Understanding Thermization: A Heat Treatment for Milk Storage and Quality

Thermization of milk is a heat treatment distinct from pasteurization, specifically designed to control spoilage without significant alteration of the milk's properties. Unlike pasteurization, thermization lacks a legal definition or standardized criteria. The process involves heating milk to 62–65 °C for 10–20 seconds, followed by immediate refrigeration.

This treatment is ideally applied soon after milk collection and remains effective only if the thermized milk is kept at a low temperature, around 4 °C. Thermization significantly reduces spoilage bacteria with minimal impact on the milk's components, preserving its natural flavor. This makes it an excellent prepasteurization method to maintain milk quality during extended storage in insulated silos.

Thermization is also employed as a postpasteurization treatment for various dairy products. Its primary purpose is to protect against microorganisms, particularly Gram-negative psychotropic bacteria, which can proliferate during raw milk storage. The treatment allows milk to be stored below 8 °C (46 °F) for up to three days or at 0–1 °C (32–34 °F) for as long as seven days. Subsequently, the milk can undergo more rigorous heat treatments for extended preservation.

A critical aspect of thermization is the cooling phase before any reheating, which is necessary to delay or prevent the outgrowth of bacterial spores. This cooling step ensures that the milk remains safe and high-quality until it can be further processed or consumed.

In summary, thermization is a strategic heat treatment that extends the shelf life of milk by reducing spoilage bacteria while preserving its flavor and nutritional qualities. Although not legally defined like pasteurization, it serves as an effective measure for maintaining milk quality during storage and transportation.
Understanding Thermization: A Heat Treatment for Milk Storage and Quality

Ultra-high-temperature treatment of milk

Milk is usually considered as complete food because of its nutritional compositions. Milk is processed by ultra-heat treatment (UHT) with integrated aseptic packaging to increase the shelf life with sound quality.

UHT processing of milk denotes a continuous heating process at temperatures higher than 130 °C (usually 140 – 150 °C) for a holding period of a few seconds (usually 2-10s) followed by aseptic packaging to produce a ‘commercially sterile’ product with an anticipated shelf life of 6 months stored/distributed under ambient conditions. High hydrostatic pressure processing is a recent technology using pressure for a bactericidal effect.

Aseptic packaging involves placing a sterile product in a sterile package. Such processing must take place in a sterile environment.

The keeping quality test designed to establish the sterility of the product and the turbidity test used to ensure the product has not been subjected to excessive heat treatment.

The time-temperature combinations used in UHT systems are determined by the need to inactivate heat resistant bacterial endospores such as those of Bacillus stearothermophiles and the need to limit chemical changes which decrease the sensory and nutritional qualities of the product.

The most common methods of UHT heating use steam or superheated water as the heating medium although other less-common electro heating methods can be used. The steam-based methods use steam either directly or indirectly to heat the milk.
Ultra-high-temperature treatment of milk