Development of a process for the reduction of grape must malic acid content using immobilized Schizosaccharomyces pombe

Grapes grown in the cooler regions do not always reach proper maturity before they are harvested. This results in grapes with higher acidity than is required to make properly balanced wines. This investigation evaluated the potential use of immobilized Schizosaccharomyces pombe to correct high acidity problems by reducing the malic acid content of musts, without the off-flavors and aromas normally associated with this microorganism. Calcium alginate and kappa-carrageenan were evaluated as the entrapment material for the Schiz. pombe cells. Alginate beads produced significantly higher activity (0.05 probability level) and better mechanical stability. The activity of immobilized Schiz. pombe was enhanced by a 12 hr pre-incubation period in growing media. Malic acid reduction was greater in musts than in wines, for both the batch and the continuous process applications of immobilized Schiz. pombe. After 4 hr, malic acid in must was reduced 84%, whereas reduction was only 50-55% in wines. Using the continuous system, malic acid was reduced 58% in must, but only 10% in wine. Malic acid concentration in musts (red and white) produced from grapes grown at URI was reduced by the use of alginate immobilized Schiz. pombe. One lot was continuously processed through a column packed with the immobilized yeast, another one was deacidified with free yeast in a batch system and the third untreated lot was used as control. The malic acid content of the musts treated by the immobilized system was reduced 40% (white) and 70% (red), and the free cells system deacidified 96% (white) and 90% (red) musts respectively. The three musts were inoculated with Saccharomyces cerevisiae following deacidification and fermentation proceeded for conversion to wine. At the 0.05 probability level sensory evaluation showed a significant preference for the control red wines, in aroma, color, and flavor over the treated wines. For the white wines, there was a significant preference for the control wine over the treated wines in flavor. Nevertheless, the wines deacidified by the immobilized alginate system showed significant preference over the wines fermented with free cells. Even though the treated wines had a lower acceptability, the deacidification through a controlled immobilized system demonstrated significant potential for the wine industry.