Sur lie ageing: what every sommelier should know

The short answer: lees are the sediment left after fermentation, mostly dead yeast cells. Ageing a wine sur lie, on its lees, gives a rounder, creamier texture, can add bread, brioche and nutty notes, and helps keep the wine fresh. Muscadet, white Burgundy and Champagne are the classic examples.

What lees are

• Gross lees: the heavy sediment that drops soon after fermentation, with bits of grape as well as yeast. Usually racked off.
• Fine lees: the finer, mostly yeast sediment. This is what wines are aged on.
• Autolysis: as dead yeast cells break down, they release proteins, polysaccharides and other compounds into the wine. Over time these bring texture and bready, toasty flavours.

What time on the lees does

• Texture: rounder, creamier, fuller in the mouth.
• Aroma: bread, brioche and biscuit with long ageing, sometimes almond or hazelnut.
• Freshness: lees take up oxygen, which helps protect the wine from oxidising.
• Less butter: in Chardonnay, lees contact lowers the buttery diacetyl made during malolactic fermentation.
• A risk: left alone too long, lees can give reductive, sulfur smells such as struck match or rotten egg. Winemakers taste and stir.

Bâtonnage: stirring the lees

Bâtonnage means stirring the lees back into the wine with a stick (bâton), traditionally in the barrels of Burgundy. It increases contact, builds texture and helps keep reductive smells away. Like any seasoning, it can be overdone, leaving a wine heavy rather than fresh.

The classic examples

• Muscadet sur lie, Loire Valley. The grape is Melon de Bourgogne. Under the appellation rules, Muscadet Sèvre et Maine rests on its fine lees from the end of fermentation until at least 1 March after the harvest. For the words sur lie, the wine spends only one winter in vat or barrel and is still on its fine lees when bottled. That keeps it fresh, sometimes with a light prickle. The crus communaux, such as Clisson, Gorges and Le Pallet, rest on their lees much longer. Growers such as Domaine de la Pépière show how good it can be.
• White Burgundy and barrel-aged Chardonnay. Fermented and aged in barrel on the lees, often with bâtonnage.
• Champagne and other traditional-method sparkling wine. After the second fermentation in bottle, the dead yeast stays in the bottle with the wine. Champagne must age at least 15 months in the cellar before release, and vintage Champagne at least three years; most houses age longer. This is where brioche and toast come from.

How to recognise it in the glass

• A creamy, round texture without obvious oak.
• Bread, brioche, biscuit or nutty notes, strongest in long-aged sparkling wine.
• A light spritz in a young Muscadet sur lie.
• Context helps: know which regions and producers use lees ageing, and taste them side by side with wines that don't.

How to sell it at the table

• Describe the texture, not the chemistry: “rounder and creamier, but still fresh.”
• Tell one line of story: “This wine rested on its yeast through the winter before it was bottled.” Sell the feeling, not the science lesson.
• Pair it well: Muscadet sur lie with oysters and shellfish; lees-aged white Burgundy with chicken in a cream sauce or lobster; older Champagne with mushrooms, roast chicken or hard cheese.

Related: malolactic fermentation in Chardonnay, the world's wine barrels and why Champagne ages so well in magnums.

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