4.1.4 Oxygen management from vatting to post-fermentation maceration

What are the risks associated with excess oxygen?

An excessive amount of oxygen at the wrong time can destroy certain desirable aromas such as thiols or terpenes. Vigilance is therefore crucial both before and after alcoholic fermentation. During alcoholic fermentation, the yeasts consume so much oxygen and the environment is so saturated with CO2 that there are no risks, quite the reverse.
On the other hand, too much oxygenation can lead to a gas-like odour produced by an excessive amount of ethanal.

Finally, in an uncontrolled environment, it is possible that acetic bacteria may develop producing volatile acidity.
To overcome such issues it is necessary to:

• Inert with a gas during the pre-fermentation phase using, for example, dry ice
• Inert the pomace cap using nitrogen or CO2 at the end of alcoholic fermentation

What are the risks associated with insufficient oxygen?

There is a lack of oxygen throughout fermentation, the risks are:

• Development of reduction notes
• Production of acetic acid by the yeast.
• Lethargic fermentation

The solution is simple: carry out an aerated pumping over, a rack and return action (délestage) or macro-oxygenation (cliquage) during alcoholic fermentation.