In making yogurt why do you need to cool the milk to 50 degrees Celsius?

Answer 1

You have to cool the milk to 50 degrees celsius or less before adding the starter culture because otherwise all the microorganism you will use for fermentation will die and the fermentation won't take place. Most of the bacteria (Lactobacillus, usually) need 37 degrees celsius for growing and fermentation. Temperatures higher than their optimum temperature will decrease their grown and the fermentation process will be slow or can kill these bacteria.

Answer 2

Cooling the milk to 50 degrees Celsius before adding the yogurt culture encourages the growth of beneficial bacteria, such as Lactobacillus. This temperature range is ideal for the bacteria to thrive and ferment, which leads to the production of yogurt with a smooth texture and tangy flavor. Additionally, cooling the milk helps to prevent any undesirable bacteria from contaminating the yogurt culture.