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

嗯，酸奶就是酸了的牛奶，所以很难判断它是什么时候变酸的，因为它已经酸了。

Well, if you put milk out in the sun, eventually the milk will sour.

好吧，如果你把牛奶放在太阳下，最终牛奶会变酸的。

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.

这是我的最后一个例子。 物的保质期，即生菜变脆的时间， 或者牛奶开始变酸的时间。

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.

这家商店的风俗没落了，因为一个故事传开了，说她皱着眉头把她的小啤酒和其易损坏的商品变酸了。

In the 1850s, French microbiologist Louis Pasteur began to help the local beer and wine industries, whose products suffered from spoiling and souring.

在1850年代， 法国微生物学家路易·巴斯德开始帮助当地的啤酒和葡萄酒行业，这些产品的质量受到了变质和变酸的影响。

Narrator: While " Pinto Ben" hasn't gotten to the point of sour milk, the clear film base has started to discolor.

叙述者：虽然《Pinto Ben》还没到像变酸的牛奶那样糟糕的地步，但透明的胶片基底已经开始变色了。

That's what Rachel is asking Sergey, if he used milk that was not sour and that none of the ingredients were spoiled.

Rachel在问Sergey，是否用了没有变酸的牛奶， 并且所有材都没有变质。