The bubbles form because of secondary bottle fermentation. It is another important step of making sparkling classic method wine. The base wine develops carbon dioxide, which is where the perlage comes from; the bubbles form when Trentodoc is poured into the glass.
WAITING TO DEVELOP THE BUBBLES
While the wine is resting, the yeasts and sugars (liqueur de tirage) initiate the secondary fermentation with the production of carbon dioxide and ethyl alcohol. Classic method sparkling wines can be described as “wines that undergo re-fermentation in the bottle.”
The bubbles are formed, a process called the “presa di spuma,” over a period of about 60 days, during which time the pressure in the bottle builds to about 6 atmospheres.
The regulations clearly state the minimum time a Trentodoc must rest on its lees: 15 months for a non-vintage, 24 months for a millesimato, and up to 36 months for a riserva.
The long rest, which winemakers often prolong for months beyond minimum requirements, is what gives the final product its qualities. The wines are able to age so well because the diurnal temperature variations of the Trentino territory give the grapes a high acidity, guaranteeing the wines’ capacity for evolving over long rest periods on their lees.