In alcohol distilleries the ethanol content in recycled yeast suspension range from 2% to 3%. Recycling yeast cells is a useful tool to inoculate another fermentation batch or to continuous fermentation. The ethanolic fermentation and yeast recovering were evaluated in laboratory. The yeast suspension recovered from the wine, by centrifugation, was treated before re-inoculation in new fermentation media, to evaluate the ethanol and other metabolites toxic effect influences in the next fermentations batch. The Saccharomyces cerevisiae IZ-1904 strain was used to inoculate molasses medium with 180g L-1 and 310g L-1 of total reducing sugars (TRS). The yeasts recovering treatment was made with double centrifugation and yeast suspension in water and wine. Eight sequential batch fermentations were done, each with three replications. The first fermentation with fresh yeast, and others with recycled cells. The high sugar content was necessary to generate elevated ethanol concentration in the wine, and to confer hard fermentation conditions so the effects of any toxic compounds were introduced and more easily detected. In fermentations with less than 6.4% ethanol (v v-1) there was no toxic effect detected. The ethanol and other metabolites inhibition on yeast were detected and the results showed that the reduction of those components from the recycled yeast suspension might optimize the fermentation process. Ethanol production and yeast death rate were affected by the recycling of ethanol.
alcoholic fermentation; recycle; metabolites; inhibition
