Champagne disgorgement ('degorgement')
Disgorgement is the process during champagne production where dead yeast deposits, from secondary fermentation in the bottle, are removed and the cork replaced without losing too much of the wine or its dissolved gas.
This is achieved by dipping the bottle into a frozen brine solution which freezes the yeast particles together to form an ice plug. A temporary bottle cap placed on the bottle when it was filled at the start of its maturation (and secondary fermentation) period is removed, allowing the pressure within the bottle to force out the plug of dead yeast cells, which gravity (bottles are stored neck down) and riddling (turning of the bottles) has caused to collect in the bottle's neck.
Inevitably, a little wine is lost during this process and the level in each bottle is topped up with a mixture of wine and cane sugar, known as 'liqueur d'expedition'. The amount of sugar used is dependent on the required sweetness (or dryness) of the finished champagne. This part of the champagne process is known as 'dosage'.
The date of disgorgement - when the post-fermentation yeast is expelled, the dosage added and the bottle sealed with a cork - is considered by many champagne houses an important piece of information to convey to drinkers. They argue that knowing when disgorgement took place allows better assessment of the champagne - something which should be considered alongside that of its vintage.
Prior to disgorgement, champagne matures with the presence of the yeast cells which facilitated the secondary fermentation that carbonated the champagne. After disgorgement champagne is thought by many to mature faster because it no longer has this layer of yeast and because the disgorgement process introduces a small amount of fresh oxygen to the bottle which, coupled with the natural properties of cork rather than the temporary cap, allows the wine to 'breathe'.
Proponents of a prolonged maturation period post-disgorgement say that this oxidisation heightens nutty and toasty flavours in the champagne. They also argue that longer post-disgorgement periods better allow the 'liqueur d'expedition' to integrate, so producing a more harmonious wine.
Different champagne houses believe in various minimum maturation periods after disgorgement, but 3-6 months for non-vintage champagnes and 6-12 months for vintage champagnes are not too far wide of the mark. However, 4-6 years post-disgorgement cellar-aging is not uncommon for great vintage champagnes and it is argued that such lengthy periods are necessary for complex spice flavours to emerge.