That's milk which has not undergone pasteurization, the century-old process of using heat to kill potentially harmful bacteria.

生鲜奶是未经巴氏杀菌处理过的牛奶。而巴氏杀菌是一种拥有历史利用温将潜在有菌杀灭的工艺。

This led to the invention of pasteurization, as you all know from your middle school science classes, but it also led to an understanding that fermentation was a biological process involving living organisms.

这导致了巴氏杀菌法的发明，正如你们在中学科学课上所知道的，但它也让人们得以理解发酵是一个涉及到生命有机体的生物过程。