Champagne is the usual choice for festive celebrations but there are other sparkling wines that are comparable and of excellent value.
The carbon dioxide that creates the sparkle in your bubbly tends to find its way there in one of two main ways. The méthode champenoise is what's used for champagne and other high-end sparkling wines and involves the wine undergoing a secondary fermentation in the bottle.
A bottle of champagne holds about six bars of atmospheric pressure; four grams of sugar per litre of wine will produce one bar, so 24 grams of sugar per litre - including the residual sugar present in the wine before more is added - are needed for the right level of fizz. Each bottle is first capped and aged on its side to let the sugar and yeast cells do their work. When the ageing is finished, the bottles are gradually inverted until they are upside down (this is called riddling, or remuage in French), whereupon the necks are quickly submerged in a salted ice-water bath and the caps removed. By this process, the sediment from the dead yeast cells is forced out by the pressure of the CO 2 inside the bottle. A small amount of "dosage" - a mixture of wine, brandy and sugar - is added to adjust the final sweetness level of the wine.
Crémant wines offer excellent value as an alternative to champagne. They have a slightly lower level of bubbles (two to three bars of pressure) and, whereas champagne wines are made, in the main, from pinot noir, chardonnay and pinot meunier, crémant can be made with the grapes of other specific regions - Crémant d'Alsace can have a bit of riesling in it; a Crémant de Bordeaux might have sauvignon blanc or sémillon; Crémant de Bourgogne is made from chardonnay, pinot blanc, pinot gris and sometimes a bit of aligoté.
A more economical way of making wine fizzy is the charmat process; it is most popularly used in Italy, to craft prosecco and other sparkling wines such as Asti, which are intended to be consumed young and fresh. The second fermentation occurs in a large stainless-steel tank prior to bottling, rather than in a bottle, resulting in a wine that usually has about 4.5 bars of pressure, which means the bubbles are not as vigorous as they are in a bottle of champagne. With prosecco, bottles labelled "spumante" have lots of bubbles, whereas "frizzante" designates a lightly bubbled style.
Cava from Penedes, in Catalonia, Spain, follows the méthode champenoise, but the grapes are different - macabeu, parellada, xarel-lo, chardonnay, pinot noir and subirat. The result is lots of bubbles at a reasonable price.
There are myriad other interesting sparkling wines out there - too many to cover here, in fact. Honourable mentions go to sekt, from Germany, and English and American sparklers that are modelled on champagne. Australia offers some great examples, too, the most interesting of which are sparkling shiraz wines - a quirky tipple that is either somewhat sweet, or dry and tannic.