Making sparkling wine

New Year's Eve or a wedding are almost unthinkable without a bottle of bubbly. However, whereas still wine has been with us for thousands of years, sparkling wine is a relatively recent phenomenon. For both the discovery and production of sparkling wine were (and remain) dependent on a relatively recent technological innovation – the glass bottle.

The Traditional Method

All Champagnes and most other quality sparkling wines such as Cava and Crémants de Bourgogne and Loire are made using the "traditional" method. This means it starts life as a still "base wine", a relatively light wine with quite high acidity (easily achieved in the northerly, relatively cool Champagne region). The traditional grape varieties used in Champagne are Chardonnay, Pinot Noir and Pinot Meunier – the latter two being black grapes pressed gently to produce a white juice.

The sparkle is the result of a second fermentation (the prise de mousse in French), which takes place in the bottle. The base wine is bottled along with a dose of sugar syrup and yeast, which restarts the fermentation process. As well as a small amount of additional alcohol, the other by-product of this fermentation is carbon dioxide. The gas cannot escape and permeates the wine.

After this fermentation has completed the wine is left to mature. This is very important in softening and adding complexity, and the top Champagnes will spend several years in the cellars. The fermentation process produces sediment, known as the lees, which adds to the complexity and flavour of the wine as it slowly matures.

Finishing

To prepare the sparkling wine for the market, the bottles are gently "riddled", a process of regularly turning and gently upending them to slowly coax the sediment into the neck of the bottle. Traditionally this process was carried out by hand, with bottles placed in special racks, but nowadays is usually performed by a mechanised "gyropalette". A cellar full of robotic cages full of Champagne makes a strange sight indeed.

The final stage of the process is known as disgorgement. The necks of the bottles are plunged into a freezing solution to form a solid plug containing the sediment. The crown cap is then released, and the frozen block of sediment is forced out by the pressure in the bottle. The bottle is topped up by the dosage, a mixture of wine and sugar syrup, and finally has its familiar cork put in place, secured with a wire fastening.

The dosage is important in shaping the final style of the sparkling wine. Only a very few Extra Brut sparkling wines have no dosage at all and these taste very austere. Brut sparkling wines, which taste dry, have up to 15g of sugar per litre. This sugar works to balance the acidity of the original wine and the "drying" character of the fizz.

Blends and Vintages

Most sparkling wines are non-vintage, non-varietal products; the base wine will be made from a blend of varieties, and include a proportion of "reserve" wines from older vintages, helping producers achieve a consistent style. Even such a prestigious Champagne as Krug is a non-vintage blend. However, the finest Champagnes and sparkling wines are usually the product of a single vintage, often only made in good years.

Other Methods

Some sparkling wines (usually considerably cheaper products) use modern variations on the process, designed to reduce the time and expense necessary to produce sparkling wines.

The "transfer method" removes the need for riddling and disgorgement by transferring wine from one bottle to another via a tank, which filters away the sediment. The "tank method" is even further removed from tradition in that the wine is made sparkling in a giant pressurised tank. These process work well and are cost effective, but don't add the complexities of flavour of the traditional method.