Studies on Controlled Fermentations III

¹ Department of Viticulture and Enology University of California, Davis

1. At 60°F, oxygen or carbon dioxide at 1.0 lpm had no influence on the rate of fermentation of musts from immature grapes. For California musts at this or higher temperatures, it is difficult to speed up or slow down the rate of fermentation by use of oxygen, nitrogen, air, or carbon dioxide. This is in contrast to the general retarding influence of anaerobic fermentations noted with Bordeaux musts.

2. At 55°F, carbon dioxide at 1.0 lpm retards the rate of fermentation but has little influence on quality. The optimum fermentation temperature for white table wine appears to be about 50°-55°F.

3. Fermentations under pressure produce slightly more volatile acidity. Temperature control seems to be a simpler and better means of controlling the rate and extent of fermentation with California musts. This is supported by some German and by Austrian and South African results. With sugared German musts favorable results have been obtained with pressure fermentations, but few comparable checks fermented at controlled low temperatures seemed to have been made.

4. Fermentation temperatures of 70° and 80°F, with cap temperatures held to 90°F or less, seem to be the best to use with low-color grapes such as Pinot noir. Fermentation temperatures of 50°F or 60°F give poorer flavors and reduced color extraction, and should not be employed in the fermentation of red musts.

5. The pre-heating of red grape musts to 140°F or 160°F causes more complete color extraction than submerged-cap fermentation, but more tannin is extracted from the dead cells after fermentation starts. Berg and Marsh (5) have shown that heat extraction without fermentation on the skins has both advantages and disadvantages; increased color, higher costs, higher pectin extraction, higher tannin extraction, etc.

6. High color and tannin extraction from red musts can be effected by stirring. There is slightly more aldehyde and tannin accumulation with this method. Problems also arise with clarification of the wines.

7. Submerged-cap fermentations give less color extraction than the other methods at comparable temperatures, probably because of the lower cap-liquid temperature differential.

8. The most efficient and practical method for color extraction in a winery is either pumping over or punching down when a reasonable amount of color can be obtained from the must.