On Food and Cooking

many of its fat globules rise and form a fat-
rich layer at the top of the container. This
phenomenon is called creaming, and for
millennia it was the natural first step toward
obtaining fat-enriched cream and butter from
milk. In the 19th century, centrifuges were
developed to concentrate the fat globules
more rapidly and thoroughly, and
homogenization was invented to prevent
whole milk from separating in this way (p.
23). The globules rise because their fat is
lighter than water, but they rise much faster
than their buoyancy alone can account for. It
turns out that a number of minor milk proteins
attach themselves loosely to the fat globules
and knit together clusters of about a million
globules that have a stronger lift than single
globules do. Heat denatures these proteins and
prevents the globule clustering, so that the fat
globules in unhomogenized but pasteurized
milk rise more slowly into a shallower, less
distinct layer. Because of their small globules