| Popis: |
For many years it has been standard practice in wine-making to use pure cultures of oenologically suitable species, in particular Saccharomyces cerevisiae and its physiological variants. Positive properties of some non-Saccharomyces yeasts could be also used in wine production. Although the use of must as fermentation medium is a common practice to study and compare different yeast strains, its use is limited because it is not available throughout the whole year, and variations in composition can be significant regarding geographycal and climate differencies. In this work a new standard and easy available medium was selected. The fermentation of standard medium was done at 12 ^oC using different yeasts: CS-2 (identified as Saccharomyces cerevisiae, previously isolated from Cabernet Sauvignon grapes) CH-3 (isolated from Chardonnay grapes and identified as Torulaspora delbrueckii, which was classified before as Saccharomyces rosei), Saccharomyces bayanus strain Z-2 (Collection of microorganisms of Faculty of Food Technology and Biotechnology, Zagreb, Croatia) and two comercial strains of wine yeast, UVAFERM and UVAFERM 228. Fermentation profiles were monitored by measuring CO_2 evolution and CO_2 production rate. At the end of fermentation, concentrations of reducing sugars, alcohols, total and volatile acidity were determined in centrifuged samples. The maximum fermentation rate was obtained between the sixth and eighth day with all yeast strains. UVAFERM strain finished the fermentation first, followed by Z-2, CS-2 and UVAFERM 228, and CH-3 was the slowest. All fermentations were carried on to the completion. The highest ethanol concentration was produced by Z-2 (9,88 %vol.) and the lowest by CH-3 (9,25 % vol.). The greatest change of total acidity was obtained by strain CH-3. H_2S assessment on BiGGY agar showed that strain CS-2 produced the lowest and UVAFERM 228 the biggest amount of H_2S. |
