Dahi

Curd, also mosaru or dahi or Thayir or Perugu, is a traditional yogurt or fermented milk product, originating from and popular throughout the Indian subcontinent. It is usually prepared from cow's milk, and sometimes buffalo milk or goat milk. The word curd is used in Indian English to refer to homemade yogurt, while the term yogurt refers to the pasteurized commercial variety known as heat-treated fermented milk. Curd is made by bacterial fermentation of milk. In this process, lactose in milk is converted into lactic acid by several probiotic microorganisms. The species involved in the fermentation depends on the temperature and humidity of the environment and may include Lactococcus lactis, Streptococcus diacetylactis, Streptococcus cremoris, Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus. Curd starter is sometimes made with dried red chillies in hot milk. Milk is boiled and then allowed to cool for a while. When lukewarm, dried chili peppers or their stems are added. The reason for this tradition is that dried chillies are rich in a type of lactobacilli, the bacteria that help ferment milk to form curd. The bowl is then kept undisturbed in a warm place for 5 to 10 hours.

Source: Wikipedia