Yeast adaptation for very high gravity fermentation In ethanol production process, the distillation of sugarcane fermented must result in large volume of vinasse. For each liter of ethanol produced around 12 liters of vinasse are generated. Due to the vinasse application limit per area, established by CETESB, the costs to manage this waste became very high (R$ 17,33 per m 3 , considering the distribution by truck for a distance of 20 to 25 km). This led the sugarcane industry to seek alternatives to reduce the volume of vinasse produced. The process of fermentation with high alcohol content is one of the options; it can reduce by 50% the volume of vinasse generated and presents numerous technical, economic and environmental advantages. For these reasons, the aim of this study was to adapt the yeasts strains C22 and Y904 for fermentations with high alcohol levels and verify the morphological changes of C22 and Y904 strains in the process of adaptation and fermentation with high alcohol content, by scanning electron microscopy (SEM). For this purpose, fermentations with increasing concentrations of sugar in the must (50 to 274.52 g L-1) were performing. In the fermentation cycle with high alcohol content, the viability of C22 and Y904 yeast adapted was 70.1% (83.5% and 56.7%, respectively); the viability of the yeast C22 and Y904 unadapted was 62% (68.8% and 55.2%, respectively). The SEM images showed that the C22 adapted strain presented better morphological response to stress exposure than other yeast strains. We conclude that the choice of yeast strain and his previous adaptation are essential for conducting fermentations with high alcohol content.