Plural of barm; yeasts, fermented sediments, or foam from fermentation; foam on water.
From 'barm' (yeast, from Old English beorma) with regular English plural '-s.' Appears in brewing, baking, and maritime contexts where foam and froth were important indicators.
Medieval sailors called the ocean foam on storm waves 'barms'—using the same word for beer yeast foam because the visual similarity made language memorable and poetic.
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