3.2. Proteolytic activity of yeasts during alcoholic fermentation optical density changes due to the degradation of azocasein and growth kinetics in the various yeast cultures are shown in Fig. 1A in Fig. 1B, respectively. No variations were observed in non-inoculated must (data not shown) and for T delbrueckii and S. cerevisiae cultures. indicating the absence of protease activity, as already reported in previ- ous study (Charoenchai et al. 1997). In contrast, a marked increase in optical density, indicative of considerable proteolytic activi was ob- served for all Metschnikowia strains tested, with some variation among exhibited the strongest activity, leading to an increase in OD nm up to 0.21. while the M pulcherrima 9 sample only reached 0.17. For all strains except M. pulcherrima Y6259, protease activity was detectable from the beginning of the growth phase, with maximum cumulative activity recorded at the end of growth. For M. pulcherrima Y6259, proteolytic activity was only detected at the end of the growth phase.