Lees (fermentation)

Lees from Merlot after 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.^[1]

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 (bâtonage in French) in order to promote uptake of the lees' 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.

Sur lie

A French Muscadet white wine from the Northwestern region that has been aged sur lie.

Lees in a glass

Sur lie literally translates from French as 'on lees'. 'Sur lie' wines are bottled directly from the lees without racking (a process for filtering the wine). In the case of great Chardonnay, such as Montrachet, this adds a toasty, nutty "hazelnut" quality and additional depth and complexity, especially on the finish. Chemically this can alter the oak flavour molecules increasing the integration, and making the oak seem less obtrusive to the palate. This is desirable because oak tannins are a polyphenolic acid, and can be harsh. This process can also give an added freshness and creaminess to the wine, and improve color and clarity. Muscadet is made in this fashion. The effect of the lees during bottle fermentation for at least 18 months on Champagne is considerable. The "bready" toasty notes associated with some of the greatest sparkling wines made are the result of 'sur lie' aging.^[2]

Other uses

Beer on lees (trub) is also sometimes made. Many of the beers offered by the Quebec, Canada based Unibroue are on lees.

Light lees protocol

A process in which yeast is added to wine that has completed primary fermentation. This secondary yeast addition typically remains in the wine from two to eight weeks, depending on the wine maker's goals. The yeast is stirred (bâtonage) frequently during the protocol, and racked off when the protocol is complete. Also known as secondary autolysis, a light lees protocol releases additional mannoproteins and polysaccharides that can influence the flavour and mouth feel of the wine.

References

1. J.-M. Kassaian "Tartaric acid" in Ullmann's Encyclopedia of Industrial Chemistry; VCH: Weinheim, Germany, 2002, 35, 671-678. doi:10.1002/14356007.a26_163
2. J. Robinson (ed) "The Oxford Companion to Wine" Third Edition pg 669 Oxford University Press 2006 ISBN 0198609906