Ester formation was monitored by solid-phase microextraction (SPME) during alcoholic fermentations of Chardonnay juice. Repeated batch fermentations were conducted with two yeast inoculation levels (0.25 and 0.5g dry yeast/L) and two initial sugar levels (20.6 and 24 Brix). Fermentation profiles, monitored as weight loss throughout fermentation, were similar in all fermentations, although the high Brix fermentations took about 40 hours longer to complete. The percentage of viable cells was also similar during fermentation for all treatments; after fermentation the percentage of viable cells remained high for a longer time when both initial yeast and Brix levels were low. In low sugar (20.6 Brix) juice fermentations, higher yeast inoculation rates resulted in higher concentrations of ethyl acetate, ethyl butyrate, isoamyl acetate, ethyl hexanoate, hexyl acetate, ethyl octanoate, ethyl decanoate compared to fermentations where yeast inoculation rate was lower (t-test, p < 0.001). On the other hand, final concentrations of esters were not significantly different between the different inoculation rates when initial sugar level was high (24 Brix).
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Lee et al. (2004) studied this question.