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
