What You Need to Know
During fermentation, Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus metabolize lactose via glycolysis, yielding lactic acid and CO₂. The acidification lowers the pH to 4.5–4.8, which curdles milk proteins into a smooth matrix. Post‑fermentation sugar addition can buffer acidity and enhance mouthfeel without inhibiting the cultures.
The Science
Primary Reaction
lactose → lactic acid + CO₂ (via glycolysis by S. thermophilus and L. delbrueckii subsp. bulgaricus)