What You Need to Know
During fermentation lactose is converted by Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus into lactic acid, lowering the pH to about 4.5 and inducing casein coagulation. The acidified curd traps proteins while whey is expelled, and mild proteolysis at higher temperatures can alter texture. Cold straining at 4 °C concentrates solids and stabilizes the final spreadable consistency.
The Science
Primary Reaction
lactose → lactic acid (via S. thermophilus and L. delbrueckii subsp. bulgaricus)