The process of making sparkling wine in sealed tanks in Italy is generally known as metodo charmat normally, refermentation on the lees lasts from two to four weeks.
In recent times, a method known as charmat lungo has been devised, mainly for sparkling wines from Chardonnay and Pinot. This "long" process leaves the wine in contact with the lees in the tank for three months to a year to duplicate some of the effects of the classic method. Both variations 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 cool temperatures under pressure of about 7 to 8 atmospheres.
Isobaric filtration When refermentation is complete, the wine is separated from the lees by passing through a filter into another tank under equal (isobaric) pressure.
Stabilization The wine is stabilized by being chilled to below freezing to precipitate tartaric acid crystals, which are removed.
Isobaric bottling. The isobaric principle is used to maintain steady pressure in the wine as it is bottled and sealed with a cork.
Wines made by the tank-fermentation method are usually sold soon after bottling, though some charmat lungo wines seem to gain harmony after a few months of storage.
Most of Italy's dry or semisweet sparkling wines are made this way. Asti Spumante is an exception, since it undergoes a single fermentation in tanks under a process that maintains its delicate sweetness and the unique fragrance of Moscato grapes.
