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In the process of brewing beer, trub is the term used for the lees, or layer of sediment, left at the bottom of the fermenter after the yeast has completed the bulk of the fermentation. It is composed mainly of heavy fats, proteins, and inactive yeast.
Trub also refers to the material, along with hop debris, left in the boil kettle or hopback after the wort has been transferred and cooled. Brewers generally prefer that the bulk of the trub be left in the kettle rather than stay in contact with the fermenting wort. Although it contains yeast nutrients, its presence can impart off-flavors in the finished beer.
The term has its origins in the German word trübe (also trüb), which means cloudy, via the brewing and winemaking terms Trubstoff (cloudy + material) and Weintrub (wine + cloudy).
