Lees are the sediments of dead yeasts, tartrates and other insoluble material that settle at the bottom of wine (and beer, cider) containers after fermentation — divided into gross lees (coarse) and fine lees. Winemakers may age wine on its fine lees (sur lie, with bâtonnage stirring) to add body, creamy texture and complex flavours (notably in Muscadet and Champagne), or rack the wine off the lees to clarify and stabilise it. Prolonged contact with gross lees risks reductive off-flavours (hydrogen sulfide); spent lees are removed, and may be distilled into marc spirits, used as fertiliser or composted.