The dairy industry includes a large number of individual sectors: whole milk production, buttermaking, cheese making, the production of canned condensed and dried dairy products, ice cream, the production of baby food, whole milk substitutes, etc. Each of these industries has its own characteristics, but they are all more or less related to milk processing.
Industrial processing of milk is a rather complex set of interconnected chemical, physico-chemical, microbiological, biochemical, biotechnological, thermophysical and other technological processes that differ depending on what kind of product we are talking about.
For example, in the manufacture of drinking milk and dairy products, all components of milk are used. In the production of sour cream, cream, sour milk cheese, butter, hard cheese, the processing of individual components of milk is carried out. The production of canned milk is directly related to the preservation of all milk solids after extracting moisture from it.
Yogurt is a fermented milk product that is produced on the basis of pasteurized milk, normalized by mass fraction of fat and solids, with or without sugar, flavorings, fruit and berry fillers, thickeners, stabilizer, vegetable protein and other ingredients. In appearance, yogurt is a homogeneous creamy mass with a broken or undisturbed (depending on the production method) clot, and in fruit and berry products - with the addition of pieces of berries and fruits. The color of ordinary yogurt is milky, and for yogurts with fillers, it is determined by the syrups added to it.
There are two main methods for producing yogurt - tank and thermostatic. At the same time, fruit and berry yogurts are produced only in a thermostatic way. The technological process for the production of yogurt in a reservoir way consists of several basic operations: acceptance and preparation of raw materials, normalization of milk for fat and solids, purification, homogenization of the mixture, pasteurization, cooling, fermentation, the introduction of fillers and dyes, fermentation, mixing, cooling, bottling, packaging marking.
The main raw materials used for the production of yogurt must be of very high quality. It should contain a minimum amount of impurities and bacteria that can interfere with the development of yogurt bacteria. For this reason, the requirements for the raw materials used are very high. Manufacturers have to spend a lot of time looking for trusted suppliers and conduct thorough checks of each new batch of raw materials before using it to produce their products. Raw milk, selected by quality, preliminarily passes through several technological processing steps. It is normalized by the mass fraction of fat or solids.
First, the normalization of the solids contained in it is carried out. The most common way to normalize the composition of dry substances is the evaporation of pasteurized and homogenized milk at a temperature of 55-60 degrees Celsius. In this case, from 10 to 20% of the liquid (from the total volume of milk) is removed from the raw material. Also, to normalize the solids content, skimmed milk powder (approximately 3% of the weight per total volume) can be added to the milk, which is restored in accordance with the accepted regulatory documentation, or concentrated milk.
Depending on the type of yogurt produced, the fat content in it may vary. According to this parameter, the milk that is used to make yogurt is normalized in the range from 0.1 to 3.5%. Moreover, the lower the fat content in the feedstock, the more difficult it will be to process a yogurt clot. For this reason, manufacturers are trying to increase the solids content in the manufacture of low-fat yogurt. In fat, milk is normalized in two ways - by adding whole milk or cream to skim milk, as well as in a stream using a separator-normalizer.
Particular attention is paid to the air content in milk. In order for the finished product to have a longer shelf life, have a higher viscosity, no odors, and also to reduce the time of its fermentation, the air content in the raw materials should be minimal. For this, milk undergoes deaeration (air removal) in special vacuum chambers.
In the production of sweet yogurt, normalized milk is heated to a temperature of 40-45 degrees, sugar is added to it, which is previously dissolved in part of normalized milk at the same temperature in a ratio of 1 to 4. Then the mixture is cleaned on milk separators.
The next step in the production of yoghurts is the homogenization of raw materials, the purpose of which is to avoid cream settling during ripening and to ensure an even distribution of fat in milk. In order for the product that results in high quality, the milk is homogenized at a temperature of 65-75 degrees Celsius and at a pressure of 200-250 atmospheres. After that, stabilizers (carrageenin, gelatin, pectin, starch, etc.), aromatic and flavoring fillers are added to it.
Before the yeast is added to milk for the production of yogurt, it undergoes heat treatment (pasteurization), which allows you to prepare the basis for bacterial starter culture and reduces the risk of separation of whey in the finished product (resulting in a stable consistency of yogurt). For this, the milk is heated to a temperature of 90-96 degrees Celsius and maintained at this temperature for five minutes. For the manufacture of yoghurts, special starter cultures are used, which may include various types of bacteria. The most common of these are Bulgarian coli (Lactobacillus bulgaricus) and thermophilic streptococcus (Streptococcus thermophilus). However, some manufacturers may add other types of bacteria to the main starter culture (for example, Lactobacillus acidophilus or Bifidobacterium). Both Bulgarian bacillus and thermophilic streptococcus produce lactic acid, which is the final product of milk fermentation in an airless way. At the same time, thermophilic streptococcus is responsible for the production of acid, and Bulgarian stick gives a specific flavor to yogurt. Although these types of bacteria develop interconnectedly, the interaction between them is determined by the percentage of each of them in the leaven, the ambient temperature and the duration of ripening.
The amount of added starter culture is usually 3-5% of the volume of the fermented mixture, and the starter culture, which is prepared with sterilized milk, is 1-3%. Sourdough is added to milk in the tank for fermented milk products with the stirrer working. In addition, it can be added before milk is fed into the container. After filling the tank, the entire mixture is thoroughly mixed for 15 minutes. The end of the ripening process is determined by the formation of a strong clot with an acidity of 95-100 ° T. First, the clot is cooled for 10-30 minutes, and then mixed to achieve a uniform consistency and to avoid separation of serum.
Dairy enterprises do not produce yeast on their own, but acquire them in various forms. For example, they can be sublimated (used to propagate sourdough), concentrated sublimated (frozen cultures to propagate sourdough) and superconcentrated (which are added directly to the product).
After fermentation is added, milk is fermented using special equipment for fermentation. When using the reservoir method, the pressure difference between the incubation tanks and the packaging machine is of great importance. It should be minimal, so it is so important to take responsibility in choosing the type and size of pipes, pumps, coolers, valves and other equipment.
The almost finished product is cooled and then sent for final heat treatment in a starter plant at a temperature of about 60-80 degrees Celsius. The product is hot (heated to a temperature of 60 ° C, which guarantees a long shelf life) is packed in plastic bottles, cups (the most common packaging), cardboard bags. Filling cups and other containers with yogurt is carried out automatically. For special equipment, marriage sheets are supplied, which act as raw materials for the production of plastic cups. First, they are disinfected, and then with the help of a hot press, cups are formed from them, which are filled with yogurt. Packaging is done on trays with 24 cups each. The same packaging machine in two stages hermetically seals the filled cups with foil. Then the trays are folded onto carts and transported to a refrigerated container, where the product is cooled again in a short time, after which it is marked and sent for storage. Sometimes in warehouses, finished yogurt is 2-3 days. There it ripens, keeps track of the packages. At this time, in the laboratory during the production, studies of samples from the last batch are carried out.
The technological process for the production of yoghurts by the thermostatic method includes the following stages: acceptance and preparation of raw materials, normalization of raw materials for fat and solids, cleaning and homogenizing the mixture, pasteurization and cooling of the mixture, fermentation, bottling, packaging, labeling, souring and cooling. In this way, fruit and berry yogurts are produced. In fact, all the operations that are used with this method almost completely coincide with the stages of yogurt production by the reservoir method. At least until fruit and berry fillers are added to them. Fillers are added with constant stirring to the mixture, which is pre-cooled to the fermentation temperature. Then the whole mass is still mixed for 15 minutes. Fermentation is carried out in the same way as when using the reservoir method. The fermented mixture is poured into a glass container and sent to a thermostatic chamber with a constant temperature of 38-42 degrees for 3-4 hours, where the mass is ripened. After this, the clot is checked for strength and acidity, and the finished product is transported to the refrigerator for cooling to a temperature of 6 degrees. Such yogurts have a short shelf life - not more than 4 days from the date of manufacture at a temperature of 6 degrees Celsius.
Recently, in most modern factories, the reservoir method of producing yoghurts has been used, since the product prepared in this way, although it cannot be called completely natural, has a longer shelf life and sale. Modern equipment allows you to almost fully automate the production of yoghurts. To organize production, you will need a special production line, which includes the following equipment: a two-layer tank made of food-grade stainless steel with a frame-type mixing device, a milk pump, a cream separator, a normalizer, a buffer tank for cream, a two-layer tank with an anchor-type mixing device, a homogenizer, flow cooler, emulsifier with a mixing device, starter culture, filling apparatus, shutoff and pipe fittings, control panel.
Such a line can be used for the production of yoghurts with or without fruit preparation, with a long shelf-life and packaging in 150 and 200 ml cups with sealing on top with aluminum foil with the application of the production date and expiration dates. Its productivity is 12000-15000 cups per shift lasting about nine hours and 24000-30000 cups for two shifts lasting about nine hours each. The average energy consumption of such equipment is 20 kW per hour. Water consumption reaches 12 cubic meters. meters per day. To place the line, a production area of about 150-200 square meters will be needed. meters and area for warehouses for storage of finished products - 50-80 square meters. meters. The dimensions of the cold storage room should be about 6 by 2.5 meters. To work in a small production, you will need a dairy technician, one electrician and six skilled workers. About thirty people per shift work at a large enterprise in terms of production volumes. The average cost of equipment for the production of yogurt ranges from 2 million (2000 liters per day) to 4 million (4000 liters per day) rubles.
Although yogurt is an off-season product that should be in demand all twelve months, nevertheless, the time of the year has a certain effect on its sales level. In the summer, almost all manufacturers notice a significant decrease in their sales. This fact is explained by the fact that consumers try to buy less dairy products in the hot season, since there is a high risk of purchasing a spoiled product. Unfortunately, this is, indeed, a frequent occurrence, which is very difficult for small production enterprises to deal with. The main reason for the rapid deterioration of dairy products in the summer is the non-compliance with the conditions (temperature conditions) of their transportation and storage in retail chains.
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