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Curd (Hindi दही dahi, Bengali দই doi, Tamil: തൈര് Thayir, Telgu: పెరుగు Perugu, Marathi: தயிர் Tayir ) is a traditional fermented milk product usually prepared from cow milk, and sometimes buffalo milk, or goat milk. It is popular throughout South Asian countries such as Bangladesh, India, Nepal, Pakistan, Sri Lanka, etc. The word curd is used in Indian English to refer to (naturally probiotic) 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 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 helps in fermentation of 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 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.
Buffalo curd (Sinhala: මුදවාපු මී කිරි mudavāpu meekiri, ) is a traditional type of yogurt prepared from water buffalo milk. It is popular throughout south Asian countries such as Bangladesh, India, Nepal, Pakistan, Sri Lanka, etc. Buffalo milk is traditionally better than cow milk due to its higher fat content making a thicker yogurt mass.  Mostly clay pots are used as packaging material for Buffalo curd.
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 include Lactococcus lactis, Streptococcus diacetylactis, Streptococcus cremoris, Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus.
Buffalo curd has a higher nutritional value of protein, fat, lactose, minerals and vitamins. It should have 7.5% of milk fat, 8.5% of milk solids and 4.5% of Milk acid (lactic acid).[further explanation needed] Quality of the curd totally 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.
Curd is an important part of everyday diet in the Indian subcontinent, both in slow cooked food and fast food.
Slow (cooked) food:
- Dahi chawal – curd rice
- Dahi kadhi – curd curry
- Doi maach – Bengali dish, fish in curd curry
- Coconut chutney - side dish for Idli/Dosa/Uttapam, south Indian cuisine
- Raita - side dish for Biryani
- Dahi baigan/Kathrikai thayir kothsu - Eggplant with curd, south Indian cuisine
- Perugu Pachadi - curd based dip, Andhra dish
- Thepla - served with plain curd, Gujrati dish
- Dahi vada / Dahi bhalla 
- Lassi : curd mixed with water and sweetner, usually sugar or molasses.
- Papri chaat
- Dahi puri - variation of Panipuri, using curd instead of tamarind water
- Dahi bhelpuri - variation of Bhelpuri, with curd on top
- Aloo tikki - plain curd is a side dish for Aloo tikki
- Aloo paratha - plain curd is a side dish for Aloo paratha
- Mishti doi - curd that is fermented after adding sweetner to milk, usually cane Jaggery or date palm jaggery.
- Caballero, B.; Finglas, P.; Toldra, F. (2015). Encyclopedia of Food and Health. Elsevier Science. pp. 345–351. ISBN 978-0-12-384953-3. Retrieved December 6, 2017.
- Discussion at StackExchange's "English language & usage" site
- Making yogurt -blog
- Codex Alimentarius Yogurt rules, FAO
- The secret of making soy yogurt without store bought culture
- Kristbergsson, Kristberg; Oliveira, Jorge. Traditional Foods: General and Consumer Aspects.
- "Curd and Treacle". Lanka Newspapers. 2008-10-18. Archived from the original on 2013-09-05. Retrieved 2009-08-31.
- Vohra, A.R. (2012). New Modern Cookery Book. V&S Publishers. p. 104. ISBN 978-93-5057-278-8. Retrieved December 6, 2017.
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