Stability in Cooking

Appears in
On Food and Cooking

By Harold McGee

Published 2004

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How does a high fat content permit the cook to boil a mixture of heavy cream and salty or acidic ingredients without curdling it, as when dissolving pan solids or thickening a sauce? The key seems to be the ability of the fat globule’s surface membrane to latch onto a certain amount of the major milk protein, casein, when milk is heated. If the fat globules account for 25% or more of the cream’s weight, then there’s a sufficient area of globule surface to take most of the casein out of circulation, and no casein curds can form. At lower fat levels, there’s both a smaller globule surface area and a greater proportion of the casein-carrying water phase. Now the globule surfaces can only absorb a small fraction of the casein, and the rest bonds together and coagulates when heated. (This is why acid-curdled mascarpone cheese can be made from light cream, but not from heavy cream.)