Mixed-strain fermentations were carried out with different proportions of killer/sensitive yeasts. It was observed that stuck and sluggish fermentations due to killer/sensitive strain interaction depended on: a. the killer/sensitive yeast proportion at the start of fermentation, b. the concentration of nitrogen source in the grape must, and c. the presence of bentonite during fermentation. The effect of the addition of active carbon and commercial yeast cell walls to sluggish fermentation media was also studied.