Lees (fermentation)

Lees are sedimentary 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. When brewing beer, this sediment is known as trub, not lees. However, when formed during secondary fermentation, yeast residual sediment is named lees for both wine and beer, or dregs for beer alone. This material is the source for most commercial tartaric acid, which is used in cooking and in organic chemistry.

The term in English derives from Middle English lie, from Anglo-French, from Medieval Latin lia.Webster's Third International Dictionary shows from lia, "probably of Celtic origin, akin to Old Irish lige (bed), Gaulish legasit (he laid) and Welsh llaid (mud)."

Normally, the wine is transferred to another container (racking), leaving this sediment behind. Some wines (notably Chardonnay, Champagne, and Muscadet) are sometimes aged for a time on the lees (a process known as sur lie), leading to a distinctive yeasty aroma and taste. The lees may be stirred (French: bâtonnage) for uptake of their flavour.

The lees are an important component in the making of ripasso, where the leftover lees from Amarone are used to impart more flavour and colour to partially aged Valpolicella.

Fujian red wine chicken is made from rice wine lees.