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If
you're a coffee drinker, you've probably noticed the
tendency of milk proteins to coagulate. Milk that's
been sitting out too long, or that's slightly unstable
because it's close to souring, coagulates in little
bits on the surface as soon as it's been added to hot
coffee.
The mineral calcium phosphate precipitates when heated,
contributing to the scum you see on the bottom of the
pan.
Interestingly, the fat in milk can actually insulate
some of the proteins from dramatic changes. So cream
in your coffee is less likely to curdle than milk. Likewise,
heavy cream (with a higher fat content) can be used
in a silky reduction sauce, while regular milk will
curdle at high heat.
Like many of the foods we use every day, milk, too,
contains some fascinating and useful tidbits.
Regards,
Anne and Sue
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