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Heat treatment is used in the making of most foodstuffs, e.g. milk and other dairy products, meat and semi-finished goods made from meat, sausages, various beverages, fruit and vegetable-based semi-finished goods, purees, various types of canned food, and beer.

In the food industry, three approaches are used for subjecting products to high temperatures:

Sterilization is the process of heating products to temperatures over 100 °C, and then holding the temperature there for a time that depends on the organoleptic requirements for your products. This process ensures that all vegetative forms of microorganisms and spores are destroyed, which increases the product’s shelf life.

Pasteurization is a process meant to destroy vegetative forms of microorganisms by heating the product to 100 °C once and for a time that is not held. Pasteurization differs: long-time pasteurization (up to 40 minutes), short-time pasteurization (up to 1 minute), and instant pasteurization in a flow.

Ultra-pasteurization is subjecting food products to a temperature higher than 100 °C for a span of several seconds, immediately followed by cooling down to 5 °C.

The safety and preservation (and with minimal biochemical changes) of the finished product can ensured by high-temperature processing with holding times that are correctly calculated based on the type of product, its pH, degree of bacterial contamination, amount, and packaging.

Synonyms: pasteurizer, milk pasteurizer, beer pasteurizer, industrial sterilizer, sterilizing in containers, pasteurizing in containers, steam sterilizer, vacuum sterilizer, heat sterilization in containers, autoclave, vat pasteurizer, retort plants.

Sterilization is heat treatment of products at high temperature (over 100 °C) intended to fully eradicate microorganisms and spores.

Sterilizers are used to process meat, vegetable, fish, and dairy products, various beverages, and other foodstuffs. Also, unlike pasteurization, sterilization is widely used in the canning industry, since it ensures that pathogenic organisms cannot develop inside the hermetically sealed packaging.

How sterilizers are classified:

By design type

Vertical

Horizontal

By method of action

Thermal

Microwave/electromagnetic

Hydrostatic

By heating medium

Electric

Water

Steam

By operating mode

Periodic

Continuous operation

By plant type

Tabletop

Floor

Embedded

Today the following kinds of sterilizers are used in the food industry:

Thermal sterilizers are the most commonly used. The choice of sterilization mode, as mentioned earlier, depends on the type of container, the consistency and amount of the sterilized object, and a number of other factors.

Autoclaves are none other than a batch sterilizer. When sterilizing products at relatively low temperatures (up to 100 °C), open devices that work periodically are used. If the processing temperature exceeds 100 °C, sealed devices that run continuously are used. This equipment finds application in the making of all kinds of canned food (meat, fish, vegetable, dairy).

Microwave (electromagnetic) sterilization is today very intensively studied and applied, as it can significantly speed up the sterilization stage. Unlike the commonly used thermal method, microwave sterilization helps prevent the product from being microbiologically contaminated again when it is packaged, and this approach also ensures a long shelf life, at least 9–12 months. Hydrostatic sterilization is a unique but very costly method, as it requires that an entire facility be built for it. This method works on products both inside containers and without. However, only products that do not have cavities filled with air can be processed hydrostatically.

Various types of sterilizers are used in many fields: in cosmetology, in medicine, and in the food industry.


Values for sterilization of products in containers*

Product type

Heat treatment, °C

Processing time, minutes

Stewed meat (beef, pork)

120

105–125

Canned fish

115

80

Canned vegetables

100–120

28–52

Canned mushrooms

116–120

50–75

Fruit preserves (apple, cherry, etc.)

100

50–60

Natural fruit juice (apple, pineapple, grape, cherry)

85

40

Milk

135–140

2–3 seconds

*Values will differ for each specific model.

Pasteurization.

A pasteurizer is a device in which products are treated at high temperatures (up to 100 °C). The main goal of the pasteurization process is to eradicate all vegetative forms of microorganisms (e.g. E. coli, M. tuberculosis, brucellosis, etc.).

A pasteurization stage is generally part of the production process for products having a liquid consistency, such as milk, kefir, and purees.

Subjecting products to a pasteurizer ensures that all vegetative forms of microorganisms are eradicated, while sterilization guarantees that their spores are reduced to a minimum. At the same time, products retain their appearance and their main share of vitamins and minerals. Pasteurization can be applied to endow products with specific organoleptic properties.

How pasteurizers are classified:

By design type

Tank

Flow-through:

       a) Tubular

       b) Plate

       c) Steam-contact

Centrifugal

According to operating mode

Periodic

Continuous operation

By product processing type

thermal

cold (processing is carried out by infrared or ultraviolet radiation, the effect of ultrasound or radio waves).

By number of sections:

single-section;

dual-section; 

multi-section.

Vat pasteurizers are widely used in the production of milk and fermented-milk products.

A vat pasteurizer serves for:

  • Heating milk up to the pasteurization temperature and then cooling it.
  • Production of fermented-milk products.

A vat pasteurizer consists of a voluminous, cylindrically shaped tank that stands on strong supports, ensuring complete heat insulation. The vat pasteurizer can include components that ensure preservation of dairy products.

The main advantages of a vat pasteurizer are its simple design, guaranteed reliability and, most importantly, the fact that it is manufactured from materials that do not affect the state of food products.

Pasteurization (ULT) is employed in the making of most products and exists in different versions. Processing is carried out consecutively over three areas: heating, pasteurization, and then finally the cooling section. Pasteurization of canned foods is done in plants of a belt or conveyor type. Liquid products are pasteurized in units of flow-through, plate, or tubular type. Tank pasteurizers that operate periodically, plants based on plate and tubular designs, as well as combined devices, are used for processing milk and dairy products. Steam or hot water serves as the heating medium.
The way that a tubular pasteurizer works is quite simple: the product, heated to 50 °C is sent by means of a pump through the dairy pipeline and into the tubing of the operating cylinder. At the same time, hot water is sent through the inter-pipe space of the cylinders. The speed at which milk is supplied through the pipes, and how long the process takes, depends on the type of product and pasteurization mode.

Once the pasteurization process is complete, the product must be cooled to a temperature below 10 °C, since some cells of heat-resistant microorganisms may remain. For this cooling sections are used, where the product is cooled naturally or by means of cold water supplied through the interwall space.

Pasteurization and cooling plants are used in production for providing pasteurization and then cooling the finished product. In terms of their design, they are a multi-section plate device and they are used in the making of many dairy products such as yogurt, cream, kefir, ice cream, as well as honey, jam, baby food, and ketchup.

Many pasteurization plants are equipped with a chiller, which includes a filtration system, a pump (the specific design of which depends on the product), and temperature sensors. These work in the same way as the pasteurizers themselves, but with cold water (below 5 °C) serving as the heat-transfer medium.

Ultra-pasteurization (UHT) is a process by which products are treated to high temperatures for a short amount of time (2–3 seconds, 135–150 °C.), after which they are cooled to 4–5 °C.

The UHT approach allows significantly lengthening products’ shelf life because microorganisms are completely eradicated, yet all nutrients and taste properties are retained.

An ultra-pasteurization stage is often part of the production process when producing milk and dairy products. It is carried out under sterile conditions in special UHT plants. As packaging, multilayered hermetically sealed packaging (Tetrapak) is used.

Processing can be done in one of two ways:

  • Through contact between the heated surface and the product, at a temperature of 125–140 °C
  • Through contact with sterile steam at a temperature of 135–140 °C.

Example modes for processing* milk, ingredients for dairy products (butter, kefir, sour cream, curd cheese, yogurt, ayran, etc.):

Temperature, °C

Holding time

Type of pasteurization

63**

30 minutes

Long-time

72 **

15 seconds

Short-time

89

1.0 seconds

Instant

90

0.5 seconds

94

0.1 seconds

96

0.05 seconds

100

0.01 seconds

138

2.0 seconds

Ultra-pasteurization

** With fat content of 10% over higher, or if the product containers sweeteners, the temperature must be raised by 3 °C.

Product type

Temperature, °C

Holding time

Packaged milk

72–76

20–25 seconds

Fermented-milk drinks

80

30 minutes

85

10 minutes

90

5 minutes

95

2 minutes

100

1 minutes

Curd cheese and other dairy products

72–80

15–18 seconds

Beer

75

1 second (in a flow)

Honey

80

4 minutes

 *Values will differ for each specific model.

An undeniable advantage of this equipment is that it prevents products from burning, and also that heating up happens quickly.

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