🔄 Fermentation

Fermentation turns milk into a fermented milk product with the help of bacteria. Lactic acid bacteria feed on milk sugar, lactose, and turn it into lactic acid. The milk becomes sour. The acid makes the protein casein link up into a mesh, and the milk thickens into a soft curd.

Different products need different bacteria and temperatures. Yogurt is made with heat-loving bacteria, Lactobacillus bulgaricus and Streptococcus thermophilus. The milk is first heated to 90–95 °C, cooled to 40–45 °C, the starter is added, and it is kept warm for several hours until it is sour enough. Cream for sour cream is fermented at 18–21 °C for almost a day. In kefir grains, yeasts live alongside the bacteria. They make a little alcohol and carbon dioxide, which gives kefir its slight fizz.

Fermentation is one of the oldest ways to preserve milk. The first fermented milk products were most likely made by accident by nomads in the Middle East. The acid holds back harmful germs, and there is less lactose left, so people with lactose intolerance often handle these foods better. This is how kefir, yogurt, soured milk, ryazhenka, ayran, matsoni, skyr, dahi and many other products are made.