Carbonation

The steps

A still wine is made in the usual way.
Carbon dioxide from an outside source is dissolved in the wine under pressure.¹
The wine is bottled. For aerated semi-sparkling wine the container may hold no more than 60 litres.¹

There is no second fermentation, no tirage, no lees ageing and no disgorgement.

How the CO2 is produced and kept

The gas is not produced in the wine at all. EU law defines aerated sparkling wine as wine that, on opening, releases CO2 derived wholly or partly from an addition of that gas.¹ "Partly" means that some CO2 from fermentation may also be present. The gas is held by the bottle and closure, as for any sparkling wine; see CO2 and pressure in the bottle.

Legal rules

EU category	Pressure at 20 °C	Other conditions
Aerated sparkling wine	At least 3 bar¹	From wine without PDO or PGI¹
Aerated semi-sparkling wine	1-2.5 bar¹	Containers of 60 L or less; actual alcohol at least 7% vol, total at least 9% vol¹

For comparison, quality sparkling wine needs at least 3.5 bar, all of it from fermentation.¹ Carbonation is closed to the fermentation-based categories. For sparkling wine and quality sparkling wine, EU rules say the CO2 may come only from the alcoholic fermentation of the cuvée.³ Because aerated sparkling wine must be made from wine without PDO or PGI, it cannot be a protected-appellation wine. The six categories side by side are on EU categories of sparkling wine.

Compared with the other methods

Method	Source of the CO2	Possible EU category
Traditional method, Transfer method	Second fermentation in a bottle²	Sparkling or quality sparkling wine¹
Tank method	Second fermentation in a closed tank³	Sparkling or quality sparkling wine¹
Asti method	Single fermentation of must in autoclave⁴	Quality aromatic sparkling wine¹
Carbonation	Gas wholly or partly added¹	Aerated sparkling or aerated semi-sparkling wine¹

The pair of semi-sparkling categories shows the logic of EU law most clearly. Semi-sparkling wine and aerated semi-sparkling wine share the same pressure range (1-2.5 bar) and the same alcohol minimums (at least 7% vol actual, 9% vol total).¹ The only difference is where the gas comes from: in semi-sparkling wine the pressure is endogenous, from fermentation; in the aerated version it comes wholly or partly from added CO2.¹ The same is true at 3 bar for sparkling wine and aerated sparkling wine.¹

Label wording

Aerated sparkling and aerated semi-sparkling wines must carry "obtained by adding carbon dioxide" or "obtained by adding carbon anhydride", in the same type and size as the category name.² The statement may be left out only when the language of the category name itself makes clear that CO2 was added.² See label terms in EU law.