Wine Arcana

Concept

Lees aging

Also known as Sur lie aging, Ageing on lees

Lees aging, or sur lie aging, means keeping wine in contact with sediment formed during or after fermentation. That sediment can include yeast and bacteria, grape fragments, precipitated tartrates, proteins, and material added during clarification. Yeast cells can bind wine compounds, consume some dissolved oxygen, and gradually release cell-wall and intracellular material as they break down.

Which deposit is retained, for how long, in what vessel, and whether it is stirred can change texture, aroma development, oxygen exposure, and stability. Conditions differ between still and traditional-method sparkling wine.

Gross and fine lees

Winemakers distinguish gross and fine lees by how they settle. Gross lees are the heavier deposit that falls quickly after pressing or fermentation. They commonly contain more grape pulp, skin and seed fragments, precipitated solids, and microorganisms. Fine lees are the smaller particles that settle more slowly or remain suspended longer; in a well-clarified wine they may consist predominantly of yeast cells. A racking separates wine from the first deposit, but where one winemaker draws the cut between gross and fine lees may differ from another's.

Still wines intended for extended lees aging are commonly racked away from the gross fraction and kept with selected, sound fine lees. The fruit's condition, fermentation health, microbial population, temperature, and depth of the deposit all affect the risk of unwanted sulfurous or microbial character. Both fractions need monitoring.

What contact time changes

After yeast dies, its own enzymes slowly dismantle the cell, a process called autolysis. Mannoproteins and other polysaccharides from the cell wall, together with peptides, amino acids, lipids, and aroma precursors, can then enter the wine. Release depends on yeast strain, temperature, wine composition, the amount and age of the lees, and how often they are resuspended. Longer contact allows more change, but the effect is neither immediate nor linear.

Yeast-derived polysaccharides can alter the wine's colloidal behaviour and its interactions with tannin. This may make texture seem fuller or less astringent, especially in a white wine with little phenolic weight of its own. Some mannoprotein fractions can also inhibit potassium bitartrate crystallization or reduce the tendency of white wine proteins to form haze. Lees aging may therefore assist tartrate stability or protein stability. Testing determines whether cold treatment, fining, or filtration is also needed.

Lees can adsorb some volatile compounds and later release others; autolysis supplies precursors, while esters, aldehydes, sulfur compounds, and the underlying wine continue to evolve. The result may shift away from fresh fermentation aroma toward more mature or savoury impressions, but it can also mute fruit or expose a fault.

Stirring, oxygen, and risk

Stirring the deposit back into a still wine is called bâtonnage. It increases contact between the wine and yeast material and can accelerate the transfer of lees-derived compounds. A winemaker can stir frequently, occasionally, or not at all, then rack when the intended balance is reached. Stirring changes the distribution of solids, turbidity, and redox conditions as well as the rate of contact.

Opening a barrel and moving its contents can admit oxygen. Suspended yeast lees can consume part of that dissolved oxygen, and released compounds can also contribute reducing capacity, but this protection is limited and variable. In a study of commercial white wines, yeast lees consumed anywhere from none to 47 percent of the dissolved oxygen under the trial conditions; chemical oxidation proceeded at the same time.1. Volker Schneider, Jonas Müller & Dominik Schmidt, “Oxygen Consumption by Postfermentation Wine Yeast Lees: Factors Affecting Its Rate and Extent under Oenological Conditions,” Food Technology and Biotechnology 54 (2016), pp. 395–402, https://doi.org/10.17113/ftb.54.04.16.4651. Yeast strain, lees quantity and age, temperature, sulfur dioxide, vessel, headspace, and stirring technique all matter.

The opposite risk is an excessively reducing, compact deposit that favours unwanted volatile sulfur compounds. Resuspension may help a winemaker manage that environment, but it can also distribute unsound lees or nutrients useful to spoilage organisms. Tasting, analysis, topping, temperature control, and timely racking remain part of lees management.

Still and traditional-method sparkling wine

In still wine, the relevant lees usually follow the primary alcoholic fermentation. The winemaker can separate coarse solids, choose tank or barrel, retain or transfer fine lees, stir them, and end contact by racking or filtration. Malolactic fermentation may overlap with this period. Vessel permeability and repeated cellar operations can make oxygen management central to the result.

In traditional-method sparkling wine, a clarified still base wine undergoes a second fermentation in its sealed final bottle. The resulting deposit is principally the yeast of that second fermentation, sometimes with a riddling aid. Each bottle then matures under carbon dioxide pressure, generally cool and closed, without routine bâtonnage. Riddling eventually gathers the sediment at the neck; disgorgement removes it and ends lees contact.

Those conditions give time a different role. Autolysis can affect texture, aroma precursors, foam, and the way carbon dioxide is perceived, while the base wine also ages in a relatively protected bottle. A controlled 24-month study of Chardonnay and Pinot Noir found that age and base wine composition explained much of the aroma development, with some wines aged without lees developing similarly to their sparkling counterparts.2. S. Sawyer et al., “Autolysis and the duration of ageing on lees independently influence the aroma composition of traditional method sparkling wine,” Australian Journal of Grape and Wine Research 28 (2022), pp. 146–159, https://doi.org/10.1111/ajgw.12527. Longer bottle aging can permit further autolysis, but grape, base-wine production, yeast, temperature, closure, and oxygen remain consequential.

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