Use of encapsulated yeast for the treatment of stuck and sluggish fermentations

In this work, encapsulated whole cells of S. cerevisiae in calcium-alginate gel ( S. cerevisiae -CAG) were used for the treatment of sluggish and stuck fermentation in vinification. S. cerevisiae -CAG can be applied into the must grape and then they can be withdrawn easily at the end of alcoholic fermentation. For the treatment of sluggish and stuck fermentations, S. cerevisiae -CAG were applied following two steps: firstly S. cerevisiae -CAG were introduced into permeable bags and they were activated in a liquid medium; secondly, after an activation period of eight hours, the immobilized yeast cells were introduced into the fermentation tank. In this work, the obtained results for the treatment of sluggish and stuck fermentations in several French and Portuguese wineries are presented. Preliminary results obtained in micro-vinification conditions have shown that the use of immobilized yeast was better than traditional method (which uses free cells) for the treatment of stuck and sluggish fermentations. The large success rate of immobilized yeast can be explained by one adaptation step of yeast cells to high ethanol concentrations during the immobilization process. The application of immobilized cells of S. cerevisiae under real conditions of vinification has shown a consumption rate of 2.8 g/L per day of reducing sugar with a concentration of 5 million of viable cells per mL. It was never observed any increase of the volatile acidity or of other undesirable compounds.