- Spring 1996 "Update" Newsletter Article -
Yeast study tracks effects in winemaking
From CATI Publication #960401
Copyright © 1996. All rights reserved.
The fine art of winemaking requires the winemaster to maintain a broad knowledge of different yeasts which serve as catalysts for fermentation in the winemaking process.
In a recent experiment on yeast sensitivity at Fresno State's Viticulture and Enology Research Center (VERC), scientists closely monitored the activities of 14 yeasts over two years in an effort to determine which were most sensitive to the detrimental effects of fluoride, a chemical commonly used to control pests on grapevines.
"Fluoride-containing compounds have been shown to be unsurpassed in terms of efficacy and benefit cost ratio for the control of serious vineyard pests such as the grape leaf skeletonizer and omnivorous leaf roller," noted enology professor Carlos Muller, who led the investigation into the reactions of different yeasts with fluoride during the winemaking process.
However, "It has been our experience and there have been several reports from wineries that high levels of fluoride adversely affect fermentation rate," he said. From the vintner's point of view, this sensitivity translates into longer fermentation times and, in some instances, stuck fermentations.
To help determine reactions of yeasts to fluoride-treated grapes from the central San Joaquin Valley, Muller, along with VERC winemaker K.C. Fugelsang and graduate research associate V.L. Wahlstrom, selected 14 commonly available commercial yeasts (Saccharomyces cerevisiae) and subjected them to fluoride- sensitivity testing.
The study "demonstrated the negative impact of fluoride (at both 1 and 3 mg/L) on fermentation rates and final reducing sugar as well as on yeast population," the researchers report.
Over the two years, two of the 14 yeast cultures experienced stuck fermentation and an additional three exhibited signs of protracted fermentation in the presence of fluoride at 3.0 mg/L.
Although the issue is not addressed in this study, results suggest that perhaps other known inhibitors of fermentation may act synergistically with fluoride to exacerbate fermentation problems.
Details of the yeast study are presented in a new research bulletin entitled, "Effect of Fluoride on Fermentation Rate and Population Density in Fourteen Strains of Saccharomyces sp." The bulletin is published by the California Agricultural Technology Institute and is available at no charge. To request a copy, see the Publications Available form on Page 7.{ page top }