Diagnosis and Rectification of Stuck and Sluggish Fermentations

Abstract

Suboptimal fermentation rates and incomplete sugar utilization are symptoms of environmental or physiological stress imposed upon the yeast Saccharomyces. The ability to restart an arrested fermentation and to increase the rate of one that is sluggish depends upon correctly diagnosing the root cause of the problem for the yeast. Careful analysis of fermentation conditions and of the fermentation profile can provide clues to the reason for poor fermentation performance. Astute monitoring of the fermentation can assist the winemaker in early identification of problem fermentations. Proper analysis of juice composition and careful attention to yeast nutritional and physiological needs can reduce the incidence of arrest of fermentation. Problem fermentations can be divided into four general categories: sluggish initiation, rate eventually becoming normal; sluggish initiation slow rate throughout the fermentation; normal initiation of fermentation, becoming sluggish; and a normal fermentation that abruptly arrests. Each type of problem fermentation is associated with different types of stress for the yeast.