Yogurt starter is a specific microbial culture material used to make yogurt, and different bacterial powders contain different strains. Yogurt starter powder generally contains Lactobacillus bulgaricus and Lactobacillus acidophilus, and Bifidobacterium BB- 12, which was specially selected by Kohansen in Denmark to produce probiotic dairy products. Now many bacterial powders contain Bifidobacterium BB- 12, such as Bifidobacterium chuanxiu.