PRODUCTION OF SPARKLING WINES IN CLOSED VATS     

Click to see the outline operation

1.    FIRST FERMENTATION: grape harvest: numerous varieties are suitable for the closed-vat process; aromatic varieties can also be used, producing very fruity characteristics. preparation of the must: crushing the grapes extracts the must, a fermentable juice which must be clarified by sedimentation before fermentation. first fermentation in vat : the grape sugars are transformed into alcohol and carbon dioxide, the natural fermentation by-product that the winemaker allows to escape to the atmosphere.span>

The first fermentation is generally complete and the still wine obtained is clarified; however, as in the case of Asti produced from Muscat grapes, the fermentation can be interrupted by filtration or cooling: at around 0°C the yeast ceases its activity and deposits at the bottom of the vat; if the fermentation is a long way from complete, the aroma of the fruit still present dominates that of the wine, and the remaining grape sugar provides the desired sweetness for these wines, which are generally dessert wines; in this case there is obviously no second fermentation, the sparkling wine is clarified and bottled under pressure.


2.    SECOND FERMENTATION IN CLOSED VATS UNDER PRESSURE:

preparation of the wine:
yeast is added to the stabilized still wine, together with a small amount of sugar which is destined to provoke the second fermentation; the wine is then put into a closed stainless- or enamelled-steel pressure-resistant vat, maintaining the gas formed during the fermentation dissolved in the wine.

prise de mousse fermentation:
the second fermentation, also known as the prise de mousse, should not be too rapid; it is controlled by regulation of the vat temperature so that it lasts several weeks; the low temperature favours the appearance of fruity and fresh aromas; if the fermentation is taken to completion, when the yeast has consumed all the sugars it begins to partially decompose: this autolysis liberates into the liquid the substances which confer on it that particular aromatic note which makes the difference between a quality sparkling wine and a wine to which gas has simply been added, as in the case of fizzy soft drinks.

clarification: before bottling, yeast residues and other impurities must be removed from the wine:
the wine is cooled, then filtered or centrifuged under pressure and at low temperature in order to eliminate residual yeast and avoid the possible appearance of sediment due to tannins or tartrate crystals during its conservation in bottle; to make the wine sweeter a small amount of liqueur de dosage is added, also called liqueur d’expédition, which is a mixture of grape must or sugar, wine and sometimes brandy.

bottling:
the wine is bottled by isobarometric filling machines operating under carbon dioxide back pressure to avoid frothing, oxygenation and degassing of the wine; the bottle is closed with a mushroom-shaped cork maintained in place by a twisted-wire cage (the muselet), wrapped with a folded aluminium-foil cap;
it is then labelled and cased for shipping.