Impact of non-Saccharomyces in malolactic fermentation of white and red winemaking

Abstract

Nowadays the use of non-Saccharomyces as starters of alcoholic fermentation (AF) has increased because of the modulation of the organoleptic profile of wines. Additionally, these wines can undergo a malolactic fermentation (MLF) driven out by lactic acid bacteria, mainly Oenococcus oeni. Since MLF is usually performed after AF, MLF is highly influenced by the metabolism of the yeasts that have conducted the AF. 

In the present work, we tested the oenological impact of sequential AF with Torulaspora delbrueckii or Metschnikowia pulcherrima with Saccharomyces cerevisiae on the MLF. Grape musts of Macabeu and Cabernet Sauvignon from 2018 vintage were inoculated with the two non-Saccharomyces. After 48h, the fermenting musts were inoculated with S. cerevisiae. Musts inoculated with only S. cerevisiae were used as control. After AF, wines were racked and stabilized at 7 ºC for a week. Two O. oeni strains were used to perform MLF of wines corrected in L-malic acid concentration and pH. Also, a spontaneous MLF was followed. General oenological parameters, volatile and phenolic compounds, organic acids and AF and MLF kinetics were studied. 

Generally, wines were chemically similar, being the ones fermented with T. delbrueckii more different. In all AF the non-Saccharomyces imposition was >90% at 48 h but at the end of AF stage S. cerevisiae is the sole dominant species. Moreover, the MLF finished earlier when a non-Saccharomyces was previously been inoculated. In this way, MLF of red wines was already completed spontaneously when AF finished. All MLF finished in less than 8 days with the exception of the spontaneous one in S. cerevisiae wine (17 days). Overall, the inoculated MLF were quicker than the spontaneous MLF, apart from an inoculated O. oeni strain in M. pulcherrima wine. Citric acid was completely consumed after MLF except in the spontaneous MLF of S. cerevisiae wine. According to the volatile analyses, the fermentation with T. delbrueckii lead a reduction of medium-chain fatty acid concentration. The sensorial analyses showed that the lactic character was highly noticed by the testers in the spontaneous MLF, highlighting the one of M. pulcherrima sequential AF. 

To sum up, MLF was highly influenced by both the AF strategy (presence of non-Saccharomyces) and the strain of O. oeni. Wines obtained with T. delbrueckii seem to be more MLF friendly, allowing quick MLF and developing wines more different from S. cerevisiae, being the best rated by the testers.