Abstract
The average ethanol content of wine has increased over the last two decades. This increase was due to consumer preference, and also to climate change that resulted in increased grape maturity at harvest. In the present study, to reduce ethanol content in wine, a microbiological approach was investigated, using immobilized selected strains of non-Saccharomyces yeasts namely Starmerella bombicola, Metschnikowia pulcherrima, Hanseniaspora osmophila, and Hanseniaspora uvarum to start fermentation, followed by inoculation of free Saccharomyces cerevisiae cells. The immobilization procedures, determining high reaction rates, led a feasible sequential inoculation management avoiding possible contamination under actual winemaking. Under these conditions, the immobilized cells metabolized almost 50% of the sugar in 3 days, while S. cerevisiae inoculation completed all of fermentation. The S. bombicola and M. pulcherrima initial fermentations showed the best reductions in the final ethanol content (1.6 and 1.4% v/v, respectively). Resulting wines did not have any negative fermentation products with the exception of H. uvarum sequential fermentation that showed significant amount of ethyl acetate. On the other hand, there were increases in desirable compounds such as glycerol and succinic acid for S. bombicola, geraniol for M. pulcherrima and isoamyl acetate and isoamyl alcohol for H. osmophila sequential fermentations. The overall results indicated that a promising ethanol reduction could be obtained using sequential fermentation of immobilized selected non-Saccharomyces strains. In this way, a suitable timing of second inoculation and an enhancement of analytical profile of wine were obtained.
Highlights
Over the last few decades, there has been a progressive increase in the ethanol content in wine due to new wine styles arising from consumer preference, and to the global climate change that is often associated with increased grape maturity (Jones et al, 2005; Grant, 2010; MacAvoy, 2010; Alstona et al, 2011; Gonzalez et al, 2013)
We evaluated the initial use of immobilized non-Saccharomyces yeast in sequential fermentation trials in terms of reduction of the ethanol content in the wine
The 48 h Synthetic grape juice (SGJ) trials (Figure 1A) showed that the control S. cerevisiae improved the fermentation kinetics compared to the sequential fermentation trials with the initial non-Saccharomyces yeast
Summary
Over the last few decades, there has been a progressive increase in the ethanol content in wine due to new wine styles arising from consumer preference, and to the global climate change that is often associated with increased grape maturity (Jones et al, 2005; Grant, 2010; MacAvoy, 2010; Alstona et al, 2011; Gonzalez et al, 2013). The use of controlled multistarter fermentation using selected cultures of non-Saccharomyces and S. cerevisiae yeast strains has been encouraged (Ciani and Comitini, 2011; Comitini et al, 2011; Domizio et al, 2011; Magyar and Tóth, 2011; Di Maio et al, 2012; Ehsani et al, 2012; Morata et al, 2012; Jolly et al, 2014) In this context, non-Saccharomyces wine yeast and multistarter fermentation might have a role in the reduction of the ethanol content in wine. 1–2% v/v of ethanol reduction was achieved but prolonged time of sequential inoculation or high level of acetic acid were shown (Contreras et al, 2014; Gobbi et al, 2014; Quirós et al, 2014)
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