There are two main methods of making sparkling wine, the metodo champenoise of bottle fermentation, known as metodo classico in Italian, and the closed tank fermentation method, often referred to as metodo charmat.

Bottle fermentation: metodo champenoise
This method of refermentation in bottle consists in the following phases:
Assembling the base wine
The base wine is a blend or cuvée generally made from the varieties Chardonnay and Pinot Nero (in France Pinot Meuuier is also used) using early picked grapes to retain high acidity.
Tirage
This wine is then bottled, with the addition of the liqueur de tirage, a syrupy solution that includes cane sugar and selected yeasts.
Refermentation
After being sealed with metal caps, bottles are shaken and stacked horizontally in a cellar at a constant temperature of 100-120C. Over the next four to five months the yeasts create a gradual refermentation in the wine which transforms the sugar into alcohol, adding one or two degrees to the total alcohol content, and carbon dioxide. At the end of the process the gas will have built up a pressure of 5-6 atmospheres in the bottle.
Ageing on the lees
The wine must now age for approximately another two years. During this period the yeast cells break down in a process known as autolysis, creating a sediment in the bottle. Bottles are re-stacked every six months or so to check for breakage and shaken vigorously (a practice called coup de poignet in French) to prevent the deposit sticking to the side of the glass.
Riddling
Once ageing is complete, the sediment must be removed from the bottle. The first step is riddling, or remuage, in which bottles are placed top down at a 45-degree angle in the slots of hinged A - frame racks known as pupitres. Over the next two months each bottle is skilfully twisted by hand an eighth of its circumference per day to work the deposit down to the neck. The bottles are gradually up-ended in the pupitres until they stand upright in the slots and the deposit rests against the cap.
Removing the sediment
The next step is the dégorgement (sboccatura in Italian). This involves freezing the deposit by inserting the neck of the inverted bottle in a chilled saline solution. The cap is then removed and the pressure of carbon dioxide in the bottle forces out the plug of frozen sediment.
Topping up
The small amount of wine which is lost during the removal of the sediment must now be replaced. Most types of spumante classico are topped up with a solution of mature wine, sugar and acquavit called the liqueur d' expedition, a solution of older wine and cane sugar.

Spumanti are classified according to their level of residual sugar, using the following terms:
Pas Dosé: refers to spumanti topped up with the same wine, without sugar.
The driest type.
Brut: refers to wines with a maximum of 15 g/l of residual sugar.
Extra dry: has 12-20 g/l
Secco: has 17-35 g/l
Semi-secco: has 33-50 g/l
Dolce: has over 50 g/l
Bottles are then sealed with the familiar mushroom shape cork which is anchored with wire bailing to withstand the considerable pressure from inside the bottle.
Bottles are stored for a time so that the liqueur becomes amalgamated with the wine. On average it takes about three years to produce a fine, bottle-fermented spumante.

Tank fermentation: metodo charmat
The process of making sparkling wine in sealed tanks in Italy is generally known as metodo charmat. There are two basic systems:
Charmat corto (short)
Is used mainly with aromatic grape varieties such as prosecco and moscato. The wine referments on the lees for a period lasting two to four weeks.
Charmat lungo (long)
Is suited to chardonnay and pinot nero. The period of refermentation on the lees lasts from three to twelve months.
Both methods are based on the following procedures:
Refermentation
The base wines blended with selected yeasts and sugar are placed in large, stainless steel tanks known as autoclavi, where refermentation takes place at a temperature of 120-130C under pressure of around 7-8 atmospheres.
Isobaric filtration
When refermentation is complete, the wine is separated from the lees by passing through a filter unto another tank under equal (isobaric) pressure.
Stabilization
The wine is stabilized by being chilled down to - 40C. This causes tartaric acid to precipitate in the form of crystals which are then removed.
Isobaric bottling
The isobaric principle is used to maintain constant pressure in the wine as it is bottled and corked.
Wines made by the tank fermantation method are usually released soon after bottling, though some charmat lungo wines seem to gain harmony after a few months of cellaring.