Abstract
In wine fermentation process, yeast species are essential for providing good taste of wine. Effective yeast also can be grown under limited essential nutrients especially nitrogen. However, limitation of nitrogen source leads to stress condition which induce yeast to produce hydrogen sulfide (H2 S) resulting in unacceptable quality of wine. Moreover, it may lead to incomplete fermentation process. This research focused on isolation of natural yeasts in five grape varieties (Syrah Granmonte, Syrah J&J, Durif, Viognier and Chenin blanc) growing in Thai vineyard and evaluation their ability to grow in low nitrogen condition during fermentation without H2S production and providing a good flavor of wine. The relationship between isolated yeasts on yeast assimilable nitrogen (YAN), viable cell count, soluble solid and sensory test were determined during four week of fermentation. The results showed that isolated yeast from Viognier grape variety was the best performance for longest fermentation without H2S production. The highest viable cell in certain isolate was found at 1.02 x 108 CFU/ml with highest YAN as 262.5 mgN/L. In addition, sensory evaluation by cultivation of grapes and wine director, viticulture and winemaking from Asoke valley winery, found that isolated yeast from Viognier grape provided the best flavor with rich alcohol taste from the second week of fermentation while the sugar taste was relatively low. Furthermore, nucleotide sequencing data at 26S RNA gene showed that potential isolated yeasts all belong to Saccharomyces cerevisiae NRRL Y-12632 (100% similarity) which is GRAS (General Regard as Safe) species. Therefore, this suggests that three isolated yeasts (Granmonte, Viognier and J&J Syrah varieties) have potential for further development in wine fermentation process with minimal nitrogen requirement.
