Many Food Molecules Can’T Change Phase

Appears in
On Food and Cooking

By Harold McGee

Published 2004

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Most of the molecules that the cook works with can’t simply change from one phase to another when heated. Instead, they react to form entirely different kinds of molecules. This is because food molecules are large, and form so many weak bonds between molecules that they’re in fact held very strongly together. It takes as much energy to break them apart from each other as it does to break the molecules themselves apart: and so rather than melting or evaporating, the molecules become transformed. For example, sugar will melt from a solid into a liquid, but rather than then vaporize into a gas as water does, it breaks apart and forms hundreds of new compounds: a process we call caramelization. Fats and oils melt, but break down and smoke before they begin to boil. Starch, which is a long chain of sugar molecules joined together, won’t even melt: it and proteins, also very large molecules, begin to break down as solids.