Méthode champenoise is the secondary, inside-the-bottle fermentation that is used to create authentic Champagne and other high quality sparkling wines, as well as some Belgian beers, and English ciders. It's what creates the bubbles in the finest sparkling wines, but it is an expensive, labour-intensive process. (Cheaper sparkling wines are made by the Charmat process which involves bulk fermentation in stainless steel vats and bottling under pressure, producing coarser bubbles.)
The EU has declared that this term can only be used in connection with wines from the Champagne region of France. The new EU approved term is Traditional Method.
The pure juice is fermented and matured in oak casks using natural wild yeasts.
After approximately six months the fermentation ceases. The cider is then mixed with a special champagne yeast and a measured amount of cane sugar. Champagne yeast is used due to the granular shape and non-clumping nature of the yeast cells, rather than the usual 'sticky' nature of most yeasts. The mixture is then transferred into full strength champagne bottles (minimum of 900g in weight) where a secondary fermentation takes place after being sealed with a metal crown cap, as used on beer bottles.
The bottles are then stored horizontally at a low constant temperature for a year.
The secondary fermentation makes the cider sparkling with a profusion of tiny bubbles; as the gas pressure builds up in the bottle, the CO2 has only one place to go - into suspension within the liquid. To do this and achieve the target of fine bubbles requires very high gas pressures, hence the need for the correct type of bottle. The taste of the cider also assumes some of the characteristics of a classic wine based champagne. This is due to the breaking down or “autolysis” of the yeast and only occurs if the cider is left on the “lees” for a long period.
The sediment produced during the secondary fermentation is removed by an ingenious method. The bottles are gradually inverted thereby getting the sediment to settle onto the cap. This is where the granular nature of the yeast cells allows them to slide down the inside of the bottle neck for later removal. To do this, an ingenious rack called a “pupitre” is used to hold the bottles as they are gradually turned and tilted upright. The process of giving the bottles a half twist (every day for about a month) to encourage the yeast cells to fall onto the cap is called "remuage".
With the bottle still upside down the top inch is frozen, usually (and traditionally) by inverting the neck of the bottle in a solution of ice and salt. The salt causes the temperature of the ice to drop below freezing by quite a margin; this is how salt 'melts' the ice on roads. Here the good heat-conducting properties of the metal crown-cap come into their own, otherwise it would be a very slow process... Then the cap is removed, the frozen “plug” of sediment is forced out by the pressure built up during the secondary fermentation. This is a very tricky manoeuvre, called "degorgement" by the French, that has to be well practised to avoid spraying sediment and cider everywhere.
Any shortfall is immediately replaced by a “dosage” of cider and cane sugar, to the level of “brut” or dry in champagne wine terms.
Finally, a proper champagne style cork is inserted and a wire cage (called a muselet) is attached.
The traditional method or “méthode champenoise” is a long, fairly complicated process. Although recently pioneered and resurrected when applied to cider by James Lane from Haslemere, there is evidence that secondary in-bottle fermentation began, not in Champagne, but with ciders in the Forest of Dean in the 17th century. This type of cider was held in high esteem in many quarters, and was often the preferred alternative to French wines.