pasteurization technology. How is pasteurized milk made?

Pasteurization is understood as a one-time process of heating products that have a liquid consistency. The technology is named after Louis Pasteur (1822-1892), a French microbiologist who proposed to disinfect beer and wine in this way by destroying unwanted microorganisms from the composition of drinks. In the future, this method gained great popularity and began to be used to disinfect products and increase their shelf life.

Milk pasteurization process

The process of pasteurization of milk affects the microorganisms contained in its composition, depending on the degree of heat treatment and the duration of heating. The process of pasteurization of products differs from the sterilization process in that in the first case only the destruction of microbes occurs, and in the second - spores. Pasteurization does not involve boiling, which eliminates absolutely all milk microflora, but cleans the product of pathogens (for example, tuberculosis or brucellosis bacteria) at a temperature slightly lower than the boiling point. At the same time, the main properties of milk (consistency, taste, smell) remain practically unchanged.

It is possible to achieve complete (99%) destruction of microorganisms by ensuring the sterility of dishes, equipment and equipment used for pasteurization of bulk milk. If contaminated milk is allowed to enter already pasteurized milk, spoilage of the entire amount of the product should be expected. Poorly sterilized equipment used for milk pasteurization can contain up to 1 billion bacteria, which, actively multiplying, are capable of increasing the number of pathogenic microbes in the total mass of the product up to 1 million/ml in a fairly short period of time.

Pasteurization is considered to be the least expensive and affordable way to disinfect the resulting milk for further consumption or production of various dairy products based on it. The use of pasteurized milk guarantees the high quality of finished products, prevents their sourness caused by butyric bacteria and the occurrence of undesirable processes associated with the active reproduction of Escherichia coli or other microorganisms.

The microflora of livestock kept on pastures can be destroyed as much as possible by pasteurizing it. When receiving milk from stall animals, there is a high probability that bacteria of manure particles get into the product, resistant even to high temperatures. On the contrary, in the milk collected from pasture cattle, plant bacteria are found mainly. This fact determines the mandatory procedure for cleaning milk before placing it in pasteurizers.

Pasteurization methods

There are 3 types of pasteurization:

This method is called long-term pasteurization. Milk must be heated to a temperature of 63-65 ° C and pasteurized for half an hour;

This method, otherwise known as short-term pasteurization, involves heating the product to a temperature of 72-75°C. After 15-20 seconds heat treatment should be stopped;

With instant pasteurization, milk should be brought to a temperature of 85-90 ° C without subsequent exposure.

Heat treatment (at 80-85°C) changes the taste and aroma of milk. Subjected to temperature influence, some elements contained in milk change their physical and chemical properties, and, accordingly, the composition of the product changes slightly.

For example, the gases that make up milk evaporate, the acidity of the product decreases somewhat (by 0.5-1 °T), changes also affect the salt composition (phosphate salts become insoluble). Heaters used in the manufacture of pasteurized milk may be covered with burn deposits due to the deposition of milkstone. Calcium salts slow down the clotting of milk, which requires the addition of an artificial solution of calcium chloride. With the flash pasteurization method (when the temperature is above 85°C), the casein begins to change. And protein albumin tends to denature already at 60-65°C. Vitamins are the most resistant to heat treatment, especially when oxygen access to the pasteurizer is limited.

Experts do not recommend boiling pasteurized milk, as this changes the composition of milk, reducing the content of nutrients and vitamins A and C. You can pasteurize milk at home in a water bath. When water is heated in a saucepan to 63-65 ° C, the fire must be turned off, the milk must be kept for 20-30 minutes, and then cooled by placing in cold water. In the process of heating, it is necessary to constantly stir the milk.

Mankind has always tried to be able to correctly extend the period of use of products, without reducing its useful properties. In the middle of the 19th century, the great scientist, the founder of immunology, Louis Pasteur, discovered the technology of pasteurization, which made it possible to disinfect food and significantly increase their shelf life.

In today's world, most liquid products go through this process. The word "pasteurized" most often we see in the store on the packaging of milk. And it becomes interesting, is it possible to pasteurize milk at home? Certainly yes. So let's try to understand this process in detail.

Pasteurization - what is it?

First, let's talk about the pasteurization process itself. This technology involves heating milk to a 60-degree temperature for half an hour or up to 80 degrees, but here the heating time is reduced to 10-20 minutes. This means that the pasteurization temperature of milk is 60-80 degrees, depending on the duration. During this period, some of the microorganisms die, and the other part reduces activity, thereby extending the shelf life of the dairy product. As a result, we get pasteurized milk. Pasteurizing milk is a simple process.

Pasteurization at home

Now about how pasteurization of milk is carried out at home. As an example, let's talk about long-term pasteurization at a temperature of 60 degrees. The most optimal would be to heat not the milk itself, but a pot of water, and place a package of milk there. With this mode of pasteurization, the milk will be pasteurized in the same way as if we boiled it, but the quality of the dairy product will undergo minimal changes.

Do not forget the most important thing: milk pasteurization is a one-time process. From the second time, milk will not get better, but will only lose some of its beneficial properties. We also advise you, if you have your own cow, to cool down after receiving fresh milk. After all, it is known that at its temperature, such milk begins to turn sour after two or three hours. Pasteurizing and cooling milk to the right temperature will help keep it fresh longer. Refrigerate milk to 10 degrees to prolong its shelf life.

Pasteurization of milk in a slow cooker

With the advent of the era of multicookers, a new version of milk pasteurization came to the kitchen. Now you do not need to stand all the time at the stove and look at the clock, afraid that the milk will run away at any moment, and even at the same time constantly remove the foam from it. Now just pressing a couple of buttons. In order to pasteurize milk in any slow cooker, you need to pour it into a saucepan and set it to a temperature of 60 to 80 degrees. If the milk is homemade, then at a temperature of 80 degrees, you can set a timer for 20 minutes. If it is purchased, then it would be better to increase the pasteurization period for greater reliability by another twenty minutes.

The new generation of multicookers has a "Pasteurization" mode. There it is already enough just to pour milk into the pan, press one button and just wait for the notification about the completion of this process. It is also advisable to sterilize jars or bottles where you will then drain the milk.

pasteurization mode. Is there a difference?

As mentioned above, the procedure time depends on the selected temperature. And depending on these two factors, the following types of pasteurization are distinguished: ultra-high temperature, high-temperature short-term and long-term. Long-term pasteurization is a process that lasts thirty minutes at a temperature of 60 degrees. This type is considered the most time-consuming, but also the most reliable in terms of the destruction of harmful microorganisms.

Short-term high-temperature pasteurization is carried out only in industrial conditions, since this mode requires special equipment in which milk is heated for several seconds, after which it is immediately cooled. The downside of this pasteurization is that if you make a mistake just for a couple of seconds, then you can either carry out the pasteurization not to the end, as a result of which all microorganisms will survive, or overexpose the milk, thereby destroying all its useful properties. Therefore, it cannot be said that pasteurized purchased milk from any enterprise will be of the same quality.

Instant heating

There is also a fairly simple pasteurization method called flash heat. This process was developed for mothers who are HIV positive and cannot safely breastfeed their babies. The method is that you first need to make a water bath. A water bath is done quickly and easily. We take two pots of different sizes. Pour water into a larger saucepan and set it to heat on the stove, after which we put a smaller saucepan into a large one. After that, pour the milk into a small saucepan, and as soon as the water boils, immediately remove the milk, ready for use and past a brief pasteurization process

To drink or not to drink?

Many opponents of this process say that all beneficial bacteria are destroyed, and there is no point in drinking milk after pasteurization, because this method was created only in order to extend the shelf life of milk. But they confuse it with the sterilization process, where the milk is heated to 100 degrees, and in this mode all bacteria are destroyed, leaving just a white shell. During pasteurization, the maximum temperature is only 87 degrees, which means that milk retains most of its beneficial properties. Therefore, now, wondering whether it is worth pasteurizing milk, you can decide on the answer.

Pasteurization is a method of disinfecting organic liquids by heating them to a temperature below 100 °, when only vegetative forms of microorganisms die. Pasteurization is widely used, the quality and organoleptic properties of which are significantly reduced when heated above 100 ° (for example, pasteurization of milk, cream, fruit, and other, mainly liquid, food products). At the same time, the products are freed from non-spore-bearing pathogenic microorganisms, yeasts, mold fungi (microbial contamination is reduced by 99-99.5%). Pasteurized products almost completely retain their nutritional and taste properties.

In the dairy industry, three methods of pasteurization are used: long-term (30 minutes at 65°), short-term (15-20 seconds at 72-75°), instant, or high (heating up to 85-90° without exposure). for the correct conduct of pasteurization, monitoring its effectiveness are important measures to prevent diseases associated with the consumption of milk. In bacteriological laboratories, pasteurization is used to process proteins by repeated (2-3 days in a row) heating to 55-60 ° for 30-60 minutes.

Pasteurization is a method of neutralizing organic liquids by heating them to t ° below 100 °, when only vegetative forms of microbes die. Pasteurization is applied to materials whose quality is significantly reduced when heated to 100 ° and above.

Pasteurization is widely used to preserve milk, cream, fruit, fruit and berry juices, jelly and other products for 20-30 minutes.

Pasteurization causes a slight change in the physico-chemical properties of milk. During pasteurization, pathogens of infectious diseases, yeast cells, mold fungi die in milk, and enzymes are also destroyed (see table). In the process of single pasteurization, a decrease in the total microflora is achieved (by 99-99.5%). After a single pasteurization, spore sticks remain in milk; a significant percentage of the residual microflora are micrococci and lactic acid bacteria, thermophilic streptococci and rods.

In the dairy industry, three methods of pasteurization are used: long-term pasteurization at 65 ° with keeping the product in tanks or baths for 30 minutes; short-term at 72-75° with holding for 15-20 seconds; instant, or high, pasteurization when heated to 85-90 ° without aging.

In bacteriological laboratories, pasteurization is used to sterilize protein culture media by reheating to 55-60°C, i.e. below the protein coagulation temperature, for 60 or 30 minutes. 2-3 days in a row. If necessary, the process is repeated up to 4 times.

Pasteurization is a mandatory technological operation in the production of dairy products.

Purpose of pasteurization:

1. Destruction of pathogenic microflora, obtaining a product that is safe for the consumer in terms of sanitary and hygienic terms.

2. Reducing the overall bacterial contamination, the destruction of raw milk enzymes that cause spoilage of pasteurized milk, reducing its storage stability.

3. A directed change in the physicochemical properties of milk to obtain the desired properties of the finished product, in particular, organoleptic properties, viscosity, clot density, etc.

The main criteria for the reliability of pasteurization is the mode of heat treatment, which ensures the death of the most resistant of pathogenic microorganisms - tubercle bacillus. It has been established that the destruction of the phosphatase enzyme in milk occurs after the death of non-spore-forming pathogenic bacteria. For example, at a temperature of 75 ° C, the causative agent of tuberculosis dies after 10-12 seconds, and phosphatase at this temperature is destroyed only after 23 seconds. Hence, an indirect indicator of the effectiveness of pasteurization is the destruction of the phosphatase enzyme in milk, which has a temperature optimum slightly higher than that of a tubercle bacillus.

The pasteurization efficiency as a percentage is expressed as the ratio of the number of cells destroyed to the content of bacterial cells in raw milk. With the correct conduct of the pasteurization process, the efficiency reaches 99.99%.

Milk pasteurization modes

At the enterprises of the dairy industry, the following pasteurization modes are used.

1. Long-term pasteurization is carried out at a temperature of 63-65 ° C with an exposure of 30 minutes (equipment - long-term pasteurization baths, universal tanks). Disadvantages: long process, all microflora is not killed.

2. Short-term pasteurization is carried out at a temperature of (76 ± 2) ° С with a holding time of 20 seconds (equipment - plate pasteurization and cooling installations). Advantages: the process takes place in a stream without air access, vitamins are preserved.

3. Instant pasteurization is carried out at a temperature of 85-87°C without exposure (equipment - tubular pasteurizers). The disadvantage is the lack of a regeneration section.

When choosing production modes of pasteurization, along with the need to suppress microflora, the features of the technology of a particular dairy product are also taken into account. So, in the manufacture of rennet cheeses, the pasteurization temperature is set within 72-76 ° C, so as not to cause denaturation and the transition of whey proteins into the cheese mass. In the production of fermented milk products, on the contrary, the pasteurization temperature is increased to 95 °C in order to exert a thermal effect on the milk protein system in order to ensure a good consistency of fermented milk products.

The resistance of microorganisms to heat treatment increases with an increase in the content of fat and solids in products (cream, ice cream mixture), since fatty and protein substances have a protective effect on microbial cells. Therefore, for products with a high content of fat and solids, the pasteurization temperature should be increased by 10-15% compared to the pasteurization temperature of milk. An elevated temperature during pasteurization of cream used for butter production is necessary for the complete destruction of enzymes (lipases, proteases, etc.) that cause butter spoilage.

After the pasteurization process, as a result of which the microflora is inactivated to the required extent, the milk is most often subjected to cooling. This is done for the following reasons:

In milk, simultaneously with bacteria, when heated, the natural antibacterial system is destroyed;

Milk must be protected from damage by secondary microflora, which over time adapts to the operating conditions of pasteurization equipment and develops in places difficult for mechanized washing and disinfection (under rubber gaskets);

Milk must be protected from the risk of reproduction in it of pathogenic forms of microorganisms that can get into milk after pasteurization through the air, hands of attendants, poorly washed parts of the equipment.

Factors Affecting Pasteurization Efficiency

The main factors influencing the efficiency of pasteurization are the heating temperature and the time of its exposure to milk.

Numerous studies have established the dependence of the holding time (z) on the pasteurization temperature (t).

lnz = 36.84 - 0.48t (16)

The pasteurization modes determined by this equation guarantee the deactivation of tuberculosis and E. coli. Knowing the pasteurization temperature, the time is determined from this equation. The data is presented below.

Heat treatment or pasteurization is the process of heating milk from 63 ° C to a temperature close to the boiling point. This process takes its name from the famous French scientist Louis Pasteur (1822-1892), who first used this method to kill microorganisms in wine and beer.
The effect of pasteurization on microorganisms contained in milk depends on the temperature to which the milk is heated and the length of exposure at that temperature. Pasteurization destroys microbes, and sterilization (heating milk above the boiling point) destroys spores at the same time. Boiling destroys the entire microflora of milk, with the exception of spores that are resistant to boiling temperature. Pasteurization without a noticeable change in the organoleptic properties of milk (taste, smell and texture) destroys tuberculosis, brucellosis and other pathogenic bacteria. In ordinary skimmed milk, 99% of bacteria die only if the equipment, inventory, and utensils used in the pasteurization process are well and reliably sterilized. Thus, the addition of contaminated milk containing 1 billion bacteria to pasteurized milk (that is, such an amount that can be left unattended in the dairy inventory) will increase the number of bacteria in milk to 1 million in 1 ml. These bacteria will actively multiply and will inevitably lead to spoilage of all milk. Pasteurization is therefore the simplest and cheapest way to disinfect milk. Milk is also pasteurized during the production of all dairy products in order to protect them subsequently from undesirable processes that are caused by the vital activity of bacteria and especially E. coli, butyric bacteria, etc. When cattle are kept on pasture, the microflora of milk is destroyed by heating more completely than when kept in a stall. This is explained by the fact that during stall keeping, bacteria enter the milk mainly from manure particles. These bacteria are more resistant to heat in their properties. With pasture content in milk, mainly bacteria that multiply on plants are found. Milk must be thoroughly cleaned before pasteurization. In practice, three modes of pasteurization are used: during long-term pasteurization, milk is heated to 63-65 ° C and kept at this temperature for 30 minutes; short-term pasteurization is carried out at 72-75 ° C with exposure for 15-20 s, which is carried out in a stream; instant pasteurization - heating milk to a temperature of 85-90 ° C without exposure. Thermal action on milk leads to some changes in its constituent substances. When heated, the gases dissolved in it evaporate from the milk. Due to the removal of carbon dioxide, the acidity of milk decreases by 0.5-1 °T. At temperatures above 85 ° casein is partially changed. But milk albumin is most affected: at 60-65 ° C, it begins to denature. Violated during pasteurization and the salt composition of milk. Soluble phosphate salts become insoluble. From the partial coagulation of proteins and the formation of insoluble salts on the surface of heating devices (pasteurizers), sediment-milk stone (burnt) is deposited. Pasteurized milk coagulates more slowly with rennet. This is due to the precipitation of calcium salts. Adding a solution of calcium chloride to such milk restores its ability to coagulate. Vitamins are resistant to high temperatures, especially if the milk is heated without oxygen from the air. Heating to high temperatures (80-85°) gives the milk a special flavor and aroma, which intensifies as the temperature rises. When boiled, the composition of milk also changes. For example, the content of vitamins A and C decreases almost 2 times. Nutrients are lost in the range from 15 to 20% due to the formation of precipitation of proteins, fat and calcium salts on the walls of dishes. Therefore, boil pasteurized milk without special need should not be.
At home, you can also recommend long-term pasteurization of milk, which is performed without much difficulty. It is made through heated water. Milk poured into a saucepan is stirred with a clean spoon while heating. As soon as the temperature rises to 63-65 ° C, heating should be stopped and kept for 20-30 minutes. After that, the pan with milk is placed in cold water.