Thermization process

Thermal processing can be defined as the combination of temperature and time in order to reduce or destroy microbial activity, reduce or destroy enzyme activity and to produce physical or chemical changes to make the food meet a certain quality standard.

According to the EU regulations, thermization is a sub-pasteurization treatment, performed under mild conditions (i.e., 57–68 °C for no less than 15 s in a heat exchanger), so as to guarantee the preservation of phosphatase activity and, consequently, part of the indigenous microbiota.

Thermization targets pathogenic bacteria while leaving the good bacteria in the product. The low temperatures do not alter the structure and taste of the product. It is used as a pre-pasteurization treatment of raw milk to safeguard milk quality during prolonged storage in insulated silos.

The process is also used as a post-pasteurization treatment of dairy products. The treatment always causes the elimination of psychrotrophic bacteria and the reduction of total bacterial count, enabling thermized milk to be stored for up to 3 days longer at 8 °C.

Psychrotrophic bacteria grow at less than 7°C. Common species in cold stored milk, which is the storage norm in most jurisdictions, are Micrococcus, Bacillus, Staphylococcus, Pseudomonas, Flavobacterium, and coliforms.
Thermization process

Thermization of milk

Thermization of milk is a ‘heat treatment not equivalent to pasteurization’. There is no legal definition nor criteria for thermization. The thermization process is a subpasteurization heat treatment of milk at 62–65 °C for 10–20 s, followed by refrigeration.

Thermization should be applied soon after milk treatment and it is only effective if thermized milk is kept cool (4 °C).

Thermization markedly reduces the number of spoilage bacteria with minimum collateral heat damage to milk components and it does not cause changes in flavor. It is used as a prepasteurization treatment of raw milk to safeguard milk quality during prolonged storage in insulated silos. The process is also used as a postpasteurization treatment of dairy products.

The purpose of this treatment is to protect against microorganisms that may grow during storage of raw milk, especially Gram-negative psychotropic bacteria.

Thermization allows the milk to be stored below 8 °C (46 °F) for three days, or stored at 0–1 °C (32–34 °F) for seven days. Later, the milk may be given stronger heat treatment to be preserved longer. Cooling thermized milk before reheating is necessary to delay/prevent the outgrowth of bacterial spores.
Thermization of milk