The grape sugars are converted into alcohol.

Thanks to the action of yeasts (naturally occurring or added), the sugars are gradually converted to alcohol, giving off carbon dioxide, which causes the “bubbling” sound regularly heard in the vat room.

The fermentation stage lasts, on average, four to five days. During this period, the winegrower carries out regular checks on :

• the temperature of the must : alcoholic fermentation causes the must to heat up, which is good for extracting the skin compounds, but needs to be controlled so as not to kill the yeasts. The vats are therefore maintained at temperatures of 28°C to 32°C by various internal or external cooling systems,

• the density of the must : as the density decreases regularly during fermentation, the conversion process can be followed until completion.

aking measurements in this way helps avoid the fermentation process stopping before it should.