Curd

Curds are a dairy product obtained by curdling (coagulating) milk with rennet or any edible acidic substance such as lemon juice or vinegar, and then allowing it to set. The increased acidity causes the milk proteins (casein) to tangle into solid masses, or curds. The remaining liquid, which contains only whey proteins, is the whey. In cow's milk, 80% of the proteins are caseins. Milk that has been left to sour (raw milk alone or pasteurized milk with added lactic acid bacteria or yeast) will also naturally produce curds, and sour milk cheese is produced this way.

In the Indian subcontinent, the words "curd" or "curds" are wrongly used to refer to "yogurt". In the Indian subcontinent, another word "paneer" is used to denote a dairy product discussed in this article.

Uses
Curd products vary by region and include cottage cheese, curd cheese (both curdled by bacteria and sometimes also rennet), farmer cheese, pot cheese, queso blanco, and Indian paneer (milk curdled with lime juice). The word can also refer to a non-dairy substance of similar appearance or consistency, though in these cases a modifier or the word curdled is generally used.

In England, curds produced from the use of rennet are referred to as junket, with true curds and whey only occurring from the natural separation of milk due to its environment (temperature, acidity).

Cheese curds, drained of the whey and served without further processing or aging, are popular in some French-speaking regions of Canada, such as Quebec, parts of Ontario, and Atlantic Canada. In Quebec, Eastern Ontario and the Eastern provinces such as New Brunswick, cheese curds are popularly served with french fries and gravy as poutine. In some parts of the U.S., especially in Wisconsin, they are breaded and fried, or are eaten straight.

In Turkey, curds are called keş and are very common used as an aphrodisiac and for breakfast served on fried bread and also is eaten with macaroni in the provinces of Bolu and Zonguldak.

Formation
Lactobacillus is a kind of bacteria which can convert a sugar into an acid by means of fermentation. Milk contains a sugar called lactose, a disaccharide (compound sugar) made by the glycosidic bonding between glucose and galactose (monosaccharides). When milk is heated to a temperature of 30-40 °C and a small amount of old curd added to it, the lactobacillus in that curd sample starts to grow. These convert the lactose into lactic acid, which imparts the sour taste to curd.

Curds in song and poetry
Curds are mentioned in the Middle Irish parodic tale Aislinge Meic Con Glinne (The Vision of Mac Conglinne), the relevant portion of which reads:"Stately, pleasantly it sat, A compact house and strong. Then I went in: The door of it was dry meat, The threshold was bare bread, cheese-curds the sides. Smooth pillars of old cheese, And sappy bacon props Alternate ranged; Fine beams of mellow cream, White rafters - real curds, Kept up the house."

Curds also appear in the nursery rhyme Little Miss Muffet.