Selection, Characterization and Oenological Properties of Taiwan Black Queen Grape Wine Yeasts

More than hundreds of private wineries have been established since the Taiwan Tobacco and Alcohol Administration Act was enacted on April 19, 2000. It is essential to screen local wine yeast in order to develop quality wine with unique flavor. 364 yeasts were first isolated from plum, lichee, grape, Black Queen grape, orange, mango, pineapple, carambola and longan must with the supplement of sugar to 17 and 30。Brix, respectively. Among these yeasts, 123 yeasts with CO2 productivity greater than 10 mL after 24 h incubation in YMPG broth containing 10 % glucose were considered as potential yeast isolates. These 123 yeasts were then evaluated for their ethanol productivity in YMPS broth containing 20 % sucrose. Ten yeasts form Black Queen grape and longan with ethanol productivity greater than 5.0 % (v/v) selected for further fermentation properties test. Ethanol contents of fermented YMPS broth were all above 5.0 %(v/v), volatile acidity and turbidity all below 1.2 g/L and 20 NTU, may useable as Black Queen grape and longan wine starter.
Black Queen grape is a main ingredient for red wine brewing in Taiwan. Seven yeasts identified as Saccharomyces cerevisiae by Biolog System with higher ethanol productivity were individually inoculated into Black Queen grape must to undergo fermentation at 25℃ for 14 days. The ethanol contents and volatile acidity in wine were above 15% (v/v) and below 0.7 g/L, respectively. Compared to commercial wine yeasts A, B and C, HP01 fermented red wine contained the highest total ester content, color intensity, taste grade, and overall preference value. On the other hand, HS13 fermented red wine contained the highest ethanol, higher alcohols, fatty acids and phenolic compounds content. The mtDNA restriction fragments profiles of these two wine yeast strains were different from those of other yeast strains. Due to their superiority in oenological characteristics, HP01 and HS13 can be applied in Black Queen red wine brewing to produce red wine with unique flavor.
The effects of several protectants such as rice hull, wheat bran, skim milk, trehalose, and sodium glutamate on the viability of freeze-dried Saccharomyces cerevisiae strains HP01 and HS13 and their fermentation properties such as pH, volatile acidity, ethanol content, titratable acidity, color intensity, phenolic content and residual sugar during grape wine production were investigated. Besides, the effects of storage at 4℃ and 25℃ for 1 to 15 months on the viability and alcoholic fermentation properties of freeze-dried cells and wet cells were also studied. Results showed that the supplement of 10% wheat bran in freeze-drying menstrua could significantly increase the survival rate of freeze-dried HP01 from 25% to 46%. The simultaneous supplement of 10% wheat bran and 20% skim milk increased the survival rate of freeze-dried HP01 to 51%. For the freeze-drying of HS13, the simultaneous supplement of 20% skim milk, 5% honey, and 5% sodium glutamate showed the greatest survival rate, 80% while the survival rate of its control was 9.2%. The fermentation properties of freeze-dried yeasts were like their freshly prepared wet cells; namely, both of them produced 15% ethanol after 9 days fermentation at 25℃. At 4℃ storage, freeze-dried HP01 and HS13 could maintain their viability and fermentation properties as their wet cells for 15 months. While storing at 25℃, the storage lives of freeze-dried cells were less than 2 months.