Screening Of Sparkling Wine's Yeast Strains

The quality and character of wine are mainly determined by four factors: ecological condition and grape varieties, technology, brewing equipment and fermentation microbiology. The zymurgy's character of microbiology is the dicisive factor under the hypothesis that the others are relative steady. Wine yeasts are important microorganisms in winemaking. Their diversities and identification are the main bases to screen excellent stains. Strains isolated from wine producing regions are usually more adapted to their own climatic conditions, grapes and also partially responsible for wine quality and style. At present, more and more special or exclusive yeasts has been used in the market, which just were applicable to special wines and particular regions and replaced regularly eurytropy yeasts. We can not deny that wine yeasts are very important for wine quality and style.Shacheng is one of famous and long history wine producing region in China. Many wineries located in here. Yeast strains were isolated and screened in Great Wall Wine Co., LTD and Sino-France chateau. Yeast strains were isolated from winery environment, earth of vineyard, grapes, and SO2 and alcohol treatments and untreatment spontaneousness fermentation. The influence of SO2 and alcohol treatments on yeast floras was also researched. Strains were preliminarily classified on WL medium. Then typical and pure cultured yeasts were chose and identificated by PCR/RFLP of 5.8S-ITS method. All the Strains belonging to Saccharomyces cerevisiae were used to screen excellent sparkling wine yeasts.Isolation and IdentificationThe 562 yeasts isolated in our experiment were belonging to 15 classified types after 5 days on WL medium according to the colony colour and morphology. Then some strains were chose in accordance to the strain numbers of every types and identified by PCR/RFLP analysis of the amplification fragments of 5.8S-ITS.The proportion of strains identified as S. cerevisiae was 51.7%, 291strains in all yeast strains, mostly came from spontaneous fermentation. There were 44 strains belonging to Kloeckera apiculata, 7.8% proportion. The least was Brettanomyces bruxellensis, 6 strains, just 1.1%.The Influence on Yeast Floras from Spontaneous Fermentation under Different SO2 and Alcohol Treatment MethodsIn the spontaneous fermentation experimentation under SO2 and alcohol treatments, the yeast floras firstly starting fermentation were insensitive to SO2 and lower tolerance to alcohol, subsequently, such as Pichia and Cryptococcus, were sensitive to SO2. The rise and decline of yeast floras during prime fermentation phase was influenced by not only SO2 but also alcohol concentration. From middle to final stage, S. cerevisiae were almost majority, but still some strains which tolerance to SO2 and alcohol were higher were isolated also, for instance Saccharomyces bayanus and Zygosaccharomyces bailii.Screening of Excellent Sparkling Wine Yeast StrainsThere were 291 strains identified as S. cerevisiae, which been used to screening experiment through various tests. After prescreening on producing gas capability, 62 wine yeast strains has been selected which bubble was fine and permanence. Z27,Z25,Z28 were the final excellent three yeast trains after autolysis, flocculability, producing gas capability and tolerance of alcohol, SO2 and low temperature fermentation capability tests.Tasting and Analysis of Sparkling WineTotal 48 kinds aroma compounds were detected by GC/MS analysis from sparkling wines and base wine, of which 45 kinds in base, 46 kinds in sparkling wines fermented by strains Z25, Z28 and CK. The content of alcohol, acid and ester total up to 82.8% in all aroma composition, alcohol was the leading composition, next were acid and ester. The content of aroma compounds in all five wine samples increased compare with that of existing in base wine after second fermentation, but the quantity depends on strains.