The Nature and Cause of Cap-Liquid Temperature Differences During Wine Fermentation

Abstract

During pilot-scale fermentations of grape musts in 200 and 250-gal tanks the temperatures of bulk liquid and of cap were measured by thermocouples and a recording potentiometer. Periodic samples of the bulk liquid and of liquid expressed from the cap were analyzed for alcohol and reducing sugar. The results show that the large temperature rise in the floating cap during fermentation on the skins is caused by a faster fermentation of the sugar in the liquid adhering to the cap than in the bulk liquid. Temperature differentials between cap and liquid were maximum, about 15 to 20°F (8 to 11°C), during the early stages of vigorous fermentation. Vertical and lateral temperature gradients were significant in both cap and liquid, though greater in the cap. On the other hand, the temperatures during the fermentation of free-run juice were essentially uniform throughout the tank liquid.