Effects of Cap and Overall Fermentation Temperature on Phenolic Extraction in Cabernet Sauvignon Fermentations

The phenolic content of red wine is responsible for the color, mouthfeel, and aging potential of the wine. Although many fermentation parameters and winemaking techniques affect phenolic extraction, it is generally agreed that one of the prime factors is fermentation temperature; however, temperature is not uniform during fermentation and thermal gradients form between the cap and the liquid. To determine the effects of temperature on phenolic extraction, research scale (120 L) Cabernet Sauvignon fermentations were performed in which the cap and must were either maintained at the same temperature or a constant thermal gradient was maintained between the two during the period of active fermentation. All fermentations were sampled twice daily and phenolic content was determined by reverse-phase high-performance liquid chromatography for the monomeric phenolics and UV-vis spectroscopy for the total anthocyanins and condensed tannins. These experiments showed that cap and must temperature had noticeable effects on phenolic extraction based on where the phenolics originated. For skin phenolics, temperature affected the rate of extraction but not the final concentration, and increasing temperatures favored faster extraction. For seed phenolics, increases in fermentation temperature increased both the rate of extraction and the final concentration. Results showed that must temperature was more important than cap temperature in driving extraction of phenolics.