What Is Lees ageing? A Beginner’s Guide

Quick answer: what is lees ageing?

Lees ageing is the practice of holding wine in contact with sediment left from winemaking, usually after fermentation. This sediment often contains yeast cells, but it can also include grape solids, tartrate salts, bacteria and other winemaking residues.

During this contact, yeast cells can gradually break down in a process called autolysis. Compounds released from the cells may influence the wine’s texture, aroma, flavour integration and some stability properties.

The result is not predictable from the phrase alone. Lees composition, contact time, vessel, temperature, oxygen exposure, stirring and the wine itself all matter. In Australia, you may encounter the terms on lees, sur lie, lees aged, lees ageing, lees-stirred and bâtonnage, particularly when reading about Chardonnay or traditional-method sparkling wine.

What are lees?

Lees are solids-containing material that settles out of grape juice or wine. They form as suspended material falls to the bottom of a tank, barrel or bottle during processes such as clarification and fermentation.

It is tempting to define lees as “dead yeast”, but that is too narrow. Yeast may be an important part of fermentation lees, while other lees can contain grape material, tartrate precipitates, fining agents, bacteria or oak material.

Gross lees and fine lees

Winemakers often refer to gross lees and fine lees:

• Gross lees generally means heavier, coarser sediment that settles relatively early.
• Fine lees generally means lighter sediment remaining after heavier solids have been removed, often with a greater proportion of yeast-derived material.

These are useful practical terms, but they are not perfectly standardised. Their composition depends on the grapes, pressing, clarification, yeast, fermentation method and handling decisions.

How does lees ageing work?

A simplified sequence looks like this:

1. Fermentation creates yeast biomass and leaves other solids suspended in the wine.
2. The solids settle at the bottom of the vessel.
3. The winemaker decides whether to remove the sediment, retain some of it or manage different fractions separately.
4. The wine remains in contact with the retained lees for a period of maturation.
5. The lees may be left undisturbed or stirred occasionally.
6. The wine is eventually separated from the lees, clarified, filtered or bottled.

Racking wine away from sediment reduces or ends that contact. Retaining selected lees is therefore a deliberate winemaking decision, not something that happens in exactly the same way with every wine.

Lees ageing versus lees stirring

Lees ageing describes the contact period. Lees stirring describes one way of managing that contact.

Lees stirring, also called bâtonnage, resuspends settled lees so they mix back into the wine. It can increase contact and change how quickly the wine interacts with the sediment. But it is optional: a wine can remain on lees without being stirred.

For a closer explanation of this separate technique, see lees stirring.

Stirring may also change oxygen exposure. That is one reason more stirring does not automatically produce a better result. The frequency, timing and force of stirring all matter.

What can lees ageing do to wine?

Lees contact can contribute to a fuller, rounder or smoother mouthfeel in some wines. Yeast-derived compounds, including mannoproteins and other polysaccharides, may affect the way the wine feels and how some structural elements are perceived.

Lees ageing may also alter the balance between fruit-, oak- and yeast-derived characters. Some wines develop greater aromatic integration or complexity. Descriptors such as bready, biscuity, nutty or yeasty are particularly associated with some sparkling wines and extended yeast contact.

These are possibilities, not guarantees. Lees ageing does not automatically make a wine creamy, bready or more complex. Oak, bottle age, fermentation choices and other factors can contribute similar impressions.

Lees can also affect oxygen management. In some circumstances they can consume oxygen, but stirring, topping and other handling can introduce oxygen. Poorly managed contact may contribute to reductive, sulfurous, cheesy or dirty characters, or to oxidation and other instability.

Where might you encounter it?

Australian learners are especially likely to see lees terminology in descriptions of:

• Australian Chardonnay that has been fermented or matured on lees; and
• Australian traditional-method sparkling wine that has spent time in contact with yeast sediment in bottle.

These are examples of common style contexts, not rules for all Australian Chardonnay or sparkling wine.

In traditional-method sparkling wine, a second fermentation takes place in the bottle. Yeast sediment remains during bottle maturation before riddling and disgorgement. The finished wine’s bready or autolytic character can reflect this lees contact, but it also depends on the base wine, bottle age, dosage, oxygen history and other production choices.

How should you read the label?

• On lees usually means the wine was held in contact with lees.
• Sur lie is French for “on the lees” and is commonly used for wines matured with lees contact.
• Lees-stirred indicates that stirring was used.
• Bâtonnage is another term for lees stirring.

These phrases do not necessarily tell you the lees fraction, exact duration, vessel, stirring schedule or whether all the wine stayed continuously on the same sediment. “Lees-stirred” and “on lees” should not be treated as interchangeable: stirring is one possible technique within lees management.

What lees ageing is not

Lees ageing is separate from:

• Fermentation: fermentation helps create the yeast and sediment, while lees ageing is a later maturation decision.
• Malolactic fermentation: this is a bacterial conversion of malic acid to lactic acid. It may overlap with lees contact, but lees ageing does not automatically cause it.
• Oak or barrel ageing: wine can age on lees in stainless steel, while barrel-aged wine may have little or no lees contact.
• Bottle ageing: wine can mature in bottle without yeast sediment, although traditional-method sparkling wine does combine bottle maturation with lees contact before disgorgement.

You can learn more about the wider sequence in how wine is made, and compare lees contact with racking wine, barrel ageing and bottle ageing.

Common questions

Does lees ageing make wine better?

Not automatically. It is a winemaking choice that can produce desirable texture or integration when well managed, but it can also contribute unwanted sulfurous, cheesy, reductive or oxidative characters.

Does lees ageing mean the wine was stirred?

No. Lees stirring is optional. A wine may be held on lees without bâtonnage.

Does “sur lie” mean a fixed ageing period?

No. “Sur lie” indicates lees contact, but the phrase alone does not specify a universal duration, lees fraction, vessel or stirring regime.

Does lees ageing mean a wine was aged in oak?

No. Lees contact can occur in tank, barrel or bottle. Oak ageing is a separate process and oak flavours should not automatically be attributed to lees.

Can you taste lees ageing?

Sometimes, but not in one single, reliable way. You may notice a fuller texture or greater integration, or in some sparkling wines, bready or yeasty notes. The result varies with the wine and its production choices.