Alcoholic fermentation, which can also sometimes be called ethyl fermentation, is an essential step in wine making. It is this which makes it possible to obtain a more or less alcoholic drink, thanks to the transformation of sugars into alcohol. Let us then go into the details of the alcoholic fermentation process of wines .
The origins of alcoholic fermentation
The process of transforming sugar into alcohol began to be studied in the 17th century, but it was especially during the 20th century that the greatest advances took place. Microbial agents were then used to prepare wine and beer, but also bread, and even vinegar.
However, before we could even put a name to the process, alcoholic fermentation had been used for millennia, without even knowing it, because we find the first traces of wine making more than 10,000 years before our era.
How alcoholic fermentation works
Whether to produce red wines, white wines, rosé wines, or even sparkling wines, the winemaking process follows rigorous stages that ensure the final quality of the drink. Among all the phases of wine making, alcoholic fermentation takes place after settling.
This then consists of transforming the sugars, naturally present in grape juice, into alcohol, thanks to the action of yeasts. The yeasts then absorb the sugars until complete fermentation, and transform them into alcohol. The natural process ends by itself when there is no longer any sugar in the grape juice, but the winemaker can also intervene to stop the fermentation, and thus measure the alcohol level of the wine .
During this crucial stage of winemaking, heat and carbon dioxide (CO2) are released in large quantities.
The other fermentation process
Alcoholic fermentation is undoubtedly the most essential step in producing a quality wine. But there is also another type of fermentation : malolactic fermentation.
Triggered just after alcoholic fermentation, malolactic fermentation consists of transforming malic acid into lactic acid , under the action of lactic acid bacteria. If the first fermentation process then makes it possible to increase the alcohol level of the wine and provide fruity and floral aromas, this second stage offers the wine more sweetness and roundness. The alcoholic drink is then more supple, and the lactic bacteria provide notes of biscuit, brioche or even butter.
Malolactic fermentation is not applied to all wines, and many producers skip this step when making white wines, to preserve the wine's clean qualities. On the other hand, for red wines, this fermentation is particularly important, because it reduces the acidity of the wine .
During malolactic fermentation, carbon dioxide is released, and other components are released, such as glycerol, acetic acid, succinic acid and aromatic components.
The fermentation conditions to be met
The success of alcoholic fermentation depends on several criteria, and it is not enough to place the wine in vats while waiting for the yeasts to play their role. To ensure an optimal process, several points of vigilance must be observed.
Fermentation is an exothermic reaction , meaning heat is released during the biochemical process. It is then necessary to ensure an ideal temperature in the tank to guarantee a quality process. The winemaker must then regularly check this criterion.
If the temperature is too high , fermentation can stop on its own, even before the sugar in the must is completely absorbed. The consequences are even more unfortunate for red wine, which can see its bouquet alter, and give way to an unpleasant herbaceous or bitter taste. As for white wines, too high a temperature can alter the quality and richness of the aromas.
Otherwise, a temperature that is too low risks blocking the start of fermentation , because the yeasts develop too slowly.
To optimize the chemical reaction, the fermentation temperature varies depending on the type of wine:
- 28 to 30 degrees for red wine;
- 18 to 20 degrees for white wine and rosé wine;
- 20 to 22 degrees for sweet wine.
To regulate the temperature during the fermentation process, the winemaker can use the trickling method, which consists of circulating cold or hot water in the double wall of the tank, or use a flag temperature exchanger.
The container and fermentation time
Other criteria to take into account for successful fermentation are the type of tank and the duration of the biological process. In general, oenologists choose to place the wine in a stainless steel vat , more rarely in an oak barrel. Then, the alcoholic fermentation lasts, on average, 2 weeks .
The stages of alcoholic fermentation
For optimal fermentation, a 3-step process must be carried out.
- Pumping over : the fermenting must is returned so that it rises to the surface of the tank. This allows the juice to aerate and provide the yeast with the oxygen they need;
- Yeasting : the addition of special yeasts allows fermentation to be accelerated or restarted, so that the transformation of sugar into alcohol is complete, and the level of residual sugars is as low as possible;
- Optimization of fermentation : this last stage of fermentation consists of checking the exhaustion of sugar, in order to ensure the quality of the wine.
Alexis Cornu: the visionary oenologist of our domain
To produce quality Provence wines, Alexis Cornu, the estate's oenologist, pays particular attention to the different types of fermentation. To develop the new rosé cuvée from Château de Berne , he chose to place part of the blend in wooden barrels for several months . To succeed in this new method of vinifying rosé , several criteria were worked on, from the choice of plots for blending , to the longer maceration time. This makes it possible to obtain a gourmet rosé wine, particularly suited to aging.
Wine production is meticulous work that requires constant vigilance. The alcoholic fermentation stage requires the full attention of the winemaker, a work that we entrust to our oenologist Alexis Cornu, and which allows us to obtain exceptional rosé wines .