What are "lees"?

Lees are a natural byproduct of the wine fermentation and ageing process, and refer to the deposits of dead yeast cells, grape skin particles, and other solids that settle at the bottom of a wine barrel or bottle. During the fermentation process, yeast consumes the sugar in grape juice and produces alcohol and carbon dioxide. After the fermentation is complete, the yeast cells die off and settle to the bottom of the container, forming a layer of sediment known as lees. The presence of lees can have a significant impact on the flavor and texture of the wine, with some winemakers choosing to leave the wine in contact with the lees for an extended period of time in order to enhance the wine's complexity and richness. This process, known as sur lie ageing, can help to soften tannins and add a creamy texture to the wine. Lees can also be stirred or "battonage" in order to distribute the yeast and solids throughout the wine, which can enhance its flavor and aroma.