1. Preparation materials: yogurt machine, yogurt (or yogurt powder), fresh milk or pure milk.
2. Disinfection: Wash the inner container of yogurt machine and scald it with boiling water for disinfection. After the milk is boiled, pour it into a sterilization container (the sterilized packaged pure milk does not need to be boiled).
3. Inoculation: cool the milk to 35℃ to 38℃, add yogurt or strains (yogurt should use active fermented yogurt with fresh production date, the ratio is 1:4), and stir evenly.
4. Fermentation: put the container filled with milk and strains into the yogurt machine, cover it and set the time (usually 8- 12 hours).
5. Check: After the time is up, open the lid and check whether the milk has solidified into yogurt. If it is not completely cured, you can wait for a while.
6. Enjoy: Pour the prepared yogurt into a bowl, add some honey or fruit, and enjoy.
Production principle:
The principle of making yogurt is to ferment lactose in milk by lactic acid bacteria, thus producing lactic acid, which makes milk solidify and turn sour. Specifically, when milk contains a lot of lactose, lactic acid bacteria decompose it into lactic acid through fermentation, and at the same time produce some by-products, such as acetic acid and carbon dioxide.
This process will lead to the decrease of pH value, and the casein in milk will start to solidify, forming the texture of yogurt. In the fermentation process, lactic acid bacteria will also produce some antibacterial substances, such as hydrogen peroxide, which can inhibit the growth of other harmful microorganisms, so yogurt has a certain antiseptic effect.
Besides lactic acid bacteria, the production of yogurt also needs some other conditions, such as suitable temperature and time. Usually, lactic acid bacteria grow and reproduce fastest at around 37℃, so before adding lactic acid bacteria to make yogurt, milk needs to be heated to this temperature. At the same time, the fermentation time also needs to be properly controlled, generally ranging from 4 to 8 hours.
Too short time will lead to incomplete fermentation, and too long time will lead to excessive acidification of milk. In addition, attention should be paid to sanitary conditions to avoid deterioration caused by miscellaneous bacteria pollution.