Dynamic Changes in Ester Formation during Chardonnay Juice Fermentations with Different Yeast Inoculation and Initial Brix Conditions

¹ Korea Food Research Institute, Sungnam-si, Kyeonggi-do, 463-420 Korea
² Yering Station, Yering, 3770 Australia
³ E&J Gallo Winery, Modesto, CA 95353
⁴ Technische Universität Braunschweig, D-38106 Braunschweig, Germany
⁵ Department of Viticulture and Enology, University of California, Davis, CA 95616.

email: seebeler{at}ucdavis.edu

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).

Note:
Acknowledgments: This work was supported by a grant from the American Vineyard Foundation and the California Competitive Grant Program for Research in Viticulture and Enology. The authors thank Linda Bisson for helpful discussions and review of this manuscript.

Key words: esters, grape juice, yeast, inoculation, fermentation, sugar content, solid-phase microextraction, gas chromatography