The bubbles that make sparkling wine so attractive are a natural byproduct of the fermentation process. When grape juice is fermented, the sugar is converted into alcohol and carbon dioxide gas. If the gas cannot escape because the wine is in a sealed tank or bottle, it remains dissolved in the wine—and then when the lid or cork is removed, the gas is released in the form of bubbles. Examples of popular sparkling wines include: Champagne (France), Cava (Spain), Espumante (Portugal), Asti (Italy), Prosecco (Italy) and Sekt (Germany).
Sparkling wine starts its life the same way all other wines do: grapes are pressed and the juice is fermented, creating still wine. Then the still wine undergoes one of the following four processes to infuse it with gas, creating those wonderful, magical bubbles…
This is the traditional method used in France’s Champagne region. It involves a second fermentation in the bottle. While the still wine is in the tank, a mixture of sugar and yeast (liquer de tirage) is added and then the wine is bottled. Each bottle is usually capped with a crown cap or a cork secured with a metal clasp. The bottles are then stored on their sides in a cool environment, such as a cellar or underground cave. Over time, the liquer de tirage causes a second fermentation. All of the additional sugar is converted to alcohol and carbon dioxide is produced.
The bottles remain in storage on their sides for many more months, and the yeast cells from the second fermentation form sediment. A series of steps known as riddling (reumuage) are undertaken to maneuver the sediment into one lump in the bottle and then the bottle is opened and the sediment is removed. This is known as disgorging (dégorgement). While the bottle is open, a small amount of wine and liquid sugar (the final dosage) is added to the bottle before inserting the cork.
The Transfer Method
This method is similar to the Méthode Champenoise up to and including the second fermentation in a bottle. However, in an effort to save time, money and labor, the sediment is removed from the wine by transferring it under pressure to a tank and conveying it through a pressurized filtration system. Then the wine is bottled for sale.
The Charmat Process (aka Tank Method or Cuve Close)
Under this method, the second fermentation happens in a large tank as opposed to a bottle. Still wine is placed in a closed, pressurized tank, and sugar and yeast are added to cause a second fermentation. The sparkling wine is then filtered and bottled under pressure.
Under this method, carbon dioxide is injected directly into still wine to create bubbles.