During fermentation

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

In standard wine-making, moderate temperatures (25°C) favor early drinking wines; good color 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 35° C 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.