Please kindly ask, why is the surface of yogurt made by commercial yogurt machine yellow?

Is the surface of yogurt yellow? Do you have milk skins? The reason may be: 1, the reduced milk (milk powder) you use to make yogurt is caused by heating sterilization for a long time and high temperature. 2. When making yogurt, the container is not sealed, and the color becomes darker due to the evaporation of water.

Suggestion: the container of yogurt should be sealed, because lactic acid bacteria belong to facultative anaerobic bacteria, and oxygen is rarely conducive to its growth. Do a good job in purchasing pasteurized milk without antibiotics (that is, milk produced by disease-free cows without antibiotics). Milk powder is not safe!