Examining the Role of Fructose in Stuck or Sluggish Fermentation: A Correlation, not a Cause
Glycine Z. Jiang,* Christophe P.A. Bonneville,
and Patrick A. Gibney
*Cornell University, Department of Food Science, Stocking Hall,
Ithaca, NY, 14853-7201 (zj43@cornell.edu)
Grape juice is fermented into wine in part by yeast cells (Saccharomyces cerevisiae) converting sugar to carbon dioxide and ethanol. The sugar naturally present in grape juice primarily consists of glucose and fructose in approximately equal quantities. Despite being a carbon source for yeast, fructose has also been implicated as one of the many potential causes of stuck or sluggish fermentations. This is largely based on the observation that stuck fermentations have more residual fructose levels than glucose. However, some evidence indicates that fructose levels simply correlate with stuck fermentations, including growth rates from laboratory strains of yeast, biochemical details of sugar metabolism in yeast, and an increased fructose-to-glucose ratio during fermentations that achieve dryness. This study directly examines the role of fructose in causing stuck or sluggish fermentations through fermentation trials in a variety of matrices (grape juice, synthetic grape juice, laboratory growth medium) while controlling glucose and fructose concentrations. For 70 commercially available wine yeast strains, we observed no consistent growth rate differences between glucose- and fructose-containing growth media. Further, a mathematical model suggests that differences in glucose and fructose anomeric structures underlie differential use of glucose and fructose, rather than regulatory discrimination by yeast cells. Thus, while excess fructose correlates with stuck or sluggish fermentations, it is unlikely to be a cause. This work provides evidence to better understand the role of fructose in fermentations and provide winemakers with more knowledge for making data-based decisions about remediating stuck or sluggish fermentations.
Funding Support: Start-up funding provided to Dr. Patrick A. Gibney by the Department of Food Science, Cornell University.
