buttermilk

詳細解釋：

but.ter.milk

n.（名詞）
The sour liquid that remains after the butterfat has been removed from whole milk or cream by churning.
酪乳：將乳脂從牛奶或一次提制的奶油中除去之後剩下的酸味液體
A cultured sour milk made by adding certain microorganisms to sweet milk.
優酪乳：在甜牛奶中加入某種微生物製得的發酵的酸味牛奶