Wine yeasts create different compounds at different temperatures.
Cooler fermentations preserve more aromatic esters and create lean, focused wines, but sometimes with reduced 'mouth feel'.
Warmer fermentations can give greater complexity and mouth feel, but at the loss of the original personality of the grapes.
The warmer a fermentation gets, the higher the amount of H₂S that will be produced.
Ideally we need to be able to control the fermentation temperature within a desired range, for the style we are trying to make, especially not allowing it to get too hot.

During fermentation, a grape must initially at 91 °Oeschle (21.8% Brix = 21.8% sugar) would theoretically generate enough heat to raise the temperature by 28.2 °C;
but up to 20% of this heat is carried away in the CO₂ given off, or lost via the tank walls according to the temperature difference with the cellar room.

White wines during fermentation should be at between 12 °C and 16 °C, so the fermentation lasts for 3 to 6 weeks;
warming may be necessary initially to raise the temperature of juice above 10 °C in order to enable the fermentation to start.
After fermentation they should be kept at a maximum of 16 °C; 13 °C is ideal.

For white wine fermentation to last 28 days, reducing by around 3.25 °Oeschle per day, it is necessary to cool by 0.8 °C to 1 °C per day.
At this rate, 1 kWatt of refrigeration can control about 20,000 litres of liquid.

Red wines during fermentation should be at between 18 °C and 24 °C, so the fermentation lasts for 7 to 14 days;
after fermentation they should be kept at a maximum of 20 °C; 18 °C is ideal.
Above about 18 °C to 20 °C the loss of volatile aromas and flavours occurs more rapidly.

For red wine fermentation to last 10 days, reducing by around 9.1 °Oeschle per day, it is necessary to cool by 2.26 °C to 2.82 °C per day.
At this rate, 1 kWatt of refrigeration can control about 7,000 litres of liquid.

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