Screening for new brewing yeasts in the non‐Saccharomyces sector with Torulaspora delbrueckii as model

Abstract

This study describes a screening system for future brewing yeasts focusing on nonSaccharomyces yeasts. The aim was to find new yeast strains that can ferment beer wort into a respectable beer. Ten Torulaspora delbrueckii strains were put through the screening system, which included sugar utilization tests, hop resistance tests, ethanol resistance tests, polymerase chain reaction fingerprinting, propagation tests, amino acid catabolism and anabolism, phenolic off-flavour tests and trial fermentations. Trial fermentations were analysed for extract reduction, pH drop, yeast concentration in bulk fluid and fermentation by-products. All investigated strains were able to partly ferment wort sugars and showed high tolerance to hop compounds and ethanol. One of the investigated yeast strains fermented all the wort sugars and produced a respectable fruity flavour and a beer of average ethanol content with a high volatile flavour compound concentration. Two other strains could possibly be used for pre-fermentation as a bio-flavouring agent for beers that have been postfermented by Saccharomyces strains as a consequence of their low sugar utilization but good flavour-forming properties.

Conventional and Non-Conventional Yeasts in Beer Production

“…Furthermore, the finished beers were characterized by a low real attenuation (37%) and, consequently, low ethanol concentration (2.66% v/v), indicating that T. delbrueckii could be used also to produce low-alcohol beers. Similar results were found by Michel et al [39], which tested 10 T. delbrueckii strains from different habitats and found that two strains can be suitable for producing low-alcohol beer, owing to their inability to ferment maltose and maltotriose, but still produced good flavor. However, these authors found also one strain able to ferment the beer wort to an ethanol concentration of 4% v/v with a desirable fruity and floral aroma, in consequence of production of high amounts of 2-phenylethanol (23.7 mg/L) and amyl alcohols (64.83 mg/L).…”

“…All these results might indicate that the fermentation performance of T. delbrueckii strongly depends on the strain. The overall speed of fermentation seems to be slower than that of usual S. cerevisiae brewing strains; however, this species ferments both high and medium original gravity worts, with a high production of higher alcohols and esters [37,39]. The ethanol content of final beers varied from 0.8 to 4% (v/v), as some strains will not ferment all wort sugars [38,39].…”

“…The overall speed of fermentation seems to be slower than that of usual S. cerevisiae brewing strains; however, this species ferments both high and medium original gravity worts, with a high production of higher alcohols and esters [37,39]. The ethanol content of final beers varied from 0.8 to 4% (v/v), as some strains will not ferment all wort sugars [38,39]. As most studies described an overall fruity flavour in beers obtained by addition of T. delbrueckii, some strains could be suitable for potential use in brewing.…”

Influence of Freeze-Dried Yeast Starter Cultures on Volatile Compounds of Tchapalo, a Traditional Sorghum Beer from Côte d’Ivoire

“…The use of new fermentation technologies for optimizing beer quality and producing beers with particular flavor profiles is one of the worldwide trends in brewing [11,12,14]. In this context, there is a growing demand for new and improved sorghum beer yeast strains to obtain beers with constant organoleptic characteristics.…”

“…In recent years, growth of non-Saccharomyces yeasts has been observed also in fermentation inoculated with S. cerevisiae, suggesting a greater contribution of these yeasts to the flavour and quality of alcoholic beverages than previously thought. Thus, the use of Torulaspora delbrueckii was evaluated for beer production in both pure and mixed cultures with Saccharomyces cerevisiae [11,12]. Other examples of non-Saccharomyces yeasts include Brettanomyces, which is used in atypical spontaneously fermented Belgian beer or "lambic beer" [13] and Candida zemplinina in craft beer fermentation [14].…”