Traditional method: Disgorgement and dosage

The final stage in a complicated production process—though it may be shorter than, say, that of a fine oak-aged red—is to remove the deposit now in the neck of an inverted bottle. The conventional way of achieving this is to freeze the bottle neck and deposit by plunging the necks of the inverted bottles into a tray of freezing solution. The bottles are then upended, the crown cap flipped off, and the 2 cm deposit flies out as a solid pellet of ice. Bottles are then topped up with a mixture of wine and sugar syrup, the so-called dosage, stoppered with a proper champagne cork held on with a wire muzzle, and prepared for labelling. Many of the bigger producers employ a technique known as jetting, long familiar to brewers, to protect the wine from oxidation: just before the cork is inserted, a small dose of wine, or bisulfite diluted in water, is injected into the neck of the bottle at high pressure; this creates bubbles that rise just to the lip of the bottle, pushing out any oxygen in the head space. Most dry sparkling wine is sweetened so that it contains between 5 and 12 g/l residual sugar, the higher the natural acidity of the wine, the more dosage is generally required to counterbalance it, although the longer a wine is aged on lees, the less dosage it needs. One of the apparent effects of climate change seems to be a noticeable trend to reduce the amount of sugar added as grapes are picked riper, with lower acidity.