On Food and Cooking

The Importance of a Cold Start and
Uncovered, Slow Heating After the blanching
or browning, the meat solids are started in an
uncovered pot of cold water, which the cook
brings slowly to a gentle simmer and keeps
there, regularly skimming off the fat and
scum that accumulate at the surface. The cold
start and slow heating allow the soluble
proteins to escape the solids and coagulate
slowly, forming large aggregates that either
rise to the surface and are easily skimmed off,
or settle onto the sides and bottom. A hot start
produces many separate and tiny protein
particles that remain suspended and cloud the
stock; and a boil churns particles and fat
droplets into a cloudy suspension and
emulsion. The pot is left uncovered for
several reasons. Because this allows water to
evaporate and cool the surface, it makes it less
likely that the stock will boil. It also
dehydrates the surface scum, which becomes
more insoluble and easier to skim. And it