On Food and Cooking

fermented milks, in which the fermenting
microbes are evenly dispersed, kefir is
made by large, complex particles known as
kefir grains, which house a dozen or more
kinds of microbes, including lactobacilli,
lactococci, yeasts, and vinegar bacteria.
This symbiotic association grows at cool
room temperatures to produce a tart,
slightly alcoholic, effervescent, creamy
product.
The long evolution of cheese probably
began around 5,000 years ago, when people in
warm central Asia and the Middle East
learned that they could preserve naturally
soured, curdled milk by draining off the
watery whey and salting the concentrated
curds. At some point they also discovered that
the texture of the curd became more pliable
and more cohesive if the curdling took place
in an animal stomach or with pieces of
stomach in the same container. These first
cheeses may have resembled modern brine-