Barm is the foam or scum that forms on the top of a fermenting liquid like beer, wine, or other alcoholic brews. This foam contains yeast and is traditionally used as a natural leavening agent in bread-making. Essentially, barm is a type of wild yeast harvested from fermenting liquids to help bread rise. Historically, before commercial yeast was widely available, bakers would use barm skimmed off fermenting beer or ale to leaven their bread, giving it distinctive flavors. Barm can also serve to start fermentation in new batches of liquor. The yeast species in barm is usually Saccharomyces cerevisiae, which is the same yeast used in brewing and baking today. In addition to its use as yeast for bread, "barm" also appears in culinary terms such as the "barm cake," a soft bread roll from Northwest England traditionally leavened with barm. In summary, barm is a natural yeast product from fermentation, historically significant in baking and brewing. It gives bread unique flavors and has been used since ancient times as a levener before modern yeast became common. If you want, barm can be recreated by mixing flour, beer, and sourdough starter or made from the natural foam of fermenting beverages. This explanation captures the essential definition and traditional uses of barm. Let me know if you want more details or recipes involving barm!
