Cookbook:Buttermilk

Buttermilk or cultured buttermilk is a tangy liquid dairy product.

Characteristics
Buttermilk originally referred to the liquid left behind after churning butter —this was often tangy due to fermentation of the cream prior to churning, as well as low in fat due to the separation of the butter. Today, commercial cultured buttermilk is made separately from the butter churning process by simply inoculating low-fat milk with lactic acid bacteria.

Because most of the fat is removed with the butter, buttermilk is not very rich. It is sour and thicker than milk due to the acid's effect on the dairy. Buttermilk is sometimes available in a dry powdered form.

Selection and storage
Buttermilk should be stored in the fridge. It has a relatively long shelf life, but it will go bad.

Use
Buttermilk is quite popular as a refreshment in India, where it is made into a drink known as lassi. When used in baked goods, buttermilk tenderizes them in addition to contributing flavor and leavening (if combined with baking soda).

If you don't have buttermilk on hand, there are a couple acceptable substitutes. Plain kefir is very similar and can generally be substituted exactly. Sour milk can be made by adding a little vinegar or lemon/lime juice to milk, and this will contribute acidity. It will, however, have a different flavor profile and thickness. To avoid this, you can also dilute yogurt or sour cream with milk until the correct consistency.