Dahi or curd, also mosaru, dahi, thayir and perugu, is a traditional yogurt or fermented milk product originating from and popular throughout the Indian subcontinent. It is usually prepared from cows' milk, and sometimes buffalo milk or goat milk.[1] The word curd is used in Indian English to refer to homemade yogurt,[2][3] while the term yogurt refers to the pasteurized commercial variety known as "heat-treated fermented milk".[4]
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 (or their stems) 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.
After the starter is made, or saved from a previous batch of curd, milk is boiled and cooled. In a separate bowl, curd is mixed with its whey, and then mixed together with the milk. It is then left to sit undisturbed for 5 to 10 hours, until slightly sour, then refrigerated until consumption.
This practice can also be applied for making curd from milk substitutes, such as soy milk.[5]
Buffalo curd (Sinhala: මුදවාපු මී කිරි mudavāpu meekiri) is a traditional type of yogurt prepared from water buffalo milk. It is popular throughout the Indian subcontinent. Buffalo milk is traditionally considered better for making yogurt than cow milk due to its higher fat content making a thicker yogurt mass.[6] Buffalo curd is usually packaged in clay pots.
Buffalo curd is obtained by bacterial fermentation of buffalo milk. In this process, lactose in buffalo milk is converted into lactic acid using several micro-organisms. The species involved in the fermentation are the same as above.
Buffalo milk has higher amounts of protein, fat, lactose, minerals and vitamins than cow's milk. The quality of the curd depends on the starter culture. Fermentation also develops the characteristic flavor and colour of the product.
Buffalo curd can be made in both traditional and industrial forms. Traditionally, buffalo milk is filtered and boiled, the scum is removed and it is cooled to room temperature. A few spoonfuls of a previous batch of curd are added and it is then mixed well and poured into clay pots. These are sealed by wrapping a piece of paper over the pot and allowing it to stand for 12 hours.[7]
Curd is an important part of everyday diet in the Indian subcontinent, both in slow cooked food and fast food.
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