Biomass from agricultural waste can be an excellent source of sustainable energy, the most notable of which is bioethanol. This study aimed to adapt and improve bioethanol production using a yeast strain that ferments the sugar content in undiluted and non-added nutrient vineplant bunch hydrolysates. Yeasts that were previously isolated and molecularly characterized were screened for their pentose fermenting capabilities, first in solid and then liquid mediums. Then, 10 native xylose fermenting yeast strains were tested for their ability to produce ethanol from acid hydrolysates from vineplant lignocellulosic waste. The five strains that exhibited the highest ethanol production underwent fermentation in the pure (non-detoxified) hydrolysate. The strain Pichia kudriavzevii D12 in the undiluted hydrolysate medium gave the highest ethanol concentrations and yields. Hence, P. kudriavzevii was selected for adaptation with sequential fermentations. As a result, a 59% increase in the ethanol production (g/L) was recorded for the D12 strain in the undiluted hydrolysate medium during the adaptation studies. A 2.9-fold increase in the yield (g/g) was obtained for this sample when compared with the reference medium. This study determined that a nondetoxified, organic waste medium prepared from vineplant bunches without added nutrients is a suitable substrate alternative for bioethanol production.