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" What's that brown stuff in the bottom of my pot? "

Dear Anne and Sue,

When I heat milk, there are sometimes brown scorched bits left on the bottom of the pan. I'm inquisitive, is this milk fat burning?



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Dear Jordie,

It's not likely milk fat that you see on the bottom of the pan, but coagulated proteins from the whey in the milk. Some of these proteins are very sensitive to heat. Lactalbumin, for example, begins to coagulate as low as 150° F (66° C). Once precipitated, milk proteins tend to scorch. That's why milk is best heated over very low heat or just briefly in the microwave oven, and why stirring is advised while milk is heating.

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.

Anne and Sue



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