OENO One (Apr 2020)
Saccharomyces uvarum yeast isolate consumes acetic acid during fermentation of high sugar juice and juice with high starting volatile acidity
Abstract
Aim: A Saccharomyces uvarum isolate was assessed for its ability to metabolize acetic acid present in juice and during the fermentation of partially dehydrated grapes. The impact on other yeast metabolites was also compared using an S. uvarum isolate and an S. cerevisiae wine yeast. The upper limit of fruit concentration that allowed the S. uvarum isolate to ferment wines to < 5 g/L residual sugar was defined. Methods and results: Cabernet franc grapes were partially dehydrated to three different post-harvest sugar targets (24.5 °Brix, 26.0 °Brix, and 27.5 °Brix) along with non-dehydrated grapes (21.5 °Brix control). Musts from all treatments were vinified with either the S. uvarum isolate CN1, formerly identified as S. bayanus, or S. cerevisiae EC1118. All wines were successfully vinified to less than 5 g/L residual sugar. Fermentation kinetics between the two yeasts were similar for all wines other than 27.5 °Brix, where CN1 took three days longer. During fermentation with CN1, acetic acid peaked on day two, then decreased in concentration, resulting in final wine acetic acid lower than that measured on day two. Wines fermented with EC1118 showed an increase in acetic acid over the time-course of fermentation. Significantly lower wine oxidative compounds (acetic acid, acetaldehyde and ethyl acetate) and higher glycerol resulted in wine produced with CN1 in comparison to EC1118. Both yeasts produced comparable ethanol at each Brix level tested. Further studies showed that CN1 lowered acetic acid seven-fold from 0.48 g/L in juice to 0.07 g/L in wine whereas EC1118 reduced acetic acid to 0.18 g/L. Conclusions: The autochthonous S. uvarum yeast isolate successfully fermented partially dehydrated grapes to < 5 g/L sugar up to 27.5 ºBrix. The consumption rate of acetic acid was faster than its production during fermentation, resulting in low acetic acid, acetaldehyde and ethyl acetate in wine in comparison to a commercial S. cerevisiae yeast while consistently producing higher glycerol. Significance and impact of the study: The S. uvarum yeast isolate can metabolize acetic acid during fermentation to significantly lower acetic acid, ethyl acetate and acetaldehyde in wine. It can also reduce acetic acid by seven-fold from the starting juice to the finished wine, which could have potential application for managing sour rot arising in the vineyard or during the dehydration process in making appassimento-style wines.
