Three hundred and seventeen strains representing 20 species of yeasts were screened for the presence of beta-glucosidase activity. All of the strains of the species Debaryomyces castellii, Deb. hansenii, Deb. polymorphus, Kloeckera apiculata and Hansenula anomala showed beta-glucosidase activity, but only one of 153 strains of Saccharomyces cerevisiae. The other species behaved differently, depending upon the strain. The strains that hydrolysed arbutin were checked to localize the beta-glucosidase activity. A strain of Deb. hansenii exhibited the highest exocellular activity and some wall-bound and intracellular activity. The beta-glucosidase synthesis from this yeast was enhanced by aerobic conditions of growth, was repressed by high glucose concentration (9%) and occurred during exponential growth. The optimum conditions for enzymatic preparations of Deb. hansenii were between pH 4.0 and 5.0 and 40 degrees C. A high concentration of ethanol and glucose did not reduce the enzymatic activity. The enzymatic preparations of Deb. hansenii released monoterpenols and other alcohols from a grape glycoside extract.

During the course of this study, a new, rapid and reproducible method to assay beta-glucosidase activity was developed. The fact that Saccharomyces and non-Saccharomyces yeast strains are able to express beta-glucosidase activity during the alcoholic fermentation sheds new light on the contribution of these yeasts in the aroma expression of wines.

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The present study was undertaken to evaluate the influence of medium pH and inoculation time on the growth and malolactic activity of an Oenococcus oeni culture. Samples of a commercial white grape juice adjusted to pH 3.2, 3.4 or 3.6, and inoculated with Saccharomyces cerevisiae strain CY3079, were inoculated with a malolactic culture (Oenococcus oeni strain 31) at the beginning, middle, and end of alcoholic fermentation. The results obtained from this single case study show that it is possible to inoculate the bacterial culture at the three different times during alcoholic fermentation without slowing down or stopping alcoholic fermentation or causing failure of MLF. However, pH and timing of bacterial inoculation were critical to how rapidly MLF starts. At pH 3.2 a lowering of bacterial viability was observed, but a more important reduction was recorded at all tested pH levels when the bacteria were inoculated halfway through alcoholic fermentation. When inoculation was carried out at the end of alcoholic fermentation, the presence of yeast seemed to favour bacterial viability and activity and bacteria performed MLF even in difficult conditions such as pH values around 3. In all wines malolactic fermentation was accompanied by total degradation of malic and citric acids and production of L-lactic acid, D-lactic and acetic acids. AbbreviationsAF alcoholic fermentation; MLF malolactic fermentation; MRS de Man, Rogosa and Sharpe; YM yeast and mould

Different types of oenotannins were added to Vitis vinifera cv. Sangiovese grapes of various composition and the resulting wine color parameters were measured, including intensity, hue, total phenol index, monomer anthocyanin content, and colored polymeric pigment content. Oenotannins were also tested during pre-and postfermentation on grapes harvested in 2003 from two growing areas. Grapes from the 2004 harvest were tested at different ripeness using only oenotannins exhibiting the best wine color stabilization in 2003. The response of different oenotannins varied according to grape characteristics, with gallnut and grape seed tannins most reliably stabilizing and increasing color intensity even after six months of storage. The same tannins positively affected wine color stabilization, an effect further enhanced in wine produced from less ripe grapes. Timing of oenotannin addition and grape characteristics had a significant effect on color intensity and stabilization. The estimation of grape phenolic maturity may allow for improved wine color characteristics by tailoring the use of oenotannins.