Yogurt is a dairy product fermented by fresh milk and yogurt starter. Yogurt starter is a special microbial culture material used to make yogurt. Starter plays a very important role in yogurt production, which is the basis and main reason for sour taste and fragrance of yogurt products. The quality of yogurt mainly depends on the quality type and activity of yogurt starter.

I suggest you don't use yogurt starter to make your own yogurt. Because there must be preservatives (potassium sorbate) in yogurt starter, there must be other food additives. You can buy a yogurt machine and a bag of good probiotic yogurt. Drink a part first, and the remaining 250 ml, you can add double (500 ml) pure milk (pure milk is heated and cooled to about 35-38 degrees). After stirring evenly, add two spoonfuls of sugar and put it into a yogurt machine to make yogurt. Then reserve a part of yogurt as an "appetizer" for making yogurt next time.