The main (starter) cultures in yogu

The main (starter) cultures in yogurt are Lactobacillus bulgaricus andStreptococcus thermophilus. The function of the starter cultures is to ferment lactose (milk sugar) to produce lactic acid. The increase in lactic acid decreases pH and causes the milk to clot, or form the soft gel that is characteristic of yogurt. The fermentation of lactose also produces the flavor compounds that are characteristic of yogurt. Lactobacillus bulgaricus andStreptococcus thermophilus are the only 2 cultures required by law (CFR) to be present in yogurt