Champagne's traditional method: how yeast autolysis shapes foam and aroma

Tirage and the second fermentation in the bottle

In the traditional method, a still base wine becomes sparkling through a second alcoholic fermentation inside the bottle. A liqueur de tirage of sugar and yeast is added, the bottle is sealed, and the yeast ferments the sugar into alcohol and carbon dioxide. Because the bottle is closed, the gas cannot escape and stays dissolved in the wine.

EU law reserves the term 'traditional method' for wines made sparkling by a second alcoholic fermentation in the bottle, kept in contact with the lees without interruption for at least 9 months in the same undertaking from the time the cuvée was made up, and then separated from the lees by disgorging. For a quality sparkling wine, EU rules also require an excess pressure of at least 3.5 bar at 20 °C in a closed container.

When the yeast dies: what autolysis is

Once the sugar has been used up, the yeast stops fermenting, settles as lees and gradually dies. Autolysis then begins: enzymes inside the dead cells, such as proteases and glucanases, break down the cells' proteins, walls and other components, and the breakdown products pass into the wine.

In wine the process is slow. Low pH, alcohol and cool cellar temperatures hold the enzymes back, so the effects of autolysis build up over months and years on the lees rather than over days. That is why the length of time on the lees weighs so heavily on the style of a traditional-method wine.

What autolysis releases: foam, texture and aroma

The breakdown of the cell walls releases polysaccharides, above all mannoproteins. Research links these molecules to the stability of the foam and to a rounder mouthfeel, which is one reason lees ageing is valued in sparkling wine.

The breakdown of proteins releases peptides and amino acids, and nucleic-acid products and lipids are released as well. Nucleotides from the nucleic acids may affect flavour, and the effect of lipids on foam has been studied with mixed results. Some of these compounds can act as precursors of aroma. The toasty, brioche-like and nutty notes often described in wines aged long on their lees are associated with these changes, but the exact chemical pathways are still being studied and cannot be reduced to a single reaction.

Time on the lees: what the rules fix

The EU minimum of 9 months on the lees is a condition for using the term 'traditional method'. Appellation specifications can require longer periods. In Champagne, a non-vintage wine must mature for at least 15 months from tirage, at least 12 of them on the lees, and a vintage wine for at least three years.

Because autolysis is slow, a longer time on the lees gives it more time to work. How long a producer waits beyond the legal minimum is therefore a choice of style.

Riddling, disgorging and dosage

Before the wine is released, the lees have to leave the bottle. Riddling turns and tilts the bottles step by step until the deposit has slid into the neck, and disgorging then removes it. In the EU rules for the 'traditional method', disgorging is named as the way the wine is separated from its lees.

After disgorging comes the dosage: a small addition of liqueur that sets the final sweetness. EU labelling terms are defined by sugar content: Brut Nature means under 3 g/L and may be used only when no sugar has been added after the second fermentation, Extra Brut means 0 to 6 g/L, and Brut means under 12 g/L.

Chalk and climate behind the base wine

The region's climate is shaped by both maritime and continental influences, with an average annual temperature of about 11 °C. This climate is linked to grapes with a subtle balance of acidity and sugar.

Where the subsoil is chalk, it can hold 300 to 400 litres of water per cubic metre and act as a water reservoir for the vines. Elevation and slope aspect differ from one vineyard to the next.

Practice question: autolysis and ageing on the lees

Question
Explain how yeast autolysis during ageing on the lees changes a traditional-method sparkling wine. Refer to what is released and to the effects on foam, texture and aroma.

Model answer
After the second fermentation the yeast dies and settles as lees. Its own enzymes, such as proteases and glucanases, slowly break the cells down and release peptides and amino acids, cell-wall polysaccharides such as mannoproteins, nucleic-acid products and lipids. Mannoproteins are linked to foam stability and a rounder mouthfeel; amino acids and other released compounds can act as precursors of toasty, brioche-like aromas. Because autolysis is slow at wine pH, alcohol levels and cellar temperatures, its effects grow with time on the lees; in the EU the term 'traditional method' requires at least 9 months on the lees.

Marking guide (10 points)
- Yeast death and self-digestion by the cell's own enzymes (3 points)
- The compounds released and their links to foam and mouthfeel (3 points)
- Aroma precursors, the slow pace of autolysis and why time on the lees matters, including the EU minimum of 9 months (4 points)