lees, old English word for the dregs or sediment that settles at the bottom of a container such as a fermentation vessel. Wine lees are made up of dead yeast cells, the cell membranes of pulp, stem and skin fragments, and insoluble salts and macromolecules that are deposited during the making and ageing of wine.
In the production of everyday wines, clear wine is separated from the lees as soon as possible after fermentation, to ensure that yeast autolysis is avoided and clarification and stabilization can be begun. Some wines, both red and, especially, white, may be deliberately left on some or all of of their fine lees (as opposed to the coarser gross lees, from the French grosses lies, off which most wines are racked early in their life if greater complexity and reduction of malic acid are desired), for some months in order to gain greater complexity of flavour. This is called lees contact.