What are lees in wine?
Essentially, lees are a byproduct of fermentation, during which yeast converts sugar into alcohol and carbon dioxide.
As fermentation comes to an end, the yeast dies and sinks to the bottom. These dead yeast cells, along with other solid particles such as grape skin and insoluble salts, collectively form what we know as lees.
‘Gross lees’ refers to the coarser, heavier sediment that forms in the wine after fermentation. Gross lees tend to naturally fall to the bottom of the winemaking vessel and are generally separated from the liquid quite quickly, although not always.
Fine lees, which winemakers and connoisseurs speak about more often, are smaller particles that settle more slowly in the wine. While they can be filtered out, some winemakers choose to leave them in for varying periods to enhance the wine’s complexity and weight.
Some winemakers might stir the lees to encourage the development of extra texture and aromas in their wines – a method also known as bâtonnage in French.
What does ‘aged on lees’ mean?
Leaving wine in contact with dead yeast cells might not sound too appealing on paper, but lees ageing can be used to develop certain aromas or add more body and texture to wines when winemakers deem it necessary.
The main reason for the texture change is that dead yeast cells decompose naturally or ‘autolyse’, releasing mannoproteins that enrich the wine’s mouthfeel. At the same time, the nutrients in the lees can support malolactic fermentation, during which the sharper malic acid is converted into softer lactic acid, imparting creamier flavour profiles.
This technique is particularly useful when a white wine or a base wine for sparkling wine is relatively lean and simple – given that isn’t the intended style – if the lees are filtered out immediately.
How long does it take?
Depending on the producer’s preferred style, lees contact can last anywhere from a few weeks to several years.
By law, a non-vintage Champagne must be aged for 15 months in bottle and spend at least 12 months on lees, according to the Comité Champagne.
A vintage Champagne must be aged on lees for three years minimum, although in reality many houses age wines for longer than this baseline threshold.
A Cava de Paraje Calificado (the premium terroir-oriented category of Cava) also requires 36 months of lees aging. A ‘Riserve’ Franciacorta need to be aged on lees for at least 60 months.
Some traditional method sparkling wines produced in other part of the world (such as many English sparkling wines) may not have such strict ageing regulations, but producers often value extended lees ageing and may highlight this information on the back label.
Can you taste lees in wine?
In her latest recommendation piece on Muscadet, Decanter’s Natalie Earl described Domaine de la Pépière’s Briords Cuvée Vieilles Vignes Sur Lie 2022 as ‘silky, with some weight and a crème pâtissière richness, followed by a soft-cotton mouthfeel’ – a vivid depiction of the impact of lees ageing (or Sur Lie in French) on a still white wine.
With traditional method sparkling wines, like Champagne, autolysis of yeast cells happens in bottle during second fermentation.
Lees ‘give the wine its complexity and add finesse to the bubbles’, according to the Union of Champagne Houses.
We can taste the ‘autolytic’ flavours such as brioche, biscuit or bread in the finished sparkling wine. Almond, hay and yeasty flavours can also be associated with a wine spending some time aged on lees.
Meanwhile, lees help limit oxidation and create a generally reductive environment for wines to develop.
Therefore, extended lees ageing in bottle for sparkling wines (i.e. late disgorgement) is sometimes associated with greater ageing potential and more complex aromas, while also helping to preserve freshness for longer.
The richness and extra texture from lees contact can also contribute to the overall balance of a wine.
This is especially true for cool-climate English sparkling wines, as their base wines tend to have spiky acidity and a linear, mineral profile, often benefiting significantly from lees ageing to enhance texture and make them more palatable.
Deciding whether to leave a wine ageing or resting on lees, versus actively stirring the lees, often comes down to the stylistic choice of the winery, said Jean-Charles Thomas, winemaking director at Louis Latour in Burgundy, in a Decanter article in 2017.
