Grape must was fermented by a mixed culture of Saccharomyces cerevisiae W-3 (a wine yeast) and Issatchenkia orientalis KMBL 5774 (a malic acid-degrading yeast). Co-fermentation with 1:1 (v/v) inoculum ratio of W-3 and KMBL 5774 decreased malic acid to 0.33 mg/ml from 1.1 mg ml with W-3 alone. Ethanol production was the same in both cases (7.8%, v/v). Acetaldehyde, 1-propanol, 2-butanol and isoamyl alcohol all decreased, with an increase in methanol, in the co-fermented wine. Sensory evaluation showed a higher score in the wine fermented with 1:1 (v/v) inoculum ratio than those obtained by 4:1 (v/v) inoculum ratio or W-3 alone.

No abstract

Aims:  To test degradation of malic acid content in wine by immobilized Issatchenkia orientalis KMBL 5774 cells recently isolated from Korean wine pomace as a malic acid‐degrading yeast. Methods and Results:  I. orientalis KMBL 5774 cells were immobilized using a mixture of oriental oak (Quercus variabilis) charcoal with sodium alginate. When the immobilized yeast cells were observed on a scanning electron microscope, cells were efficiently immobilized on the surface area of the charcoal. A Korean wine containing a high level of malic acid was treated with the immobilized yeast cells. The HPLC analysis of the malic acid content in the treated wine showed the malic acid content was reduced to 0·75 mg ml−1 after treatment from the original content of 8·96 mg ml−1, representing 91·6% of the malic acid was degraded during the treatment. Conclusions:  The immobilization of the malic acid‐degrading yeasts with oriental oak charcoal and sodium alginate is useful for degradation of malic acid in wines containing a high level of malic acid with no significant increase in other acids. Significance and Impact of the study:  Malic acid is sometimes detrimental to the quality of wines when present at high concentrations in some varieties. The immobilized I. orientalis KMBL5774 cells appear to be a promising candidate in view of developing biotechnological methods for reduction of malic acid contents in wine.

Several indigenous sulfite-resistant yeasts were isolated at the microbial succession stage of yeast flora during spontaneous fermentation of Campbell Early grapes using a YPD plate that contained 200 mg/L or 500 mg/L potassium metabisulfite. When they were applied to the wine fermentation using the Campbell Early grape and apple juices, strains S13 and D8 showed strong alcohol fermentation and good flavor production. They were identified as Saccharomyces cerevisiae in the phylogenetic analysis based on their ITS 1-5.8S-ITS II DNA sequences. The two yeast strains grew to a high cell density in the YPD media supplemented with 40%(w/v) glucose. They also grew rapidly in the YPD media at 40°C. While strain S13 showed some differences in cell density at the two temperatures, no marked difference was observed during the culture of strain D8. The strains grew relatively well at pH 5.0 and 9.0 compared with pH 7.0, which was the optimum pH for their growth. Especially, strain S13 cultivated in the YPD media at pH 9.0 grew to 93% of the growth of strain D8, which was obtained at pH 7.0.

Cryoextraction (a freeze concentration using an instrument) can increase the sugar concentration in grape juice by reducing its water content, similar to the natural freezing of grapes for natural ice wine. In this study, fermentation of freeze-concentrated Campbell Early grape (Vitis labruscana) juice to 36 °Bx was carried out using Saccharomyces cerevisiae strains D8 and S13 isolated from Korean grapes. During the fermentation, strains S13 and D8 showed rapid sugar reduction and alcohol production compared with S. cerevisiae Fermivin ® used as a control. After nine-day fermentation, the residual sugar contents were lower in W13(9.77%) and D8 wine(9.07) than that in Fermivin ® wine(14.0%). Total acid content was high in the D8>S13>Fermivin ® wine, in that order. The acetaldehyde content was highest in the D8 wine and lowest in the Fermivin ® wine, among the three. The methanol content was slightly higher in the S13 and D8 wines than in the Fermivin ® wine. In the sensory evaluation, the S13 wine exhibited the highest score in flavor and taste among the three wines. Both the two S13 and D8 wines exhibited higher scores than Fermivin ® wine in overall preference.