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Milk pasteurization time. How is pasteurized milk made?

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.

Pasteurized milk - longer stored without loss of useful properties. Today, there are two different processes aimed at increasing the shelf life of a dairy product: pasteurization and ultra-pasteurization. The processes are similar, but they also have differences. Milk can be pasteurized using a special bath, conventional or infrared pasteurizer.

History of pasteurization

The French microbiologist Louis Pasteur is the founder of the pasteurization process. In the mid-eighties of the nineteenth century, winemakers turned to a famous scientist with a request to find a tool that could purify wine from harmful and destructive enzymes. The result of a number of experiments was the discovery - you can get rid of harmful microorganisms if you warm the wine to a temperature of 55 - 60 degrees. He applied a similar method to milk in order to purify it from the tubercle bacillus.

Pasteurization has taken root and has become popular in many countries around the world. It began to be used not only for disinfection, but also to increase the shelf life of a dairy product.

Types of pasteurization

Today pasteurization is divided into three types:

  1. Long (30-60 minutes, at a temperature of 64 degrees),
  2. Short (30-60 seconds, at a temperature of 86 -91 degrees),
  3. Instant (a few seconds, at a temperature of 98 degrees).

Pasteurization should be distinguished from sterilization. For sterilization, milk is brought to a temperature of 150 degrees and processed for half an hour.

Such a long heat treatment leads to the death of all microorganisms, and the shelf life of the sterilized product reaches up to a year. The absence of lactic bacteria in it leads to the fact that the milk does not sour, but begins to taste bitter. The disadvantage of sterilization is that the product loses its nutritional value.

Pasteurization efficiency

Pasteurization of milk consists in a single heating of the product for a certain time and to a certain temperature (depending on the type of pasteurization). The pasteurization process leads to the death of mesophilic bacteria, but lactic acid streptococci and enterococci retain their activity. During the subsequent storage of milk at a temperature of less than +8 degrees, bacteria reduce biological activity and do not impair the quality of the product.

Pasteurization of milk does not lead to the destruction of lactic acid sticks - they cease to develop only if the storage conditions are properly observed.

Psychrotrophic bacteria are less resistant to the pasteurization process, so only a small number of microorganisms remain in the finished product.

The efficiency of the process directly depends on the types and number of microorganisms contained in the original product. And storage conditions largely determine the effectiveness of pasteurization. If after milking the milk is immediately cooled to +3 degrees, then only psychrotrophic microorganisms survive and continue to multiply in it. They have a rather low thermal stability, so the pasteurization efficiency of such milk is 99.9%.

The development of psychrotrophs in the raw product leads to the production of heat-resistant proteases and lipases, which can worsen the taste of not only pasteurized milk, but also any dairy product.

Storing milk at temperatures above +9 degrees leads to the active reproduction of heat-resistant bacteria. The amount of their biomass can be more than half of all microorganisms found in milk. The pasteurization efficiency of such milk can be less than 97%.

UHT

This process is also a heat treatment of a dairy product to increase its shelf life. UHT milk can be drunk not boiled, and this is an undeniable advantage over the pasteurized counterpart. The boiling process leads to the destruction of all useful qualities, as well as the decomposition of proteins and a change in the absorption of calcium.

For ultra-pasteurization, special closed containers are used. The essence of the process is that milk is brought to a temperature of 133-153 degrees, maintained at this temperature for two to three seconds, and gradually cooled to 4-5 degrees. This type of treatment leads to the death of all microorganisms.

Ultra-pasteurized milk does not turn sour, but retains all the beneficial qualities, since the heat treatment process does not adversely affect the state of vitamins, basic lactic ferments and mineral salts.

UHT milk can be stored for up to two months in a closed package, even without a refrigerator, at a maximum room temperature of +25 degrees.

An open box can be stored for no more than five days. After five days, UHT milk begins to taste bitter and acquires an unpleasant odor.

Modern technologies make it possible to produce ultra-pasteurized milk, which is not inferior in its useful qualities to whole steam milk.

Milk pasteurizer

A pasteurizer is an equipment designed for heat treatment of a dairy product. There are a number of requirements for pasteurizers:

  • They must destroy all pathogenic bacteria,
  • Ability to handle a variety of products
  • Preserve the unique qualities of processed products,
  • Prevent product loss during processing,
  • Be made from materials approved for use in the food industry.

Pasteurizers are divided into several types according to their main characteristics. So, by design, they are divided into open and closed. And depending on the workflow, there can be periodic or continuous actions. In the dairy industry, permanent pasteurizers are more used, but for the production of any canned products, a batch pasteurizer is more often used.

Another difference is in the type of heat treatment. Some pasteurizers use sterile steam in the process. This method involves the subsequent cooling of milk in a special vacuum chamber. Others use a heat exchanger. In the built-in regeneration section of which a cooling process is provided.

The usual equipment of the pasteurizer includes:

  • working capacity,
  • Milk and water pumps,
  • heating system,
  • pipelines,
  • Remote Control.

Plate pasteurizers are more popular. They are able not only to quickly heat the dairy product, but also to withstand it for the right amount of time at a certain temperature, and then cool it down. The plate pasteurizer consists of:

  • pasteurization column,
  • Plate heat exchanger with cooling device,
  • centrifugal pump,
  • pipeline,
  • Control systems.
  • Long pasteurization bath

This device is capable of heating the product up to 95 degrees. A typical long pasteurization bath kit consists of:

  • double-wall bath with built-in electric heaters,
  • control unit,
  • motor,
  • drain cock,
  • pipe for pouring milk.

This type of pasteurizer is available in several versions that can hold from 60 to 2100 liters at a time. The average weight of the pasteurizer is 75 kg, and the weight of the 1000 liter pasteurizer is 340 kg.

Infrared pasteurizers

Infrared pasteurizers are used in various fields. They are used to pasteurize the milk of cows with mastitis. This dairy product is not suitable for humans, but is well suited for feeding calves. Another area of ​​application is to increase the shelf life of draft milk. Infrared pasteurizers are divided into three groups:

  • Capacity up to 300 liters per hour
  • Capacity from 500 to 1500 liters,
  • Capacity from 2000 to 500 liters.

Mini pasteurizers

Mini pasteurizers are produced for home use. They are designed for a volume of milk from 15 to 200 liters, the maximum heating temperature inside the device is 92 degrees. Typically, home pasteurizers come in the form of a cylinder with a handle. Pasteurized homemade milk can be stored for up to ten days.

The weight of the device depends on the internal volume. The minimum mass of a pasteurizer designed for 15 liters is six kilograms.

Milk pasteurization- this is a technology for disinfecting milk and extending its shelf life, which consists in a single heating of the liquid to a certain temperature for a certain time.

This technology is already more than one and a half hundred years old - it was first used in the middle of the 19th century by a microbiologist from France named Louis Pasteur. Actually, the name of the technology came from his last name.

There are various milk pasteurization modes- from long-term pasteurization (lasts 30-40 minutes at a temperature of 60 to 80 degrees) to instant (a few seconds at a temperature of 98 degrees). There is also ultra-pasteurization - it takes place at a temperature of more than 100 degrees.

Of all the modes of pasteurization in home cheese making, long-term pasteurization is most often used (more on that below).

Why is pasteurization necessary for cheese making? Can I use commercially already pasteurized milk?

The choice of milk for cheese making is a double-edged sword. If you bought store-bought milk, then it is already pasteurized, but the chance of getting cheese is 50/50. That is, either it works or it doesn't. And it is likely that with pasteurized store-bought milk, you will have to use all sorts of tricks, such as adding calcium chloride, so that you still get cheese.

Fresh farm unpasteurized milk, in turn, almost always gives a guaranteed result - with good ingredients and following the recipe, the cheese turns out to be almost excellent.

But unpasteurized milk can harbor certain threats in the form of unfriendly bacteria. Therefore, pasteurization is almost always required for such milk. And even the presence of veterinary documents for milk and the presence of a “verified” farmer does not guarantee you the absence of unwanted microbes.

Therefore, our advice is this: it is still better to pasteurize farm milk in order to prevent the development of pathogenic microflora in your cheese.

Milk pasteurization technology at home

To pasteurize milk at home, you will need the following equipment:

  • Saucepan with lid
  • slotted spoon or large wooden spoon/shovel

And you need to be patient.

  1. So, pour fresh milk into a saucepan, put it on medium heat and, stirring constantly, heat up to 72-74 degrees (use a thermometer). Some sources state that you need to heat up to 82, but this is a reinsurance (see table below on the page).
  2. Once the milk has reached the right temperature, close it with a lid and let it stand for 30 seconds.
  3. After 30 seconds, place the pan in a container of cold water (you can use a large sink or bath). Here you quickly cool it to the temperature required according to the recipe (from 22 to 38 degrees, depending on the type of cheese).

All! Milk is pasteurized. After that, you can go directly to cheese making.

According to this source, the use of a temperature at which tuberculosis bacteria are destroyed makes it possible to eliminate other bacteria that are found in milk and are often pathogenic. If the specified mode of pasteurization of milk is observed, up to 99% of the microflora of milk dies, not excluding mammakoki and Escherichia coli, which are harmful to cheese making.

By the way! Milk is not suitable for cheese making within two hours after milking! (it contains natural inhibitors that prevent the development of lactic acid bacteria). So if the milk is literally fresh, then you need to wait a couple of hours. Read more about the suitability of milk for cheese making.

Also a very important point : after pasteurization, milk becomes less cheesy, because. calcium ions are released from milk. And for coagulation (rennet coagulation) of milk, calcium ions are necessary. To make up for their deficiency, after pasteurization of milk, when making cheese, add to milk

Milk pasteurization or heat treatment is the process of heating milk from 63°C to a temperature close to its boiling point.

This process takes its name from the famous French scientist Louis Pasteur (1822-1892), who first used this method to eliminate microorganisms in wine and beer.
The effect of pasteurization on microorganisms present in milk depends on the temperature to which the milk is heated and the duration of holding at that temperature.

Pasteurization destroys bacteria, and sterilization (heating milk above the boiling point) immediately destroys spores. Boiling destroys the entire microflora of milk, except for spores that are resistant to boiling temperature. Pasteurization without a noticeable change in the organoleptic parameters of milk (taste, smell and texture) destroys tuberculosis, brucellosis and other pathogenic bacteria.

In ordinary skimmed milk, 99% of microbes die only under the condition of a good, reliable sterilization of equipment, tools, utensils used in the pasteurization process. Thus, the addition of contaminated milk containing 1 billion microbes 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 a more common and cheaper method of sterilizing milk.
Milk is also pasteurized during the production of all products from milk in order to protect them subsequently from undesirable processes that are caused by the vital activity of bacteria, and especially E. coli, butyric microbes, etc.

In practice, they use three modes of pasteurization:

  • with 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 certain 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 partly changes. But milk albumin undergoes the greatest action: 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), a precipitate is deposited - milk stone (burnt).

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.

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.