What happens during pro-longed ageing of wines on-lees in a bottle?

Under the ‘traditional method’ of sparkling wine production, the second fermentation, which produces the bubbles, must take place in a bottle (as opposed to in a tank).    Depending on the temperature, yeast and the wine, this secondary fermentation can take between 1 and 6 months.   Once the yeast have converted all the sugar into alcohol and carbon dioxide, they die and start to break down in a process called ‘autolysis’.

This process releases compounds into the wine such as mannoproteins and polysaccharides which  interact with compounds already there. The effect is diverse and complex and changes both the mouthfeel and the aroma profile of the wine.  The new aromas we perceive as a result of this are often referred to as the tertiary aromas (the primary being those coming from the grape juice itself, the secondary being those created during active fermentation) and are typified by notes of brioche, fresh toast, honey, baked apples, biscuit and pastry.   The dead yeast cells are called ‘lees’, hence the term ‘on-lees’ ageing as the wine is in contact with the lees all the time.

The unique environment of ageing wine on its lees within the small confines of a bottle with a crown cap has a distinctive impact that cannot be replicated in tank or barrel.   The large surface area/ratio of wine to yeast lees and the very slow ingress of oxygen through the crown cap is unique to bottle ageing.

The legal requirement in champagne is for wine to mature for a minimum of 15 months ‘on lees’ to ensure the development of these unique bottle-aged characters.  However, for many of our wines we believe they benefit from longer than this although a lot depends on house-style and the wine itself.

As a natural product, all wines will evolve and change over time.   Generally, up to a certain point, quality will be judged to improve with time, then plateau and then decline.   No wine lasts for ever and many decline quite rapidly.   Certain attributes in a wine allow it to age longer without spoilage and oxidation (e.g. low pH/high acidity).    But the optimum time to release a wine can only be judged by tasting and experience.

After about 3 years the all the yeast cells are completely broken down so the impact of change is slower and more subtle.   But wines still evolve.

We try not to set hard and fast rules and treat each wine as an individual.   We are not a factory trying to produce an identical product every harvest every year but a boutique producer, guided by nature, the grapes and the wine in bottle.    So we taste each wine and release it when we believe it has hit its optimum profile.   We may not get this right every time, but with experience we are getting better at it!

We are particularly happy with the recently released Blanc de Noirs 2106 which has undergone 5 years maturation on its lees (far longer than most English sparkling wines).   We think it’s a fine example of what ‘traditional method’ wines are all about.