Effects of Some Treatments of Grape Juice on the Population and Growth of Yeast Species During Fermentation

¹ Faculty of Sciences, University of Illes Balears, E07071 Palma de Mallorca, Spain.

The effects of grape juice clarification on the initial population and growth of wild yeasts were studied. Two musts were clarified using different treatments. One of them was treated with pectolytic enzyme, and then a single cold treatment at 3°C to 5°C was performed. The other must was submitted to an additional cold settling treatment combined with bentonite, gelatine, and coloidal silica. Despite the different occurrences of yeast species in the musts, the effects of the treatments were similar. The population of almost all yeasts decreased during the clarification, yet at the end of the treatment the levels reached were similar to those existing at the beginning of the process. The extent of removal of yeasts depended on each particular species. The most affected yeasts were Issatchenkia terricola, Hansenula anomala, and Saccharomyces cerevisiae. An unexpected proliferation of Pichia membranaefaciens in the early stages of the fermentation was observed. This fact was a consequence of the changes in the relative populations of the yeast species during clarification of the must.

Key words: yeast, clarification, grape must, Pichia membranaefaciens

Submitted on June 6, 1990