Heat treatment of milk

Content

Introduction

Raw milk, intended for marketing for human consumption, must be treated with high temperatures (heat treatment) before packaging which must take place in closed containers.

All companies that start producing raw milk for human consumption must be registered with the Veterinary Prevention Departments that carry out the checks.

The heat treatments that guarantee the safety of the milk are:

  • pasteurization
  • sterilization

Pasteurization

Pasteurization consists in exposing raw milk to a high temperature for a short period of time (generally + 71.7 ° C for 15 seconds).

The regulations in force distinguish at least 5 types of pasteurized milk:

  • high quality pasteurized fresh milk
  • fresh pasteurized milk
  • microfiltered pasteurized milk
  • pasteurized milk
  • high temperature pasteurized milk and ESL (extended shelf life, from the English Extended Shelf-Life)

Raw milk intended to be used for the production of high quality pasteurized fresh milk, within two hours of milking it must be immediately filtered and refrigerated at a maximum temperature of +6 ° C and must be kept at this temperature, or at lower temperatures, pending transfer to the factory where the heat treatment will take place.

High quality pasteurized fresh milk, according to the requirements set by DM 185/1991, must contain at least 15.5% of undenatured whey proteins (in other words, whey proteins not damaged by heat), a greater quantity than the one present in fresh pasteurized milk "traditional". Starting from a better raw material, the heat treatment can be lighter (about 2 ° C lower than the common pasteurization), with less repercussions on the chemical-physical composition of the milk.

With the wording pasteurized milk microfiltered it indicates the treatment to which the milk is subjected to remove, through the use of special filter membranes, most of the germs present. Since microfiltration reduces the bacterial content, the milk can be pasteurized at lower temperatures. The storage time it is about double that of pasteurized milk and the nutritional characteristics are very similar.

The high temperature pasteurized milk and ESL it is subjected to heating between 80 and 135 ° C for a very short time (for example, for one second). After treatment, the milk is packaged in germ-free (aseptic) containers that allow it to be stored for a long time (25-30 days) at temperatures no higher than + 6 ° C (refrigerated conditions).

With pasteurization, there is a limited reduction of some nutrients, such as the B vitamins, water-soluble, originally present in milk. The main difference with respect to raw milk, that is to say that just milked, concerns the taste because the heating modifies the aromatic component of the milk a little.

Sterilization

Sterilization is a treatment that consists in the continuous heating of raw milk, at least 135 ° C for no less than a second or at lower temperatures (116-120 ° C) for longer times (about 20 minutes), in order to eliminate microorganisms and spores.

Sterilized milk is packaged in sterile and opaque containers in order to minimize chemical, physical, odor and taste (organoleptic characteristics) variations.

According to the regulations in force, sterilized milk is distinguished in:

  • long-life sterilized milk
  • long-life UHT milk

If sterilization is performed in closed containers for about 20 minutes at 116-120 ° C, this is referred to as sterilized milk; if, on the other hand, the milk is heated to 131-150 ° C for 1-5 seconds, by direct or indirect contact (heat exchangers) with water vapor, and then packaged in sterile containers, the UHT sterilized milk (very high temperatures, from English ultra-high temperatures). The conservation of these two products is respectively 6 months for sterilized milk and 3-6 months for UHT milk.

For both, the Minimum term of conservation it is established by the individual producer who assumes responsibility for it. Milk sterilized with both of the procedures described can be stored at room temperature but, once the package has been opened, it must be kept in the fridge and consumed within 3-4 days.

The advantage of sterilization consists not only in longer storage times but also in making transport and storage easier and in superior hygienic safety.

The higher temperatures to which milk is subjected in sterilization compared to pasteurization (thermal stress) result in a consistent loss of so-called vitamins water-soluble, not very resistant to heat, such as folic acid and vitamins B1 and B12. On the contrary, vitamin B2 is more sensitive to the action of light, so it is important that the containers are not transparent.

For UHT milk, however, since treatment times are very short, these are "acceptable" reductions in nutrients, especially when the overall diet is varied and balanced.

The choice of pasteurized or sterilized milk often depends on issues of convenience (for example, not having to go shopping every day) and taste (milk lovers struggle to accept the taste of sterilized milk, which has a hint of of "cotto").

In-depth link

State-Regions Agreement. Guidelines for the execution of controls aimed at guaranteeing food safety in the context of the production and placing on the market of milk for heat treatment and transformation (OJ 133 09/06/2008)

Milk package 2013

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