🌡️ Sterilization

Milk sterilization is long heating above 100 °C, usually after the milk is already sealed in its pack. The milk is filled into bottles or cans, sealed and heated in an autoclave — a large vessel where steam is kept under pressure. Typical settings are 110–125 °C for anything from a few minutes to 40 minutes. In continuous tower sterilizers, bottles slowly pass through heating and cooling zones, and the whole cycle takes about an hour.

This heating destroys all microbes and their spores. Sealed sterilized milk keeps without a fridge for a very long time, up to a year. But long heating has a cost. The milk darkens and gets a noticeable “cooked,” caramel taste: milk sugar reacts with proteins (the Maillard reaction). More vitamin B1 and the amino acid lysine are lost than with UHT treatment.

In-pack sterilization is the older “relative” of UHT treatment. A way to sterilize condensed milk in sealed cans was developed in the early 1880s. Unsweetened condensed milk (evaporated milk) is still made this way: it is sterilized in cans at 110–120 °C for 15–20 minutes. UHT treatment heats milk for only a few seconds, so its taste is milder.