Yogurt culture refers to the specific strains of beneficial bacteria—mainly Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus—used to ferment milk into yogurt. These cultures convert lactose into lactic acid, thickening the milk and giving yogurt its characteristic tangy flavor and creamy texture. Some yogurt cultures also include probiotic strains for added health benefits. They are essential for producing consistent taste, texture, and nutritional qualities in yogurt products.