamber at the temperature indicated below.

The temperature and duration of fermentation in the production of fermented milk drinks is different depending on the microflora of the used starter. The modes are the same in the production of the same type of fermented milk drink by tank or thermostatic production methods. The end of fermentation is determined by the nature of the clot and its acidity. The clot should be smooth, sufficiently dense and not secrete serum. Temperature and duration of fermentation:

In the production of curdled milk - for 5 to 7 hours at a temperature of (30 ± 2) °С and from 3 to 4 hours at a temperature of (40 ± 2) °С

when using dry bacterial concentrate of lactococci, milk is fermented at a temperature of (30 ± 2) °С from 8 to 10 hours, when using dry bacterial concentrate of thermophilic lactococcus - at a temperature of (40 ± 2) °С from 6 to 8 hours; I in the production of ryazhenka, yogurt, Mechnikov yogurt, varenets, etc. - for 4 to 6 hours at a temperature of (40 ± 2) ° C or when using dry bacterial concentrate - for 8 ... 10 hours at a temperature ( 40 ± 2) °С;

in the production of acidophilic fermented milk drinks - for 7...9 hours at a temperature of (37 ± 2) °C;

in the production of kefir - for 8 to 12 hours at a temperature of 18 to 25 °C. In addition, in the production of kefir, the fermented mixture is matured for 9 to 13 hours at a temperature of (14 ± 2) °C.

Fermented mixtures are fermented until a milk-protein clot and acidity are formed: from 75 to 80 °T in the production of curdled milk; from 65 to 70 °T - in the production of fermented baked milk; from 85 to 100 tons - in the production of kefir, etc.

8. At the end of fermentation in the tank method of production, the supply of ice water with a temperature of (2 ± 2) ° C is included in the interwall space of the tank for partial cooling of the clot to a temperature: in the production of sour milk - 25 ... 35 ° C, in the production of fermented baked milk - (22 ± 5 ) °С; in the production of kefir - (14 ± 2) ° С

In the tank method of production, after a period of 60 to 90 minutes after water supply, the mixer is turned on and the curd is stirred for 10 to 30 minutes, depending on the design of the mixer and the viscosity of the curd, to obtain a uniform consistency of the curd. When storing fermented milk drinks with a heterogeneous, lumpy consistency, whey may be released. Further mixing, if necessary, is carried out periodically, including the stirrer for 5 ... 15 minutes.

In the production of kefir, the milk clot mixed and cooled to a temperature of (14 ± 2) ° C is left alone for maturation for a period of 9 to 13 hours. It is allowed to send a mixed and partially cooled clot for bottling, followed by maturation and cooling of the packaged kefir in a refrigerator. From the moment of fermentation to the end of ripening, at least 24 hours must pass.

2 to 5 minutes - in the production of kefir or within 5 to 15 minutes - in the production of fermented baked milk and curdled milk.

When mixing, pumping and pouring a fermented milk clot, it is recommended to avoid intense mechanical impact (long narrow pipelines, pumps, leading to significant damage to the clot, etc.), air leakage, which adversely affect the quality of the finished product. It is desirable to pour the fermented clot by gravity with a minimum level difference in height.

The mixed clot is fed with a pump designed for viscous liquids for bottling into consumer containers. In the presence of plate coolers, the clot can be cooled to a temperature of (4 ± 2) °C before bottling.

9. The packaging and labeling of fermented milk drinks is carried out in accordance with the requirements of the current standard for this product. The duration of bottling the fermented product from one container should not exceed 2 hours.

The packaged fermented milk drink, if necessary, is additionally cooled in the refrigerator to a temperature of (4 ± 2) °C, after which the technological process is considered complete and the product is ready for sale.

With the thermostatic method of production, after fermentation, the packaged product is placed in a refrigerator and cooled to a temperature of (4 ± 2) °C. In the case of the production of kefir in the refrigerator for 8 ... 13 hours, the milk-protein clot matures. After that, the technological process is considered complete and the product is ready for sale.

4. Theoretical foundations of production

The production of fermented milk products is a complex biochemical process, as a result of which the taste and smell, texture and appearance peculiar only to this fermented milk product are formed. Fermented milk products are obtained by fermenting heat-treated milk, cream, buttermilk, whey, or mixtures thereof.

According to GOST 51917, a fermented milk product is a dairy product made by fermenting milk or cream with kefir fungi and / or pure cultures of lactic acid, propionic acid, acetic acid microorganisms and / or yeast and / or their mixtures. The total content of lactic acid microorganisms in the finished product at the end of the shelf life is not less than 107 CFU per 1 g of the product. After fermentation, the use of food additives, fruits, vegetables and products of their processing is allowed. Bifidoproduct is a product containing bifidobacteria, the amount of which at the end of the expiration date is not less than 106 CFU per 1 g of the product.

The technological process for obtaining fermented milk products includes the following general operations:

• normalization of milk raw materials by fat, in the production of kefir - additionally by protein, yogurt - by mass fraction of milk solids;
• heat treatment,
• homogenization
• fermentation and fermentation,
• cooling
• packaging.

In the production of fermented milk products, both biochemical and physico-chemical processes are carried out

• milk sugar fermentation,
• casein coagulation
• gelation.

BIOCHEMICAL AND PHYSICO-CHEMICAL PROCESSES IN THE PRODUCTION OF FERROUS DAIRY PRODUCTS

Dairy products play an important role in the nutrition of people, especially children, the elderly and the sick. The dietary properties of fermented milk products are primarily that they improve metabolism, stimulate the secretion of gastric juice and stimulate appetite. The presence in their composition of microorganisms that can take root in the intestine and suppress the putrefactive microflora leads to inhibition of putrefactive processes and the cessation of the formation of toxic protein breakdown products that enter the human blood

FERMENTATION OF MILK SUGAR

The most important biochemical process that occurs during the production of fermented milk products is the fermentation of milk sugar caused by microorganisms of bacterial starter cultures. Its speed and direction determine the consistency, taste and smell of finished products according to the nature of milk sugar fermentation, fermented milk products can be divided into two groups. The first group includes products, the preparation of which is mainly lactic fermentation (yogurt, yogurt, acidophilus, cottage cheese, sour cream), the second group - products with mixed fermentation, in the manufacture of which lactic and alcoholic fermentation occurs (kefir, koumiss, acidophilic - yeast milk).

During lactic acid fermentation, each pyruvic acid molecule formed from a glucose molecule is reduced with the participation of the redox enzyme lactate dehydrogen-1 to lactic acid:

By increasing the acidity of milk during lactic acid fermentation, you can calculate how much milk sugar was fermented. For example, the acidity of milk increased by 60T (acidity of fresh milk was 17°T, after fermentation of milk sugar - 77T). 1˚T corresponds to I cm3 0.1 n. alkali solution or 1 cm30.1 n. lactic acid solution, which is 90 / (10 1000) \u003d 0.009 g of lactic acid. Therefore, 60T will correspond to 600.009 - 0.54 g of lactic acid.

From the total reaction of lactic acid fermentation, it follows that 4 moles of lactic acid are formed from 1 mole of milk sugar, i.e., 4-90 = 360 g of lactic acid is formed from 342 g of lactic acid. Therefore, to obtain 0.54 g of lactic acid, milk sugar was required

Many lactic acid bacteria during the fermentation of sugar, in addition to lactic acid, form a number of other chemicals that give fermented milk products a specific taste and aroma. These include volatile acids (acetic, propionic, etc.), carbonyl compounds (diacetyl, acetoin, acetaldehyde), alcohol and carbon dioxide.

Depending on the products accumulated during the fermentation process, all lactic acid bacteria are divided into homofermentative and heterofermentative. Lactic acid bacteria (lac. lactis, Lac. cremoris, Lac. diacetilactis, Str. thermophilus, L. bulgaricus, L. acidophilus), which form lactic acid as the main fermentation product, are classified as homo-enzymatic; bacteria (Leuc. cremoris, Leuc. dextranicum, etc.), which, in addition to lactic acid, form other fermentation products in significant quantities, are heterofermentative.

By certain combination of various types of lactic acid bacteria and regulation of the fermentation temperature, it is possible to obtain a product with the desired taste, aroma, texture and dietary properties.

In fermented milk products with mixed fermentation (kefir, koumiss, etc.), along with lactic acid, a large amount of ethyl alcohol and carbon dioxide is formed. The causative agent of alcoholic fermentation in these products is yeast. During alcoholic fermentation, pyruvic acid, under the action of the enzyme pyruvate decarboxylase, which catalyzes the elimination of carbon dioxide, is split into acetaldehyde and carbon dioxide:

Acetic aldehyde with the participation of the redox enzyme alcohol dehydrogenase is reduced to ethyl alcohol:

The ability of yeast to produce alcohol and carbon dioxide depends on many factors: the type of yeast used, the amount of milk sugar in the feedstock, temperature, pH, etc.

COAGULATION OF CASEIN AND GEL FORMATION

The accumulation of lactic acid during lactic acid fermentation of lactose is essential for the formation of a protein clot that determines the consistency of fermented milk products. The essence of acid coagulation is as follows. The resulting (or added) lactic acid reduces the negative charge of casein micelles, since H-ions inhibit the dissociation of casein carboxyl groups, as well as phosphoric acid hydroxyl groups. As a result, this achieves equality of positive and negative charges and the isoelectric point of casein (pH 4.6-4.7).

With acid coagulation, in addition to reducing the negative charge of casein, the structure of the caseinate-calcium phosphate complex is disturbed (calcium phosphate and structure-forming calcium are split off). Since calcium and calcium phosphate are important structural elements of the complex, their transition into solution additionally destabilizes casein micelles.

In the production of cottage cheese by the acid-rennet method, lactic acid and the introduced rennet are jointly acting on casein.

Under the action of rennet, casein is converted into paracasein, which has an isoelectric point in a less acidic environment (pH 5-5.2).

At the isoelectric point, casein or para-casein particles aggregate upon collision, forming chains or threads, and then a spatial grid, into the cells or loops of which the dispersion medium with fat globules and other components of milk is captured. gelation occurs. In the production of fermented milk products and cheese, the gelation process can be divided into four stages: the stage of latent coagulation (induction period), the stage of mass coagulation, the stage of structure formation (clot compaction) and the stage of syneresis.

In colloidal systems, gelation is affected by the concentration of the dispersed phase, size, shape of particles, temperature, etc. The resulting clot (gel) has certain mechanical properties: viscosity, plasticity, elasticity and strength. These properties are associated with the structure of the system, so they are called structural-mechanical or rheological.

Structural and mechanical properties of clots are determined by the nature of the bonds that arise between protein particles during the formation of the structure. Relationships can be reversible or irreversible. Reversible (thixotropic-reversible) bonds are restored after disruption of the clot structure. They cause the phenomenon of thixotropy (Fig. 1a) ((Greek thixis - touch + trope - change) - the ability of structures after their destruction as a result of some mechanical action to spontaneously recover in time.

Irreversible (irreversibly destroyed) bonds do not have the ability to recover after mechanical action on the clot. They are associated with the phenomenon of syneresis. Syneresis (Fig. 1b) - compaction, contraction of the clot with shortening of the casein threads and displacement of the liquid enclosed between them. Figure 2. The speed of syneresis is determined by the water-retaining capacity of casein and depends on the concentration of dry substances in the raw material, the composition of bacterial starter cultures, homogenization heat treatment modes, the method of milk coagulation and other factors.

For fermented milk drinks and sour cream, syneresis is an undesirable phenomenon. Therefore, in their production, bacterial starters of the desired composition are used and the technological process is carried out under conditions that prevent the occurrence of syneresis. In the production of cottage cheese, on the contrary, it is required to remove excess whey from the clot. Therefore, such milk processing modes are chosen that would contribute to obtaining a dense, but easily releasing whey clot. To enhance syneresis, grinding, heating of the clot, etc. are also used.

The nature of the bonds in the structure of the clot (product) can be determined by measuring the so-called effective viscosity - the viscosity due to the formation of internal structures in the product. At the same time, the effective viscosity of the undestroyed η n, destroyed ηr and restored ηp structures is determined and compared with each other (Table 5)

As can be seen from Table 5, during the formation of clots of curdled milk and fermented milk drinks, irreversibly collapsing (non-thixotropic bonds) are mainly formed. There are few thixotropic bonds characterized by spontaneous recovery after mechanical action. Sour cream is characterized by a lower loss of viscosity during the destruction of the structure and a large number of thixotropic bonds compared to sour-milk drinks.

Table 5

BIOCHEMICAL BASES OF PRODUCTION CERTAIN TYPES OF FERROUS MILK PRODUCTS

The quality of fermented milk products produced depends on the nature of the formed clots, as well as the degree of accumulation of flavoring and aromatic substances. The nature of the clots is determined by the level of accumulation of lactic acid, the ability of proteins to form spatial structures, retain moisture, etc. The formation of flavoring and aromatic substances depends on the composition of bacterial starter cultures, the conditions of fermentation, maturation and cooling of products.

fermented milk drinks

The main process that determines the consistency of all fermented milk drinks is gelation. The clots of these products are different: in some cases, the clot is dense (prickly), in others it is even and tender (creamy) or flaky, etc.

When forming the structure of product clots, irreversibly breaking bonds are mainly formed, there are few thixotropic-reversible bonds in them, therefore it is so important to conduct the technological process under such modes that would ensure minimal separation from the whey clot. First of all, this applies to the modes of pasteurization, homogenization and fermentation of milk.

It is known that the syneretic properties of clots depend on the pasteurization temperature of milk. To increase the strength of clots and prevent the release of whey during storage of curdled milk and other fermented milk drinks, it is recommended to use high temperatures for pasteurization of milk (85-87°C with exposure for 5-10 minutes or 90-94°C with exposure for 2-8 minutes).

The duration of fermentation of milk during the development of products is determined by the type of bacterial starter and the fermentation temperature. The end of fermentation is usually set to obtain a sufficiently strong clot and titratable acidity of 75-85°T. In the production of fermented milk drinks by the tank method, it is necessary to obtain a clot with the maximum number of thixotropic-reversible bonds, therefore, before mixing and cooling the clot, the pH (pH) should be controlled: it should be 4.5-4.4 for kefir, 4.7-4.7 for acidophilus. 4.55, ryazhenka - 4.45-4.35. Additionally, the viscosity of the clot is checked by the duration of the flow from a pipette with a capacity of 100 cm 3 at 20 ° C or using a capillary viscometer.

Specific sour-milk taste and smell of products are formed mainly during their fermentation and maturation. Complementing the taste and smell of products are compounds formed during the heat treatment of milk (they play a major role in the production of Varenets and fermented baked milk).

The main flavoring and aromatic substances of fermented milk products are lactic and acetic acids, diacetyl, acetaldehyde (its high concentration is typical for yogurt), etc. Refreshing, slightly spicy taste of koumiss and kefir is given by ethyl alcohol and carbon dioxide. The alcohol retention in beverages is determined by the type of yeast, temperature and length of maturation. In koumiss, it is 1 - H "6, in kefir - 0.01-0.03%. They are also characterized by protein breakdown (proteolysis), so the released amino acids and peptides can take part in shaping the taste of these products.

5 . INFLUENCE OF MILK COMPOSITION, BACTERIAL STARTERS AND OTHER FACTORS ON FERTILIZATION LACTOSE AND CASEIN COAGULATION

The quality of fermented milk products, mainly their consistency, depends on the composition and properties of milk, the type and activity of bacterial starters, the modes of pasteurization, homogenization, fermentation, maturation, and other factors.

Composition and properties of feedstock determine the rate of coagulation of milk proteins and the strength of the resulting clots. The development of microorganisms of bacterial starter cultures that ferment milk sugar also depends on them.

The composition and properties of milk change during the year, the stage of lactation, in case of animal diseases, etc. It is known from the practice of dairy plants that in autumn and especially in spring, milk is slowly fermented. This may be due to a decrease in its biological value. For example, in spring the content of vitamins (biotin, niacin, B6, etc.), free amino acids (valine, leucine, phenylalanine, etc.) and microelements (Mn, Co, Fe, etc.), which are necessary for the reproduction of lactic acid bacteria, decrease in milk. bacteria. In addition, the reason for non-fermentation of milk at this time of the year may be the presence of antibiotics and other substances in it that inhibit the development of lactic acid bacteria. Lactic acid bacteria develop poorly in old milk and in milk obtained from cows with mastitis.

In the spring, the technological properties of milk also deteriorate - the rate of formation and density of the acid clot decrease. This is due to a decrease in the content of dry substances in milk, casein, the size of casein micelles, and an increase in the acidity of milk.

· Individual characteristics and breeds of animals

The ability of milk to rennet coagulation is determined by the concentration of proteins, calcium salts and depends on the individual characteristics and breed of animals, feed, stage of lactation and other factors. Milk coagulates poorly at the beginning and end of lactation, as well as when animals are sick.

· Storage time

The properties of milk (and the properties of the clot obtained from it) change during storage. So, after long-term storage of milk (raw and pasteurized) at low temperatures, the viscosity and strength of the acid clot increase, syneresis slows down. Therefore, milk stored at low temperatures should be sent to the production of fermented milk drinks and should not be used. for making curd

· Starter composition.

Not only the taste of fermented milk products, but also their consistency depends on the composition of the starter cultures. The main component of the microflora of starter cultures of all fermented milk products, which ensures the formation of a clot, is lactococcus (Lac. lactis). The inclusion of energetic acid-forming agents in the composition of the starter cultures leads to the production of a dense prickly clot with an intensive separation of whey, and low-energy acid-forming agents - a more delicate clot. Introduction of sourdough Str. thermophilus, Lac. cremoris and thermophilic sticks increases the viscosity of the product, gives the clot elastic properties, prevents the release of whey.

Therefore, by selecting the composition of starter cultures, it is possible to regulate the properties of the clot and ensure the optimal consistency and taste of fermented milk products.

· Heat treatment

Heat treatment of milk affects the rate of clot formation, structural and mechanical properties and syneresis.

According to VNIMI and VNIIMS, with an increase in pasteurization temperature, the strength of acid and acid-rennet clots increases (Table 6).

Table 6

With an increase in the pasteurization temperature of milk (from 63 to 90" C ) the intensity of separation of whey from the clot decreases. The increase in the strength of clots and the deterioration in the release of whey from them after high temperatures of heat treatment can be explained by an increase in the content of denatured whey proteins in the clot, which increase the rigidity of the spatial structure and the water-holding capacity of casein.

Thus, by adjusting the modes of heat treatment of milk, it is possible to obtain a clot with the desired rheological properties, i.e., improve the consistency of the fermented milk product

· Milk homogenization

When producing fermented milk drinks, it is recommended to homogenize the milk before fermentation (for kefir and yogurt obtained by the tank method, it is mandatory). As a result of homogenization, the dispersion of fat increases, the crushed fat in clots is distributed more evenly, the strength of the clot increases, while the viscosity of the products slightly increases and whey release decreases.

At the same time, homogenization of milk with a high (above 10%) fat content and cream contributes to a significant increase in the viscosity of clots and a decrease in their ability to separate whey. In this case, the increase in the viscosity of the formed clots depends on the pressure and the method of homogenization of the raw material.

Structural-mechanical and syneretic properties of clots significantly depend on the method of protein coagulation

· Type of coagulation

Clots formed during acid coagulation of proteins are less strong than acid-rennet ones (the spatial structure of acid clots is supported by weak bonds, the structure of acid-rennet ones is additionally stabilized and strengthened by calcium bridges formed between the parts of paracasein); they consist of smaller protein particles and secrete serum worse. However, along with an increase in the strength of acid-rennet clots, their fragility, the degree of dispersion and the ability to separate whey during processing increase.

· Clotting time and temperature

The duration and temperature of curdling (fermentation) of milk are important factors affecting the consistency of fermented milk products. The duration of milk fermentation is usually determined by the increase in acidity, viscosity or strength of the resulting clot. It is especially important to determine the moment of clot readiness in the production of beverages by the tank method. Sometimes there is a liquid consistency of products and whey sludge. This is caused by the wrong choice of the moment of clot mixing. Whey is released when the clot is stirred when it has a minimum viscosity and exhibits slight thixotropic properties.

In addition, the accumulation in the products of substances that give them a certain taste and aroma (volatile acids, diacetyl, acetaldehyde, etc.) depends on the temperature and duration of milk fermentation.

To stop lactic acid fermentation and strengthen the structure of the formed clot, fermented milk products are cooled to 8°C and stored at this temperature. Products of mixed fermentation before cooling are subjected to maturation, for the development of yeast and aroma-forming bacteria. In the process of ripening and keeping in the refrigerator, aromatic substances, alcohol and carbon dioxide accumulate in the products, and partial decomposition of proteins occurs under the influence of proteolytic enzymes of lactic acid bacteria and yeast. At the same time, various soluble polypeptides and free amino acids are formed, which affect the texture, taste and smell of products.

In the production of sour cream, an additional purpose of cooling and ripening is the solidification of fat, which improves the structure and consistency of the product.

5. FAULTS OF FERROUS MILK PRODUCTS .

Bibliography

1 TO. K. Gorbatova "BIOCHEMISTRY OF MILK AND DAIRY PRODUCTS" St. Petersburg GIORD 2004

2.N. A. Tikhomirova "Technology and organization of production of milk and dairy products" 2007 Moscow DeLi print

In the preparation of fermented milk products, the ability of milk to ferment is used. Common in the production of all fermented milk drinks is the fermentation of prepared milk with starters and, if necessary, maturation. The specifics of the production of individual products differ only in the temperature regimes of some operations, the use of starters of different composition and the introduction of fillers.

There are two groups of dairy products. The first group consists of products obtained as a result of lactic acid fermentation (curdled milk, acidophilic milk, etc.), the second - products obtained as a result of mixed (lactic acid and alcohol) fermentation (kefir, koumiss, etc.). The taste and consistency of these products depend on many factors: the properties of milk, types of starter cultures, fermentation methods, etc. Pure cultures of lactic acid bacteria with or without the addition of cultures of lactic yeast are used as starter cultures: lactic acid streptococci, Bulgarian bacillus, acidophilus bacillus, bacteria and others.

Yogurt (ordinary, Mechnikov, Ukrainian (ryazhenka), varenets, acidophilic, southern (matsun), yogurt, etc.) differ depending on the milk used (pasteurized and sterilized), the type of lactic acid yeast.

Curdled milk production technology tank method: acceptance and evaluation of milk quality; cleaning; normalization (up to fat content of 2.5-3.0%); pasteurization (80°C without air); homogenization (at 60°C); cooling down to 30-45°С; fermentation (5% fermentation); ripening in tanks (from 1.5 to 12 hours); cooling and maturation; definition of quality.

Ryazhenka is prepared from a mixture of milk and cream 6% fat. The mixture is subjected to languishing, i.e., pasteurization at a temperature of 95 ° C with an exposure of 3-5 hours. Then the milk is fermented with pure cultures of thermophilic streptococcus.

Varenets is made from baked milk, which is fermented with pure cultures of thermophilic streptococcus. A pleasant taste of Varenets is given by pieces of milk foams located on its surface.

Yoghurt is prepared from milk or a mixture of milk and cream, which is pasteurized at 60-70°C for 30 minutes, and then cooled to 45°C and leaven is added in the amount of 2-3%. The sourdough consists of pure cultures of thermophilic streptococcus and Bulgarian bacillus (50:50). Fermented milk is poured into a fermentation container. To prevent the yogurt from becoming too sour, it is quickly cooled after active fermentation.

Acidophilic fermented milk products (acidophilus, acidophilic milk, acidophilic yeast milk, acidophilic yogurt and acidophilic paste). A mandatory component of all these products is acidophilus bacillus, which is resistant to many antibiotics used for treatment. Acidophilic milk is also used to feed young farm animals in order to prevent and treat diseases of the digestive system.

Kefir prepared from pasteurized at a temperature of 80°C and cooled to 22-26°C milk. 5% starter is added to milk, fermented for 12 hours with kefir fungus, which causes various changes in milk: lactic acid bacilli and lactic acid streptococci cause lactic acid fermentation, and yeast - alcohol. Then they are bottled and sold to the distribution network. It is undesirable to store kefir for more than three days, since with an extension of the shelf life it acquires a strongly acidic taste.

Sour cream is produced with different fat content - from 10% (dietary) to 40% (amateur). When preparing sour cream, the cream is pasteurized at 80°C, cooled to 18-22°C, 5% starter is added (fermentation mode is 5-8 hours at a temperature of 18-22°C), cooled to 8-10°C (maturing occurs during days). The consistency of ripened sour cream becomes thick due to hardening and crystallization of fat and swelling of proteins.

The production of fermented milk dietary products - kefir, acidophilus, acidophilus milk, acidophilic yeast milk, Snezhok, Yuzhny drinks, yogurt and others - has increased tenfold.

Kefir is the most popular among the population, so it has taken a dominant position in the production of fermented milk drinks produced in Russia.

The birthplace of kefir is the North Caucasus, where for a long time it was made in wineskins or in wooden tubs. The technology of its production in the villages is simple - kefir fungi are poured with fresh milk, cooled to 18-20 "C, during the fermentation and ripening process, the product is periodically shaken. When kefir ripens, due to increased aeration, yeast actively develops, which affects the taste and consistency of the product: the consistency becomes liquid, creamy, taste-specific, sour, becomes sharp.

In Russia, kefir was produced as early as 1866-1867. in an artisanal way on fungi brought from the Caucasus in a dry form. Kefir fungi were revived in boiled chilled skim milk and used to make starter cultures. Milk for kefir was heated up to 16-23°C and fermented with starter directly drained from fungi. After obtaining a clot, the bottles were shaken to speed up the process of forming a drink and kept indoors at a temperature of 14-16 ° C for a day, and sometimes for a longer time.

The same technology was used to produce kefir at city dairies, while pasteurization of milk and bottling of the drink into bottles with hermetic seals were used. As a result of the length of the technological process, the laboriousness of many operations, the production of kefir was limited and the demand from the population for it was not satisfied, so the technology of kefir was changed: they began to produce it, in an accelerated way, which later received the name thermostatic.

Milk used for the production of kefir began to be fermented at high temperatures in thermostats without shaking and the corresponding accumulation of yeast fermentation products. As a result of a change in technology, instead of a soft but consistency of a semi-liquid drink with a characteristic refreshing taste, the factories began to produce a product with a dense clot, similar in taste to yogurt.

As a result of a number of research works, VNIMI has developed a reservoir method for the production of kefir, which is currently a generally recognized progressive method that is being widely introduced into the dairy industry.

The main stages of the technological process are the following:

heat treatment and homogenization of milk used for the production of kefir;

fermentation of milk, cooling and maturation of kefir in tanks;

bottling of high-viscosity drink into paper bags and glass bottles.

In the production of kefir by the tank method, milk is pasteurized at 85 ° C and kept. As the pasteurization temperature increases, the holding time decreases. An obligatory operation is the homogenization of milk: it prevents whey sludge in the finished product and gives it a homogeneous creamy consistency. Milk is homogenized under a pressure of at least 125 atm, the optimum homogenization pressure is 175 atm. Milk is fermented at a temperature of 20-25°C in double-walled tanks-reservoirs1 specially designed for the production of sour-milk drinks. The starter is introduced in a stream or in any other way with continuous mixing of the milk in the tank. The end of fermentation is determined when the acidity of the clot reaches 85-90 ° T. Water at a temperature of 1-3 ° C is supplied to the interwall space of the tank to cool the clot to the maturation temperature, and then turn on the stirrer to stir it and leave it alone for maturation.

In the process of maturation, kefir acquires a specific taste, different from the taste inherent in curdled milk.

The method of cooling depends on the scheme of the technological process adopted at this enterprise.

In the production of kefir, mixing and cooling it when serving for bottling is of great importance. The stirrer should not shake, and not cut it into layers and cubes, but smoothly and evenly mix the entire mass of kefir. Partial agitation or cutting of the curd results in whey separating (syneresis), just as churning kefir with a stirrer results in foaming, resulting in whey sludge. To preserve the quality of kefir, you should not use pumps that foam kefir and break the product. Chilled kefir is packaged in small containers (bottles and paper bags). Before being released into the distribution network, the finished product is cooled in the chamber to 6-8 ° C.

Below is the main technological scheme for the production of fermented milk drinks by the tank method (in two versions - with cooling in tanks and cooling in the flow on a plate heat exchanger), developed by VNPLSH and providing for mechanization and automation of main and auxiliary operations.

According to this scheme, milk is pumped through pipes, and the packaged finished product is transported internally (chain and belt conveyors, etc.).

In heat exchangers, milk and drinks are subjected to heat treatment (heating and cooling) to a predetermined temperature. Milk is purified from mechanical impurities in inline separators and processed in homogenizers to obtain the appropriate dispersion of fat and improve the viscosity of the drink.

Rice. 1. The main technological scheme for the production of fermented milk drinks by the tank method (first option):

1 - milk storage tank; 2 - centrifugal pump for pumping sour milk; 3- balancing tank; 4-centrifugal pump; 5-high temperature heat exchanger; 6 - remote control; 7 - separator-milk cleaner; 8 - bypass valve; 9 - homogenizer; 10- holding pasteurized milk; 11 - sourdough mixer; 12-pump for supplying sourdough; 13 - double-walled tank for fermented milk drinks

The beverage in the tank is agitated by a powered agitator. The drink is packaged in bottles or paper bags on filling machines and automatic machines. Labour-intensive processes of washing equipment are carried out with the help of irrigation and jet devices.

Control of the technological process and its management are automated.

On fig. 1 shows the main technological scheme for the production of fermented milk drinks by the tank method using tanks as coolers.

Raw milk, cooled to 4-6 ° C, is fed from the milk storage tank 1 by a centrifugal pump 2 to the balancing tank 3 of the pasteurization-cooling unit 5, then (under pressure) the pump 4 is sent to the regeneration section of the pasteurizer 5, heated to 55-60 C and goes to the milk purifier 7. The purified milk enters the homogenizer 9, where it is processed at a pressure of 125-175 atm, and returns to the pasteurization section of the heat exchanger 5, then through the bypass valve it is sent to holding at the pasteurization temperature and kept in vessel 10. After holding, the milk is returned to the regeneration section of the heat exchanger to transfer heat to the oncoming flow of raw milk. Milk at a temperature of 23-25°C enters from the heat exchanger into a double-walled tank 13, mixing along the way with the starter flow in the mixer 11. The fermented milk in the tank 13, having reached an acidity of 85-90° T, is mixed with a drive mixer, then cooled with ice water supplied into the jacket of the tank, to a predetermined temperature, after which it is packaged in glass bottles or paper bags.

The peculiarity of this scheme lies in the fact that after fermentation and reaching the desired acidity, kefir is mixed and cooled in the same tank, after which it enters the bottling and is fed into the chamber for post-cooling.

The process of cooling a fermented fermented milk drink in a double-walled tank lasts 3.5-6 hours. In the production of fermented milk products on thermophilic cultures, acidity rises very quickly. To stop the rapid increase in acidity after reaching 85-90 ° T, the product is fed from the tank to a plate cooler with the help of a low-speed pump, where the duration of the cooling process is reduced to 1 hour.

Another variant of the basic scheme of the technological process for the production of fermented milk drinks by the tank method with in-line cooling is shown in Fig. 2.

A feature of this technological mode is that milk is fermented in a double-walled tank or in a conventional milk storage tank 13 equipped with driven tubular "mixers", and when the acidity reaches 85-90 ° T, the drink is fed to the cooler 15 using a low-speed pump 14 from the tank 13. Drink cools very quickly in a thin layer.Then it enters the intermediate tank 16, and then goes by gravity to machines such as "Yudek", OR-6U, I2-ORK-6, I2-ORK-3 for packaging in glass bottles or to an automatic machine of the type AP-1N, AP-2N for packaging in paper bags.The packaged drink is transported by a conveyor to the storage room for further cooling.

The advantages of the production of fermented milk drinks by the tank method are as follows:

manual labor is almost completely eliminated as a result of mechanization and automation of the technological process;

increasing the qualifications of workers serving the line; Reduce labor costs and increase productivity

the cost of 1 ton of product is reduced by 4 r. 46 k.; production areas are reduced, since the finished product matures and cools in the same tanks in which it is prepared, and not in thermostatic rooms; reduced heat and cold consumption.

Rice. 2. The main technological scheme for the production of fermented milk drinks by a tank method with in-line cooling (second option):

1-reservoir for storage of milk; 2 - centrifugal pump for pumping milk; 3 - balancing tank; 4- centrifugal pump: 5-high temperature heat exchanger; b - remote control; 7-separator-milk cleaner; ; - bypass valve; 9 - homogenizer; 10- holding pasteurized milk; 11- pump for supplying sourdough; 12- sourdough mixer; 13 - tank for milk fermentation; 14-slow-speed pump for pumping kefir; 15 - plate cooler; 16 - intermediate tank for maturation of kefir.

The practice of operating equipment for the tank method of obtaining drinks has shown that lines assembled from machines and apparatus specially designed for the tank method for the production of fermented milk drinks are cost-effective in operation and ensure the production of high quality products.

If equipment for the production of drinking milk is used in the lines for the production of fermented milk drinks in a tank way, then it works intermittently.

At present, all the main machines and devices for completing a standard line are mass-produced (heat exchangers of the OPL-5 and OPL-10 types, A1-OGM homogenizers, automatic machines AP-1N, AP-2N, double-walled tank tanks and filling lines I2-OL2- 6 and I2-OL2-3. The line for the production of fermented milk drinks, completed from double-walled tanks, is universal, since it can produce drinks according to two options for the technological scheme after adding a pump and a plate pasteurizer to it.

The technological scheme for the manufacture of fermented milk products consists of the following operations: preparation of raw materials (milk or cream), normalization for fat, heat treatment, homogenization, cooling to the fermentation temperature, fermentation, fermentation, cooling (to a temperature not higher than 8 ° C).

The production of kefir and sour cream has its own characteristics.

Depending on the conditions of fermentation, there are thermostatic and reservoir methods of production. With the thermostatic method, fermented milk or cream is poured into bottles or jars, which are then placed in thermostatic chambers, where the fermentation process takes place. The next operations are cooling in a cold chamber and ripening of kefir and sour cream, i.e. keeping the products at a low positive temperature.

With the tank method of production, fermentation, cooling and maturation are carried out in large containers (double-walled tanks), and then ready-to-sell kefir is bottled or packaged, sour cream is placed in large containers (bidong, barrels).

Features of the manufacture of cottage cheese are that the fermentation process can proceed not only as a result of the vital activity of the starter microorganisms, but also under the action of rennet (a powder obtained from the mucous membrane of the fourth compartment of the stomach - the abomasum of dairy calves and lambs) introduced into milk. In addition, after fermentation, whey is separated from the clot.

The quality of fermented milk products depends on the composition and properties of raw materials, the type and activity of starter cultures, and technological modes.

So, with a reduced content of vitamins in milk, free

amino acids and trace elements that are necessary for reproduction

lactic acid bacteria, the process of fermentation of milk proceeds slowly. In the spring, milk lacks these elements.

Lactic acid bacteria develop poorly, and the ability of rennet to coagulate in old milk, in milk obtained from cows with mastitis, is reduced. Milk coagulates poorly with rennet if the content of proteins and calcium salts in it is lowered. Defects in milk in terms of organoleptic characteristics will also appear in fermented milk products.

The taste, smell and texture of fermented milk products depend on the composition of the starter culture. Vigorous acid-forming agents (mesophilic and thermophilic lactic streptococcus, Bulgarian bacillus) cause significant accumulation of lactic acid and obtaining a dense clot with intensive whey separation, weak acid-forming agents (aroma-forming streptococci) - a delicate clot with a pleasant taste and aroma. Creamy streptococcus, acidophilus bacillus contribute to an increase in the viscosity and elasticity of the product, and prevent the separation of whey. Yeast, aroma-forming and acetic acid bacteria, releasing carbon dioxide in the process of their development, destroy the clot.

The heat treatment of raw materials, which is necessary to destroy foreign microflora and inactivate enzymes, affects the strength of the clot and the intensity of whey separation. With an increase in the pasteurization temperature of milk, the strength of the clot increases and the intensity of whey separation decreases.

In the production of sour-milk drinks and sour cream, high pasteurization temperatures are recommended for milk (85-87 ° C with an exposure of 5-10 minutes or 90-92 ° C with an exposure of 2-3 minutes) and cream (85-95 ° C with an exposure of 15- 20 s).

In the production of cottage cheese, in order to better separate whey and reduce protein losses, it is advisable to pasteurize milk at 78-80 ° C with or without holding for 20-30 seconds.

Homogenization of milk and cream (in the production of kefir, curdled milk, sour cream) accelerates the formation of a clot, increases its viscosity and plasticity, and reduces the release of whey. In the production of cottage cheese, it is impractical to homogenize milk, since the clot is flabby, poorly releasing whey.

In milk or cream having a temperature favorable for the development of microorganisms, leaven is added in the amount of 3-5%.

The temperature regime and the duration of fermentation depend on the microflora that is part of the starter cultures. When using mesophilic types of lactic acid bacteria, the fermentation temperature is 28-32 ° C and the duration is 5-7 hours, thermophilic - 40-45 ° C for 2.5-4 hours, kefir culture - at a temperature of 20-25 ° C for 8- 12 noon

The end of fermentation is determined by the strength of the clot and titratable acidity. For drinks, it should be 75-85 °T, for sour cream - 65-70, cottage cheese of various fat content - 60-85 °T. The consistency, taste and smell of products are formed during this technological process.

To stop lactic fermentation, fermented milk products are cooled and stored at a temperature not exceeding 8°C.

Kefir, koumiss and other products of mixed fermentation before cooling are subjected to maturation for the development of yeast and aroma-forming bacteria (kefir is kept at a temperature of 14-16°C for 6-12 hours, koumiss - at 16-18°C).

Sour cream is also ripened. At the same time, the structure and consistency of the product are finally formed. Sour cream is cooled to a temperature of 1-6°C and kept. Cooling and ripening lasts 6--48 hours depending on; sour cream packages. In the process of maturation, crystallization and hardening of milk fat occurs, which increases the strength of the structure and viscosity of sour cream, as well as the absorption of moisture by casein and whey proteins, which also improves the consistency of the product.

When curd is produced, the separation of whey from the clot begins at an acidity corresponding to the isoelectric point of casein (i.e., pH 4.6-4.7) for an acid clot and at a pH of 4.7-5.0 for acid-rennet. The process of syneresis is accelerated by cutting the clot and heating it to a temperature of 30-36 °C.

Whey is easier to separate with the acid-rennet method of manufacture. This method is used in the production of fatty cottage cheese. At the same time, the clot is not heated and the loss of fat with whey is insignificant. Milk fat makes it difficult to release moisture from the clot, so whey separation is easier to control in a fat-free clot. The acid method is more often used in the production of low-fat cottage cheese.

Thus, summing up all of the above, it can be noted that the technological processes for the production of fermented milk products are very diverse, but all of them must comply with production standards so that buyers receive a quality product, and, accordingly, its producers receive high profits.