Lees ageing sur lie
Lees aging – French sur lie – means that after fermentation a wine stays in contact with the spent yeast cells for an extended time instead of being racked off straight away. This yeast is not waste but keeps working: it releases compounds that give the wine texture, stability and protection against oxygen.
So it is less a single intervention than a phase – a deliberate decision to give the wine time on the yeast.
While many cellar steps aim at separating and clarifying, lees aging deliberately keeps the wine in contact with a biologically active environment for longer. Through autolysis – the enzymatic self-degradation of the cells – mannoproteins, polysaccharides and amino acids are gradually released from the yeast cells.
What the yeast does to the wine
These compounds above all change the mouthfeel: the wine seems rounder, fuller, often creamier. The mannoproteins also contribute to stability – they reduce the tendency towards tartrate precipitation and support protein stability. Autolysis usually only becomes noticeable after several months and clearly measurable from about a year; warmth and stirring accelerate it. How strongly all this acts also depends on the ageing vessel.
A distinction is made between coarse and fine lees. The coarse lees – larger solids that settle quickly – are often racked off early because they tend to favour off-flavours; the finer lees stay for the texture-giving part of the lees ageing. Classically this work shows in Muscadet sur lie or in white Burgundies, but increasingly also in structured white wines and some reds.
Protection against oxygen – with a downside
The yeast preferentially binds oxygen and thus acts as a buffer against premature oxidation. This protective effect has a downside, however: if the wine lies too long or too undisturbed, sulphur-containing compounds can gain the upper hand and reductive, unpleasant notes can develop. Stirring the lees – bâtonnage – can counter this and promote texture, but itself introduces some oxygen. It remains a balancing act.
A question of the right moment
More important than sheer duration is how the yeast is handled. The right moment for racking does not depend on the calendar but on whether the lees ageing has done its job – whether additional time still brings the wine together or merely preserves it. Where a wine brings no inner order, the yeast cannot create one either; it can round off edges but cannot add a framework that was never there.
How we see it
For us, lees aging is therefore not a phase of looking away but of observing. It fits our way of working: giving the wine time and reading it along the way, rather than forcing an effect. When it succeeds, the wine does not become louder but more composed.