Control of fermentation temperature is a critically important factor in quality wine making. The proper fermentation temperature is dependent on many factors, the most important of which is the style of wine to be produced.
WHY CONTROL TEMPERATURE?
Fermentation produces heat and can cause the temperature inside the fermenter to rise to unacceptable levels. High fermentation temperatures tend to drive off volatile aromatic compounds and increase alcohol concentrations through evaporation. Alcohol inhibition on yeast growth has a greater effect at high temperatures. Lower fermentation temperatures tend to retain fruit aromas and other volatile aromatics while maintaining a fuller mouthfeel.
Red wines should be fermented between 70-85 °F (21-30 °C). Red wines should be fermented at higher temperatures to allow for better color extraction, tannin extraction, and to limit fruitiness which is undesirable in most red wines.
White wines should be fermented between 45-60 °F (7-15 °C). White wines should be fermented at lower temperatures to preserve volatile aromatics, keep volatile acidity low, and produce a full mouth feel.
METHODS OF TEMPERATURE CONTROL
There are many methods of temperature control with varying levels of efficiency and effectiveness.
Jacketed vessels: Jacketed vessels have jackets that allow circulation of a refrigerated liquid (such as ethylene glycol) over the surface of the vessel. This is the most effective and efficient method of temperature control.
Air Conditioning: Air conditioning a room to the desired temperature can control temperature to a certain extent but is not very efficient or effective. For barrel fermentations on white wines this is the only option for temperature control.
Dripping water over the surface of the fermentation vessel or (for very small scale winemaking) immersing the vessel in a water bath can be effective but is difficult to accurately control and can consume large volumes of water.
After fermentation is complete, the wine should be stored at a constant temperature until bottling. For red wines the temperature should be maintained around 68 °F (20 °C). For white wines the temperature should be maintained around 60 °F (15 °C).