Restart of Fermentation of Simulated Stuck Wines by Direct Inoculation of Active Dry Yeasts

Abstract

Fermentation kinetics of nine commercial yeast strains, inoculated at different doses, were studied in a dry wine with fructose added up to 18 or 20 g/L. The ability to complete fermentation appeared to be dose-related for some strains. Other strains appeared to referment to dryness independently of the amount of cells inoculated, while others failed to referment. On average, a dose of 100 g/hL yielded better results than 50 g/hL, but higher doses did not further improve fermentation performance. The effect of pH, SO₂, concentration of alcohol, ammonium ion availability, and temperature on restarting of fermentation was also investigated. The most challenging factors to the yeast were ethanol content and sulfur dioxide levels. In a wine containing a small amount of fructose, the times required for onset and completion of fermentation were inversely related to the amount of alcohol and SO₂. The effect of wine pH was unclear and ammonia addition seemed inefficient, if not inhibitory. The glucose/fructose ratio was found to be crucial for the activity of some strains, while others were less affected by it. Strong differences can be found among yeast strains in their overall sensitivity to wine composition.