For at least the last 7,000 years, humans have extracted a mixture of enzymes from the stomachs of cows and sheep and goats and added it to milk. This causes the milk to curdle—it's part of the cheese-making process.
在过去至少 7000 年里,人们从牛、绵羊和山羊的胃里提取出了多种酶的混合物,并把它们添加到牛奶里,让牛奶凝固——这是制作芝士的环节之一。