Management of dissolved gases when bottling
How can the gases dissolved in wine be managed?
Oxygen dissolution depends on:
-
Temperature: the lower the temperature, the faster the O2 dissolves.
-
The concentration of dissolved O2 in the wine: the lower the wine's oxygen content, the faster the O2 in the air in contact with the wine will dissolve.
-
Handling of the wine: the more wine is handled, the faster the O2 dissolves.
-
Area of contact surface: the greater the area in contact with ambient air, the more oxygen from the air will dissolve.
In general, it is recommended not to exceed 2 to 3 mg/l of dissolved oxygen in the wine after bottling in order to avoid undesirable consumption and oxidation of compounds in the wine. However, oxygen management can be even more rigorous, as is the case with Artemis properties, for example, which set a target of 1 mg/l of total dissolved oxygen.
The management of dissolved gases, i.e. O2 and CO2, is implemented jointly since the quantity of one impacts the other. For example, a wine containing 500 mg/l of CO2 can contain a maximum of 5.4 mg/l of dissolved O2. (For more details see Oxygen management).
Various tools are available to monitor and manage dissolved gas in the wine during the preparation for bottling. First, there are devices to calculate the amount of O2 and/or CO2 dissolved in the wine. These tools are called oximeters and work according to two principles:
-
They have an optical probe and the dissolved O2 content is calculated by the difference between two wavelengths
-
They are equipped with electrodes. In this case, it is the calculation of the wine's oxidation-reduction potential that gives the dissolved O2 concentration.
-
Dissolved CO2 can be measured using a tool called a carbodoser, by degassing and measuring the volume lost. Another technique is to measure the absorption by CO2 of non-dispersive infrared radiation (NDIR) in the gas phase.
Second, there are tools that allow the adjustment of O2 and CO2 concentrations before bottling:
-
Membrane contactors are used to adjust the two gases at the same time.
-
A sintered filtering tube can also be used to achieve this but requires an additional step (a first pass to reduce O2 and then a second one to adjust the CO2 content).
-
A stirring rod connected to the racking vat (the vat into which the wine is pumped for bottling) is used to inject CO2.
The addition of CO2 to wine at bottling helps to protect it from oxygen and therefore from early oxidation. CO2 addition can also intensify a white wine's freshness and acidity, or a red wine's tannic structure.
As an indication, the perception threshold of CO2 in red wine is about 400 mg/l. The perception threshold for white wine is around 800 mg/l. By taking into account the perception threshold and the relationship between CO2 and O2, it is possible to adjust the wine's CO2 concentration in order to reduce oxygen dissolution, while reducing the perception of this gas by the consumer.
At Domaine d'Eugénie, the wines' CO2 is adjusted before bottling.
