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When you open a container of yogurt, you’ll often see liquid collected on top.
當你打開一盒酸奶后會發現，上面漂浮著一層液體。
Some people mix it back into the yogurt, and others drain it off. What is it, and where does it come from?
有人喜歡將其拌入酸奶中，而有的人會把這層液體倒掉。這層液體究竟是什么，它又從何而來？
To solve the mystery of the liquid in yogurt, let’s take a few steps back, to the milk that yogurt is made of.
為了揭開酸奶里這層液體的神秘面紗，咱們往回追溯，看看制作酸奶的原料—牛奶吧。
Milk has two different types of proteins.
牛奶有兩種不同類型的蛋白質。
Most of the proteins are casein proteins, and the rest are whey proteins–of curds and whey fame.
大部分蛋白質為酪蛋白，其余的是乳清蛋白，包括凝質和乳清。
If you look at a glass of milk, you can’t tell the casein from the whey.
如果你用肉眼觀察一杯牛奶是無法從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細菌來制作酸奶，那就另當別論了。
Yogurt-producing bacteria ferment the sugars in milk and produce an acid.
制作酸奶用的細菌會發酵牛奶中的糖并制成酸。
譯文為可可英語翻譯，未經授權請勿轉載!
