Lees

Lees is dead yeast cells that are left after fermentation. They become a silty material lying on the bottom of the vessel.

Lees can have an unpleasant aroma, which can be problematic for the wine. But they can also have a pleasant aroma, which can be beneficial for the wine. The winemaker decides whether to keep or remove the lees.

Leaving the lees in the wine is called sur lie (“on the lees”).