Timing of the riddling process after the second fermentation is a key element in quality and style of a traditional method sparkling wine, the second most important factor affecting quality after blending the base wine. The longer a wine rests on the lees of the second fermentation in bottle, the more chance it has of picking up flavour from the dead yeast cells, a process known as yeast autolysis.
Most regulations for traditional method sparkling wines specify at least nine months’ ageing on lees, and the minimum period for non-vintage champagne was increased to 15 months in the early 1990s (vintage champagnes are usually aged for several years). During the bottle ageing process, the yeast cells autolyse, releasing increasingly complex flavour compounds. The chemistry of autolysis is not fully understood, but it seems that autolysis has significant effects only after about 18 months on the lees, and that the most obvious changes occur after five to ten years of lees contact, which inevitably increases production costs considerably. It may be that compulsory periods of lees contact in bottle of only a few months have less effect on quality than has been imagined.