Lees

Gross lees and fine lees

Winemakers distinguish between gross lees, the heavy sediment that falls out of the wine in the first weeks after fermentation, and fine lees, the lighter particles that stay in suspension for longer. Gross lees are usually racked off within a few weeks. Fine lees are deliberately kept in contact with the wine, either in barrel, in tank or in bottle, to add complexity.

Lees ageing in barrel is the classic Burgundian technique, used for premium Chardonnay and Pinot Noir. The wine is stirred, the so-called bâtonnage, every week or two, to keep the lees in suspension and to extract flavour. The autolysis of the dead yeast cells releases mannoproteins, polysaccharides and other compounds that soften the wine and add texture.

Lees in sparkling wine

For traditional method sparkling wine, lees ageing is the defining characteristic. The wine spends 24 to 84 months in bottle, in contact with the dead yeast cells from the second fermentation. The autolysis of those cells, over the long months on the lees, releases a complex array of aroma and flavour compounds, including brioche, baked apple, toasted nut, biscuit and a soft, creamy texture that is the signature of premium sparkling wine.

UK producers take this very seriously. Nyetimber's wines are aged on lees for 36 to 60 months depending on the cuvée, Gusbourne's prestige Fifty One for around 60 months, Hambledon's Première Cuvée for 36 to 48. The English Sparkling PDO sets a minimum of 24 months for non-vintage and 36 months for vintage wines, well above the basic Champagne minimum of 15 months.

How lees ageing is done in the UK

For still wines, lees ageing is usually done in barrel, with the wine topped up regularly to compensate for evaporation. Most UK producers stir the lees every week or two for the first three to six months, then leave the wine to settle. The total time on lees varies from 6 to 18 months depending on the style.

For sparkling wines, the lees ageing is the time between the second fermentation and the disgorgement, typically 24 to 60 months. During this time, the bottles are stored horizontally in a temperature-controlled cellar, often at 12 to 14 degrees Celsius. The bottles are riddled (turned) periodically, either by hand on pupitres or by machine on gyropalettes, to collect the lees in the neck for disgorgement.

What lees ageing adds

The sensory effect is real. Lees-aged wines tend to be more complex on the nose, with bready, yeasty, nutty notes layered over the primary fruit. On the palate, the texture is softer and more integrated, with a creaminess that comes from the mannoproteins released by autolysis. Some lees-aged wines also have a slightly reduced perception of acidity, because the lees buffer the acids.

Beyond flavour, lees ageing also contributes to stability. The mannoproteins can help prevent tartrate crystals from forming in the bottle, and they reduce the wine's sensitivity to protein haze. The net effect is a wine that is more complex, more stable and more ageworthy than the same wine aged off the lees.