What was in the live yogurt that would help to turn fresh milk into yogurt?

Live yogurt contains specific strains of beneficial bacteria, primarily Lactobacillus bulgaricus and Streptococcus thermophilus, which are essential for the fermentation process. When fresh milk is inoculated with these live cultures, they ferment the lactose (milk sugar) into lactic acid. This acidification thickens the milk and gives yogurt its characteristic tangy flavor and creamy texture. The live cultures also contribute to the yogurt's probiotic benefits.