What on Earth Are Lees?

No, not Lee jeans. Lees is a term for dead yeast cells and other particles remaining in wine after fermentation. If you notice some funky tan-colored sediment or mud at the bottom of the fermenting container (tank, barrel or bottle) – that’s the lees.

The sediment might not look so appealing, but it isn’t all bad. While a lot of red wines will be removed from the sediment right after fermentation, some wines are left to age on the fine lees (the dead yeast cells rather than the bigger grape particles) because the dead yeast cells add more texture, flavor and aroma.

This aging process is known as “sur lie,” French for “on the lees.” During this aging process, dead yeast cells break down and release all sorts of compounds that interact with the wine.

Released proteins bind with tannins in the wine (getting rid of excess tannins and smoothing the wine), which is why this aging process is more suited for white wine (you don’t want tannins in whites), and less so for red wine (red + tannins = good!).

During lees aging (aka sur lie, aka aging on the lees), it’s common to stir the lees (a process called bâtonnage – more French!). Stirring the lees distributes the compounds throughout the wine for optimal flavor and aroma extraction.

The stirring also helps prevent sulfur flavors and aromas (rotten egg smell) that form if the lees absorb too much of the wine’s oxygen. Stirring the lees is especially important for wine that is aging in stainless steel vessels because oxygen isn’t passing through like it would in wood barrels – wine always needs some oxygen.

Lees aging can occur over a matter of weeks to as long as several years – it depends on the flavor the winemaker is going for, and how long the sulfur flavors and aromas can be avoided.

Wines aged on lees are often described as having a creamy texture and being richer, and the added yeast flavor and aroma is bread-like, toasty or nutty. If aged in oak barrels, the lees will extract additional aroma and flavors from the wood.