Different gases can be used to inert wines:
- Carbon dioxide (CO2)
- Diazote
- Argon
- Carbon dioxide / diazote mixture
Depending on the stage, different gases can be used or are naturally present in the environment.
5.5.2.b Management of dissolved gases
Argon
A noble gas that is entirely inert with regard to wine. It is rarely used because it is very expensive.
Nitrogen
This gas is widely used to inert the vat headspace, for example, but it is rarely dissolved in wine because it tends to temporarily toughen wines, which does not facilitate tasting during ageing.
Carbon dioxide
CO2 is very commonly used because it is inexpensive and very soluble in wine. Yeasts produce this gas during alcoholic fermentation, so it is present in significant quantities early in the vinification process. From an organoleptic point of view, CO2 leads to an overexpression of tannins and acidity when tasted, but stirring is enough to eliminate it from the wine.
The CO2 concentration in the wine impacts the maximum amount of dissolved oxygen. At 20°C, the following relationship can be applied:
Max dissolved O2 in mg/L] = 7.9 mg/L - 0.005 x [Dissolved CO2 in mg/L]
When there is no CO2 in wine, the maximum value of dissolved oxygen in the wine is the standard value, i.e. 7.9 mg/L. However, for 500 mg/L, the maximum amount is 5.4 mg/L.
Below is a table of typical values at 20°C:
| The wine's dissolved CO2 quantity in mg/L | Maximum potential dissolved oxygen |
|---|---|
| 0 | 7,9 |
| 400 | 5,9 |
| 600 | 4,9 |
| 800 | 3,9 |
| 1000 | 2,9 |
| 1200 | 1,9 |
| 1400 | 0,9 |
Based on these figures, it becomes clear that controlling dissolved CO2 can help manage the absorption of oxygen in wine. CO2 is present in high concentrations in the wine following fermentation, with concentrations above 1200 mg/L. So at this point, during barrelling, the wine is protected from excessive oxygen intake.
A first important point is that CO2 does not prevent oxygen dissolution in the wine, but rather decreases the maximum oxygen content at a given time. Similarly, the reactions between wine's compounds and oxygen are not hindered. It therefore avoids excesses but not the addition itself.
Secondly, when the wine is moved, CO2 can easily be released, reducing its concentration. Managing dissolved oxygen with dissolved CO2 alone is difficult but it is an excellent tool for avoiding oxygen saturation.
Furthermore, in the case of sulphite-free ageing, it is beneficial to maintain a fairly high level of dissolved CO2 or even to readjust the dissolved CO2 level during ageing.
Obviously, when the aim is to add oxygen via micro-oxygenation for example, a CO2 concentration that is too high becomes less beneficial and hinders the oxygen's dissolution.