The start of fermentation (and its ultimate progress) depends to a large degree on initial temperature. Red ferments are carried out at much higher temperatures than for white in order to extract (dissolve) the phenolics, which is achieved by maceration during and after the fermentation. This dissolution occurs more effectively at higher temperatures.

Temperature has a strong influence on extraction by increasing the breakdown of skin cells and the level of dissolution of the phenolics. Thermovinification (heating the grape crop e.g. to 45°C) was developed to take advantage of this characteristic, but it can produce rather coarse wines with ‘burnt’ aromas.

In standard winemaking, moderate temperatures (25°C) favour primeur style wines; good colour extraction allied to fruity aromas and minimal tannin. Higher temperatures (30°C) extract the tannins required for premium wines capable of long ageing. However, if the temperature goes much above 32ºC, the yeast starts to struggle to survive, and stuck ferments may result. So, even for the warmer red ferments, temperature control is desirable, if not essential.