What are lees in wine?
I sometimes find myself talking about Lees, and realise people don't know what I am talking about! Here is an explanation from Decanter Magazine
The lees in wine are essentially the dead yeast cells, leftover from the fermentation process. There are two kinds of lees; gross lees and fine lees.
Gross lees refers to the sediment that forms in the wine, and tend to naturally fall to the bottom of the wine vessel. They are normally removed from the wine soon after fermentation has ceased.
Fine lees are smaller particles that settle more slowly in the wine. They can also be filtered out of the wine, but some winemakers choose to leave them in for differing lengths of time in an effort to enhance the complexity of the wine.
The flavour of lees
Leaving the fine lees with a white wine develops further flavours and adds body.
Almond, hay and yeasty aromas and flavours can all be the results of spending some time ‘sur lie’ (on the lees).