What Are Lees? A Winemaker's Guide to Sur Lie Aging

Every winter, we rack our red barrels and ask the same question: how clean do we want this wine? That decision turns on what is sitting at the bottom of the barrel, and that sediment is what winemakers call lees.

Racking is simple in concept. You pull the clearer wine off the top of the barrel and leave the heavier material behind. The question that always follows from people on tours and at tastings is, what in the heck are lees, and why would I want anything to do with them?

What Are Lees, Exactly?

Lees are largely spent yeast cells that have finished alcoholic fermentation. When the natural sugar is used up, the yeast falls to the bottom of the vessel and starts to break down. Most of those cells are dead, but not all of them. In wines that go through a secondary malolactic fermentation, you also get spent malolactic bacteria settling out for the same reason: they finished their work and dropped out of solution.

The third component is finely divided grape material. The quality and quantity of that material varies a lot depending on the condition of the grapes when they came in. Frozen fruit, for example, leaves more pulp behind. For most white and rosé wines, we settle the juice and rack it before fermentation specifically to limit how much grape material ends up in the lees.

Sur lie (sir-lee) is French for "on the lees." A wine aged sur lie sits on its own spent yeast for an extended period before bottling.

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Bâtonnage (bat-on-naj) means "stirring with a baton." It is the practice of periodically stirring the lees back up into the wine during sur lie aging.

Friend or Foe

When I was at UC Davis in the late 1970s, we were taught that lees were essentially evil. The sooner you got the wine off them, the better. The thinking was that lees would mask fruit and could encourage off aromas or spoilage. That overly cautious philosophy is not totally wrong, but most modern winemakers have moved past it. Handled with care, lees are one of the best tools we have for adding complexity to both the aroma and the palate.

The trick is knowing which wines benefit and which don't.

How We Use Lees at Brian Carter Cellars

The most common application is extended aging of white wines, particularly Chardonnay, on the lees. The technique pairs naturally with bâtonnage, where we stir the barrels on a regular schedule to keep the lees in suspension. The combination is often called Burgundian winemaking because the practice originated there.

At Brian Carter Cellars we use sur lie aging in a few specific places:

• Array Chardonnay: stirred monthly from the end of fermentation until just before bottling, roughly nine months from November through July.
• Nina's Reserve: extended an additional year, giving us a full 20 months on the lees.
• Oriana: a portion is barrel-fermented in neutral oak followed by about five months of sur lie and bâtonnage. The stainless-fermented portion also rests on its lees for a similar period.
• Abracadabra Rosé: the saignée fraction is fermented in neutral barrels on the lees for mouthfeel.

Sparkling wine is the other classic use case. Méthode champenoise wines age on the lees in the bottle before riddling and disgorgement. Champagne requires a minimum of 12 months for non-vintage and 36 months for vintage. Some houses go a decade or more. The lees contact during that time is a big part of why fine Champagne has that toasted, bready character.

There is a third application, leaving red wine on its lees after malolactic fermentation, that I have tried with mixed results. It can add mouthfeel, but it also raises the risk of hydrogen sulfide. I do not use it regularly.

What Lees Actually Contribute

As the lees break down, they release a range of soluble compounds, mostly derived from the cell walls of the yeast. The main categories are polysaccharides, amino acids, and mannoproteins, which are essentially long-chain sugars combined with proteins.

Those compounds add weight to the palate and a whole register of aromas and flavors: yeasty and bready, cheesy, toasty, nutty, and floral. They also do a few quieter jobs that matter just as much: protecting the wine from oxidation, softening the harsher edge of oak tannin or red wine tannin, and improving overall stability so we need less bentonite for fining. In sparkling wine, lees contact also tightens the mousse, giving you finer and more persistent bubbles.

Tasting Lees in the Glass

The next time you open one of our whites or a sparkling wine, look for those signals. The bready, lightly nutty quality on the finish of Oriana is lees character. The roundness across the mid-palate on Array Chardonnay, that weight that feels almost creamy without any residual sugar, is lees character too. Once you know what you are looking for, you start to see it everywhere.

Brian Carter, Winemaker