Boiling the Wort

Appears in
On Food and Cooking

By Harold McGee

Published 2004

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Once the liquid wort has been drawn off the grain solids, the brewer runs it into a large metal tank, adds hops, and boils it vigorously for up to 90 minutes. Boiling converts the insoluble hop alpha acids into their soluble form and develops the beer’s bitterness, and inactivates the barley enzymes and so fixes the carbohydrate mix—a certain portion of sugar for the yeasts to convert into alcohol, a certain portion of dextrins for the beer’s body. It sterilizes the wort so that the brewing yeasts won’t have any competition during fermentation, and it concentrates the wort by evaporating off some of its water. Boiling deepens the wort’s color by encouraging browning reactions, mainly between the sugar maltose and the amino acid proline. And it begins the process of clarifying the brew by coagulating large proteins and causing them to bind with tannins from the barley hulls, form large masses, and precipitate out of the solution. When boiling is finished, the wort is strained, then cooled and aerated.