时差N小时 酸奶中含有神秘液体(上)（在线收听）

When you open a container of yogurt, you’ll often see liquid collected on top.

当你打开一盒酸奶后会发现，上面漂浮着一层液体。

Some people mix it back into the yogurt, and others drain it off. What is it, and where does it come from?

有人喜欢将其拌入酸奶中，而有的人会把这层液体倒掉。这层液体究竟是什么，它又从何而来？

To solve the mystery of the liquid in yogurt, let’s take a few steps back, to the milk that yogurt is made of.

为了揭开酸奶里这层液体的神秘面纱，咱们往回追溯，看看制作酸奶的原料—牛奶吧。

Milk has two different types of proteins.

牛奶有两种不同类型的蛋白质。

Most of the proteins are casein proteins, and the rest are whey proteins–of curds and whey fame.

大部分蛋白质为酪蛋白，其余的是乳清蛋白，包括凝质和乳清。

If you look at a glass of milk, you can’t tell the casein from the whey.

如果你用肉眼观察一杯牛奶是无法从中分辨出酪蛋白和乳清的。

But that changes when special bacteria are added to milk to make yogurt.

但是往牛奶中加入特殊的细菌来制作酸奶，那就另当别论了。

Yogurt-producing bacteria ferment the sugar