Well, yogurt is soured milk, so it's difficult to say at which point it sours, because it's already sour.

嗯，酸奶就是酸了牛奶，所以很难是什么时候变酸，因为已经酸了。

The custom of the shop fell off, because a story got abroad that she soured her small beer and other damageable commodities, by scowling on them.

这家商店风俗没落了，因为一个故事传开了，说她皱着眉头把她啤酒和其他易损坏商品变酸了。

Here's our last example. They estimate a food's shelf life, that is how long the lettuce will be crisp,   or how long before the milk begins to sour.

这是我们最后一个例子。 他们估计食物保质期，即生菜变脆时间， 或者牛奶开始变酸时间。

It is desirable for a light frost to touch the cane to sweeten it, as persimmons and citrus must be touched, but a heavy frost ruins it, so that the stalks sour where they stand.

像柿子和柑橘一样， 需要轻霜接触甘蔗使其变甜， 但重霜会破坏， 以至于茎杆在们站立地方变酸。

Few things can age and sour a woman and destroy her looks as quickly as worry. Worry curdles the expression. It makes us clench our jaws and lines our faces with wrinkles. It forms a permanent scowl.

没有什么比忧虑更能让女人变老、变酸、毁容了。担心使表情凝固。让我们咬紧牙关，让我们脸上布满皱纹。形成了永久皱眉。