The basic principle of homemade yogurt is: inoculate lactic acid bacteria into milk and let it reproduce at a suitable temperature (generally 42℃-45℃). Under the action of lactic acid, the acidity of milk fermentation broth will gradually decrease. When the pH value reaches about 4.6, casein in milk will slowly precipitate and form delicate jelly.
In this step, the temperature of 42℃-45℃ is difficult to master and realize in China, so it is easy to produce a large number of bacteria in the fermentation process of lactic acid bacteria.
As far as strains are concerned, the fermented strains bought by ourselves are not safe, and the freeze-dried strains bought online will be affected by temperature and other factors during transportation, and it is easy to lose their activity. Some people will choose leftover yogurt as a primer for inoculation, but inoculation needs to be carried out under aseptic conditions, which is not available at home.
If you want to make yogurt at home, you need to buy professional instruments. The raw milk used and all utensils in contact with it, including fermentation containers and stirring utensils, must be sterilized by boiling or blanching. When selecting strains, try to choose a single strain to ensure health and safety.