Buttermilk 解釋....?

Buttermilk is the liquid left over after producing butter from full-cream milk during the churning process. It has a slightly sour taste. It is quite popular as a refreshment in India. Many breads are made with buttermilk, and it is also used in creamy soups and sauces.
In supermarkets, we can find cultured buttermilk, that is, milk to which lactic acid bacteria have been added to simulate the traditional product. The sour taste, or tartness of "cultured buttermilk" is a result of a fermentation process in which the bacteria turn lactose into lactic acid (that is we cannot find the "true" buttermilk in supermarkets).

Cultured buttermilk is probably the easiest and most fool proof fermented milk product to make. (Note that cultured is different than "old fashioned buttermilk.") All you need is active cultured buttermilk for the starter, and fresh milk for it to act on (store bought is fine). The formation of buttermilk is based on the fermentation by the starter bacteria which turns milk sugar (lactose) into lactic acid. As lactic acid is formed, the pH of the milk drops and it gets tart. Milk proteins, most notably casein, are no longer as soluble under acid conditions and they precipitate out, causing what we recognize as clabbering. Thus the two marked characteristics of buttermilk, its tartness and its thickened nature, are both explained by the presence or the action of lactic acid. Additional by-products of fermentation give subtle variations in buttermilk flavor.
The acidity of buttermilk also explains its long refrigerator shelf life. Acid is a natural preservative because it inhibits the growth of pathogenic bacteria. Thus buttermilk keeps easily for weeks in your refrigerator. If you keep it longer, it may develop mold on the inner walls of the jar. This mold belongs to the same group of fungi which grow on cheese and is not dangerous. Remove it and the buttermilk can still be used for baking. However, because the desired bacteria may have died in older samples, buttermilk older than three to four weeks may not work as an inoculum to make buttermilk.

SOUR CREAM can be made with the same procedureas buttermilk, using one cup of cream mixed thoroughly with 2 Tbl fresh active buttermilk and letting it sit for 12-24 hours at room temperature. The higher butterfat in the cream, the thicker the finished sour cream.

中文名： 酸奶
英文名： ButterMilk
英文簡寫： 無

分類： 乳製品
說明：
又稱發酵奶。是將培植細菌（酵母菌）加入脫酯牛奶（skim milk）中以改變牛奶的口味、化學組織。是味道較強烈的牛奶，它是用來做奶油時所剩下來的副產品。味道微酸。

酸奶的替代方法：

用 2/3 杯的低脂優格加上1/3杯的全脂或低脂牛奶來取代一杯的 buttermilk。

一杯的 buttermilk 可用一大匙的白醋或檸檬汁再加上牛奶使成一杯量，不需攪拌，靜置5分鐘後就可以當Buttermilk 的替代品了。