Lees (fermentation)

Lees refers to deposits of dead yeast or residual yeast and other particles that precipitate, or are carried by the action of "fining", to the bottom of a vat of wine after fermentation and aging. The yeast deposits in beer brewing are known as trub. However, yeast deposits from secondary fermentation of both wine and beer are referred to as lees. This material is the source for most commercial tartaric acid, which is used in cooking and in organic chemistry.