Lees are a mixture of dead yeast, grape skins, seeds stems, and tartrates, which are racked off and discarded during the winemaking process. Another type of lees, known as fine lees, is mostly made of dead yeast cells that gradually settle on the bottom of a fermentation vessel. Some wines spend extended amounts of time on the lees, imparting flavors of toast, bread-like aromas, cheese or buttermilk-like aromas, and sometimes sweet, nutty aromas.