Simultaneous identification to monitor consortia strain dynamics of four biofuel yeast species during fermentation

Biodiversity and brewing attitude of non-Saccharomyces strains isolated from Uruguayan vineyards and other ecosystems

In recent years, interest in non-Saccharomyces yeasts for the innovation and development of different and alternative beer styles has been increasing, especially for the microbrewing industry. This work studied the biodiversity of non-Saccharomyces yeasts based on isolates from grapes of different Uruguayan vineyards, craft breweries and raw materials, with the aim of selecting autochthonous non-Saccharomyces yeasts with a brewing attitude. Brewing tests were performed on synthetic wort developed for this purpose, and the evolution of alcoholic fermentation was monitored by measuring glucose, maltose, maltotriose consumption, ethanol and glycerol production and final sensory analysis. A total of two hundred seventy-one yeast strains belonging to different genera were evaluated according to these parameters. After evaluating alcoholic fermentation performance, a native yeast strain belonging to the species Starmerella meliponinorum was selected due to its high maltotriose consumption and glycerol production, making it a very promising brewing yeast, especially for production of low carbohydrate beers.

Hanseniaspora vineae and the Concept of Friendly Yeasts to Increase Autochthonous Wine Flavor Diversity

In this perspective, we will explain the concept of “friendly” yeasts for developing wine starters that do not suppress desirable native microbial flora at the initial steps of fermentation, as what usually happens with Saccharomyces strains. Some non-Saccharomyces strains might allow the development of yeast consortia with the native terroir microflora of grapes and its region. The positive contribution of non-Saccharomyces yeasts was underestimated for decades. Avoiding them as spoilage strains and off-flavor producers was the main objective in winemaking. It is understandable, as in our experience after more than 30 years of wine yeast selection, it was shown that no more than 10% of the isolated native strains were positive contributors of superior flavors. Some species that systematically gave desirable flavors during these screening processes were Hanseniaspora vineae and Metschnikowia fructicola. In contrast to the latter, H. vineae is an active fermentative species, and this fact helped to build an improved juice ecosystem, avoiding contaminations of aerobic bacteria and yeasts. Furthermore, this species has a complementary secondary metabolism with S. cerevisiae, increasing flavor complexity with benzenoid and phenylpropanoid synthetic pathways practically inexistent in conventional yeast starters. How does H. vineae share the fermentation niche with other yeast strains? It might be due to the friendly conditions it creates, such as ideal low temperatures and low nitrogen demand during fermentation, reduced synthesis of medium-chain fatty acids, and a rich acetylation capacity of aromatic higher alcohols, well-known inhibitors of many yeasts. We will discuss here how inoculation of H. vineae strains can give the winemaker an opportunity to develop ideal conditions for flavor expression of the microbial terroir without the risk of undesirable strains that can result from spontaneous yeast fermentations.

Biocompatibility in Ternary Fermentations With Lachancea thermotolerans, Other Non-Saccharomyces and Saccharomyces cerevisiae to Control pH and Improve the Sensory Profile of Wines From Warm Areas

Global warming is causing serious problems, especially, in warm regions, where musts with excess sugars and high pH produce wines with decreased freshness and unstable evolution. This study aimed to determine biocompatibility between yeast species, the capacity for microbiological acidification, and the aromatic profile produced in ternary fermentations in which Lachancea thermotolerans has been co-inoculated with Hanseniaspora vineae, Torulaspora delbrueckii, or Metschnikowia pulcherrima, and the fermentation process is subsequently completed with sequential inoculation of Saccharomyces cerevisiae. For this purpose, different cell culture media and instruments were used such as infrared spectroscopy, enzymatic autoanalyzer, chromatograph coupled with a flame ionization detector, spectrophotometric analysis, among others. The behavior of these yeasts was evaluated alone and in co-inoculation, always finishing the fermentation with sequential inoculation of S. cerevisiae, at a stable temperature of 16°C and with a low level of sulfites (25 mg/L) in white must. Significant results were obtained in terms of biocompatibility using population counts (CFU/ml) in differential plating media that permitted monitoring. Quantification of the five species was studied. Concerning acidification by L. thermotolerans in co-inoculations, we showed some metabolic interactions, such as the inhibition of acidification when H. vineae/L. thermotolerans were used, generating just over 0.13 g/L of lactic acid and, conversely, a synergistic effect when M. pulcherrima/L. thermotolerans were used, achieving 3.2 g/L of lactic acid and a reduction in pH of up to 0.33. A diminution in alcohol content higher than 0.6% v/v was observed in co-inoculation with the L. thermotolerans/M. pulcherrima yeasts, with total sugar consumption and very slow completion of fermentation in the inoculations with H. vineae and T. delbrueckii. The aromatic composition of the wines obtained was analyzed and a sensory evaluation conducted, and it was found that both L. thermotolerans and co-inoculations retained more aromatic esters over time and had a lower evolution toward the yellow tones typical of oxidation and that the best sensory evaluation was that of the Lt + Mp co-inoculation. Lachancea thermotolerans and co-inoculations produced wines with low levels of volatile acidity (<0.4 g/L). This work shows that good consortia strategies with binary and ternary fermentations of yeast strains can be a powerful bio-tool for producing more complex wines.