Changing the temperature at different times during a fermentation to aid extraction of colour or tannin is a winemaking technique that is widely used in the production of red wines.
Background
The contribution of grape-derived phenolics to the colour, tannin concentration, overall quality and ageing potential of red wines has been established by numerous studies. While the initial concentration of phenolic compounds in grapes has some relationship to the final phenolic composition of wine, fermentation temperature and the extent and duration of cap management have been shown to strongly influence phenolic extraction during winemaking, and the phenolic composition of wines over time.
Studies on the extraction of phenolics during red winemaking have shown that the maximum extraction of colour occurs before that of tannins, and that maximum colour is obtained earlier at higher temperatures.
Not all phenolics are extracted at the same rate during fermentation, and while the rate of extraction of some compounds increases with increasing fermentation temperature, the final concentrations may be unaffected. For instance, Lerno et al. (2015) found that increased fermentation temperature increased the rate of extraction but not the final concentration of skin-derived phenolics, whereas for seed-derived phenolics both the rate and final concentration increased. It was also concluded that must temperature was more important than cap temperature in determining the extraction of phenolics.
Potential risks
Increased fermentation temperature increases the rate of fermentation, thereby further increasing temperature in a positive feedback loop. Consequently, there is a greater risk of fermentations becoming uncontrollable at higher temperature if insufficient cooling capacity is available or if the fermentations are not actively cooled, and this can result in undesirable sensory characters. Extreme temperatures >35°C, or constant increasing and lowering of fermentation temperature, can also begin to affect yeast health and viability and increase the risk of a stuck fermentation.
Practical and logistical considerations
Pumping the fermenting liquid though a heat exchanger and distributing the cooled liquid over the cap is the most effective way of cooling a ferment. In addition, while pumping over, rack-and-return, and to a lesser degree plunging may all help to dissipate heat, they also introduce oxygen which may stimulate yeast and result in an increased fermentation rate.
Resources
Godden, P. 2021. Ask the AWRI: Effects of fermentation temperature on red wine composition. Aust. N.Z. Grapegrower Winemaker (690): 50-52.
Godden, P. 2021. The effects of fermentation temperature on the composition of red wines. AWRI Technical Review. 252: 13-17.
Lerno, L., Reichwage, M., Ponangi, R., Hearne, L., Block, D. E., Oberholster, A. 2015. Effects of cap and overall temperature on phenolic extraction in Cabernet Sauvignon fermentations. Am. J. Enol. Vitic. 66(4): 444-453.
Ntuli, R.G., Saltman, Y., Ponangi, R., Jeffery, D.W., Bindon, K., Wilkinson, K.L. 2022. Impact of fermentation temperature and grape solids content on the chemical composition and sensory profiles of Cabernet Sauvignon wines made from flash détente treated must fermented off-skins. Food Chem. 369: 130861. doi.org/10.1016/j.foodchem.2021.130861.