barm
/bɑrm/
noun
- The froth or foam that forms on top of fermenting malt liquors, such as beer or ale; used historically in baking as a leavening agent.
- A thick layer of barm covered the surface of the ale as it fermented.
- The brewer skimmed the barm from the top of the fermentation vat.
- In old recipes, barm was often used instead of commercial yeast to make bread rise.