Impact of pitching rate on yeast fermentation performance and beer flavour

The Effect of Sound Frequency and Intensity on Yeast Growth, Fermentation Performance and Volatile Composition of Beer

This study investigated the impact of varying sound conditions (frequency and intensity) on yeast growth, fermentation performance and production of volatile organic compounds (VOCs) in beer. Fermentations were carried out in plastic bags suspended in large water-filled containers fitted with underwater speakers. Ferments were subjected to either 200-800 or 800-2000 Hz at 124 and 140 dB @ 20 µPa. Headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) was used to identify and measure the relative abundance of the VOCs produced. Sound treatment had significant effects on the number of viable yeast cells in suspension at 10 and 24 h (p < 0.05), with control (silence) samples having the highest cell numbers. For wort gravity, there were significant differences between treatments at 24 and 48 h, with the silence control showing the lowest density before all ferments converged to the same final gravity at 140 h. A total of 33 VOCs were identified in the beer samples, including twelve esters, nine alcohols, three acids, three aldehydes, and six hop-derived compounds. Only the abundance of some alcohols showed any consistent response to the sound treatments. These results show that the application of audible sound via underwater transmission to a beer fermentation elicited limited changes to wort gravity and VOCs during fermentation.

FLO11, a Developmental Gene Conferring Impressive Adaptive Plasticity to the Yeast Saccharomyces cerevisiae

The yeast Saccharomyces cerevisiae has a remarkable ability to adapt its lifestyle to fluctuating or hostile environmental conditions. This adaptation most often involves morphological changes such as pseudofilaments, biofilm formation, or cell aggregation in the form of flocs. A prerequisite for these phenotypic changes is the ability to self-adhere and to adhere to abiotic surfaces. This ability is conferred by specialized surface proteins called flocculins, which are encoded by the FLO genes family in this yeast species. This mini-review focuses on the flocculin encoded by FLO11, which differs significantly from other flocculins in domain sequence and mode of genetic and epigenetic regulation, giving it an impressive plasticity that enables yeast cells to swiftly adapt to hostile environments or into new ecological niches. Furthermore, the common features of Flo11p with those of adhesins from pathogenic yeasts make FLO11 a good model to study the molecular mechanism underlying cell adhesion and biofilm formation, which are part of the initial step leading to fungal infections.

Brewer’s Spent Yeast (BSY), an Underutilized Brewing By-Product

The repurposing of by-products and the reduction of waste from food processing streams is an ever-increasing area of interest. Brewer’s spent yeast (BSY) is a prevalent by-product of the brewing industry. The spent yeast cells are removed at the end of the bulk fermentation. A small amount of it is used to start the next batch of fermentation; however, the majority of the spent yeast is discarded. This discarded yeast is high in nutrients, in particular proteins, vitamins and minerals, as well as containing functional and biologically active compounds such as polyphenols, antioxidants, β-glucans and mannoproteins. At present, BSY is mainly used in animal feed as a cheap and readily available source of protein. This review explores alternative, value-added applications for brewer’s spent yeast including nutritional ingredients, functional food additives as well as non-food applications. A major challenge in the utilization of BSY in food for human consumption is the high level of RNA. An excess of RNA in the diet can lead to an increase in uric acid in the bloodstream, potentially causing painful health conditions like gout. This issue can be overcome by RNA degradation and removal via additional treatment, namely heat treatment and enzymatic treatment. There is potential for the use of BSY ingredients in various food applications, including meat substitutes, bakery products and savory snacks.

Chemical Composition of Sour Beer Resulting from Supplementation the Fermentation Medium with Magnesium and Zinc Ions

The bioavailability of minerals, such as zinc and magnesium, has a significant impact on the fermentation process. These metal ions are known to influence the growth and metabolic activity of yeast, but there are few reports on their effects on lactic acid bacteria (LAB) metabolism during sour brewing. This study aimed to evaluate the influence of magnesium and zinc ions on the metabolism of Lactobacillus brevis WLP672 during the fermentation of brewers’ wort. We carried out lactic acid fermentations using wort with different mineral compositions: without supplementation; supplemented with magnesium at 60 mg/L and 120 mg/L; and supplemented with zinc at 0.4 mg/L and 2 mg/L. The concentration of organic acids, pH of the wort and carbohydrate use was determined during fermentation, while aroma compounds, real extract and ethanol were measured after the mixed fermentation. The addition of magnesium ions resulted in the pH of the fermenting wort decreasing more quickly, an increase in the level of L-lactic acid (after 48 h of fermentation) and increased concentrations of some volatile compounds. While zinc supplementation had a negative impact on the L. brevis strain, resulting in a decrease in the L-lactic acid content and a higher pH in the beer. We conclude that zinc supplementation is not recommended in sour beer production using L. brevis WLP672.

Effect of the Ala234Asp replacement in mitochondrial branched-chain amino acid aminotransferase on the production of BCAAs and fusel alcohols in yeast

In the yeast Saccharomyces cerevisiae, the mitochondrial branched-chain amino acid (BCAA) aminotransferase Bat1 plays an important role in the synthesis of BCAAs (valine, leucine, and isoleucine). Our upcoming study (Large et al. bioRχiv. 10.1101/2020.06.26.166157, Large et al. 2020) will show that the heterozygous tetraploid beer yeast strain, Wyeast 1056, which natively has a variant causing one amino acid substitution of Ala234Asp in Bat1 on one of the four chromosomes, produced higher levels of BCAA-derived fusel alcohols in the brewer's wort medium than a derived strain lacking this mutation. Here, we investigated the physiological role of the A234D variant Bat1 in S. cerevisiae. Both bat1∆ and bat1^A234D cells exhibited the same phenotypes relative to the wild-type Bat1 strain-namely, a repressive growth rate in the logarithmic phase; decreases in intracellular valine and leucine content in the logarithmic and stationary growth phases, respectively; an increase in fusel alcohol content in culture medium; and a decrease in the carbon dioxide productivity. These results indicate that amino acid change from Ala to Asp at position 234 led to a functional impairment of Bat1, although homology modeling suggests that Asp234 in the variant Bat1 did not inhibit enzymatic activity directly. KEY POINTS: • Yeast cells expressing Bat1^A234D exhibited a slower growth phenotype. • The Val and Leu levels were decreased in yeast cells expressing Bat1^A234D. • The A234D substitution causes a loss-of-function in Bat1. • The A234D substitution in Bat1 increased fusel alcohol production in yeast cells.

Simultaneous Optimization of Acetaldehyde and DMS Concentrations for Better Sensory Quality of Beer Fermented on an Industrial Scale

The levels of selected volatile components that affected the sensory properties of a lager beer were optimized under high-gravity brewing conditions (15.5 °P) in an industrial plant. The influence of different pitching rates (6–10 million cells/mL), aeration levels (8–12 mg/L), times (4.5–13.5 h) of filling CCTs (cylindroconical tanks, 3850 hl), and fermentation temperatures (8.5–11.5 °C) on the contents of acetaldehyde, diacetyl, acetone, 2,3-pentanedion, dimethyl sulfide (DMS), and on the sensory properties of beer were investigated. Response surface methodology (RSM, Box–Behnken design) was used to research the possibilities for optimizing the concentration of selected volatile components and sensory properties of bottom-fermented lager beers. Statistical analyses of the results showed that the experimental factors had a significant influence (R-squared for the original model with no significant lack-of-fit) on some of the volatile components. Based on the Multiple Response Optimization analysis, the values of independent factors that ensured the highest beer sensory quality were the following: a pitching rate of 10 million cells per mL; a fermentation temperature of 11.5 °C; an aeration level of 12 mg/L; and a CCT filling time of 4.5 h. These results proved that RSM modelling can be successfully applied to optimize fermentation and lagering processes in an industrial plant to manufacture lagers of enhanced sensory quality.

Volatile Esters and Fusel Alcohol Concentrations in Beer Optimized by Modulation of Main Fermentation Parameters in an Industrial Plant

Contents of selected volatile esters and fusel alcohols and their relation to the sensory quality of a bottom-fermented lager beer fermented under high-gravity conditions (15.5 °P) were analyzed using response surface methodology (RSM, Box–Behnken design). The influence of various pitching rates (6–10 mln cells/mL), aeration levels (8–12 mgO2/mL), times (4.5–13.5 h) of filling CCTs (cylindroconical fermentation tanks; 3850 hL), and fermentation temperatures (8.5–11.5 °C) on the contents of selected esters, as well as on concentrations of amyl alcohols and on the sum of higher alcohols in beer, was determined in a commercial brewery fermentation plant. Beers produced throughout the experiments met or exceeded all criteria established for a commercial, marketed beer. Statistical analyses of the results revealed that within the studied ranges of process parameters, models with diversified significance described the concentrations of volatiles in beer. The multiple response optimization procedure analyses showed that the values of process parameters that minimized higher alcohols in beer (97.9 mg/L) and maximized its ethyl acetate (22.0 mg/L) and isoamyl acetate (2.09 mg/L) contents, as well as maximized the sensory quality of beer, (66.4 pts) were the following: Pitching rate 10 mln cells per mL; fermentation temperature 11.5 °C; aeration level 8.8 mg/L; and CCT filling time 4.5 h.

Aromatic Potential of Diverse Non-Conventional Yeast Species for Winemaking and Brewing

Traditionally, Saccharomyces species are those used to conduct industrial alcoholic fermentations. Recently, an increasing interest has arisen with respect to the potential of so-called non-conventional yeasts to improve wine and beer aroma profiles, keeping the particular terroir of each region or for the development of craft beers. In this study, the potential of diverse non-conventional yeasts to improve aroma in winemaking and brewing was investigated, testing several pure and mixed culture combinations. In addition, a comparison between microscale and labscale was carried out in order to assess the value of microwine and microbeer as screening tools. The results indicated that non-Saccharomyces yeasts were good candidates to enhance or diversify aroma profiles in alcoholic beverages, especially regarding acetate ester yield and fruity aromas. However, mixed cultures with Saccharomyces spp. are normally required to achieve a successful fermentation. The adjustment of pithing ratios is crucial for this purpose. Microscale is presented as an effective and efficient screening tool to compare different culture combinations, although scaling-up will always be necessary in order to get results closer to real winemaking or brewing processes.

Adaptive Evolution of Industrial Brewer’s Yeast Strains towards a Snowflake Phenotype

Flocculation or cell aggregation is a well-appreciated characteristic of industrial brewer’s strains, since it allows removal of the cells from the beer in a cost-efficient and environmentally-friendly manner. However, many industrial strains are non-flocculent and genetic interference to increase the flocculation characteristics are not appreciated by the consumers. We applied adaptive laboratory evolution (ALE) to three non-flocculent, industrial Saccharomyces cerevisiae brewer’s strains using small continuous bioreactors (ministats) to obtain an aggregative phenotype, i.e., the “snowflake” phenotype. These aggregates could increase yeast sedimentation considerably. We evaluated the performance of these evolved strains and their produced flavor during lab scale beer fermentations. The small aggregates did not result in a premature sedimentation during the fermentation and did not result in major flavor changes of the produced beer. These results show that ALE could be used to increase the sedimentation behavior of non-flocculent brewer’s strains.

Fermentation of hexoses and pentoses from sugarcane bagasse hydrolysates into ethanol by Spathaspora hagerdaliae

The present study evaluated 13 strains of yeast for ethanol and xylitol production from xylose. Among them, Spathaspora hagerdaliae UFMG-CM-Y303 produced ethanol yields (Y_P/S) of 0.25 g g^- 1 and 0.39 g g^- 1 under aerobic and microaerophilic conditions, respectively, from a mixture of glucose and xylose in flasks. A pH of 5.0 and an inoculum of 3.0 × 10⁸ cells mL^- 1r resulted in the highest ethanol yields. These conditions were tested in a bioreactor for fermenting a medium containing an enzymatic hydrolysate of sugarcane bagasse with 15.5 g L^- 1 of glucose and 3 g L^- 1 of xylose, and achieved a Y_P/S of 0.47 g g^- 1, in relation to total available sugar. These results suggest that S. hagerdaliae UFMG-CM-Y303 has potential for use in second-generation ethanol studies.

Flavor impacts of glycerol in the processing of yeast fermented beverages: a review

Glycerol contributes to the beverage body and fullness. Moreover, it also influences the flavor intensity. As a major byproduct, glycerol not only serves critical roles in yeast osmoregulation and redox balancing, but also acts as the carbon competitor against ethanol in alcoholic fermentation. Therefore, increasing glycerol yield benefits both the flavor and ethanol reduction for the fermented beverages. Glycerol yield has been elevated either by fermentation optimization or by yeast genetic modification. The fermentation optimizations reached maximum 14 g/L glycerol through screening yeast strains and optimizing fermentation parameters. Meanwhile the yeast overexpressing GPD1 (encoding glycerol-3-phosphate dehydrogenase) produced up to 6 folds more glycerol for beer and wine. Except for glycerol improvement, the genetically modified yeasts accumulated dramatically undesirable compounds such as acetaldehyde, acetate and acetoin which are detrimental for beverage flavor. In comparison, the natural high glycerol producers showed strain-specific manner on the yeast-derived aroma compounds like volatile acids, fusel alcohols, esters, and aldehydes. Temperature, sugar concentration, nitrogen composition, oxygen and pH-value, which influence glycerol biosynthesis, also obtained various effects on the production of aromatic compounds. In the current review, we firstly deliberate the organoleptic contributions of glycerol for fermented beverages. Furthermore, glycerol optimization strategies are discussed regarding to the yield improvement, the genes expressions, the overall flavor impacts and the feasibilities in beverage applications. Lastly, for improving beverage flavor by glycerol optimization, a high-throughput platform is proposed to increase the screening capacity of yeast strains and parameters in the processing of fermented beverages.

Yeast: the soul of beer's aroma--a review of flavour-active esters and higher alcohols produced by the brewing yeast

Among the most important factors influencing beer quality is the presence of well-adjusted amounts of higher alcohols and esters. Thus, a heavy body of literature focuses on these substances and on the parameters influencing their production by the brewing yeast. Additionally, the complex metabolic pathways involved in their synthesis require special attention. More than a century of data, mainly in genetic and proteomic fields, has built up enough information to describe in detail each step in the pathway for the synthesis of higher alcohols and their esters, but there is still place for more. Higher alcohols are formed either by anabolism or catabolism (Ehrlich pathway) of amino acids. Esters are formed by enzymatic condensation of organic acids and alcohols. The current paper reviews the up-to-date knowledge in the pathways involving the synthesis of higher alcohols and esters by brewing yeasts. Fermentation parameters affecting yeast response during biosynthesis of these aromatic substances are also fully reviewed.

Effects of Lys and His supplementations on the regulation of nitrogen metabolism in lager yeast

Significant positive correlations between wort fermentability and the assimilation of Lys and His under normal-gravity and high-gravity conditions indicated that Lys and His were the key amino acids for lager yeast during beer brewing. In order to obtain insight into the roles of Lys and His in nitrogen regulation, the influences of Lys, His and their mixture supplementations on the fermentation performance and nitrogen metabolism in lager yeast during high-gravity fermentation were further investigated in the present study. Results showed that Lys and His supplementations improved yeast growth, wort fermentability, ethanol yield and the formation of flavor volatiles. Lys supplementation up-regulated Ssy1p-Ptr3p-Ssy5p (SPS)-regulated genes (LYP1, HIP1, BAP2 and AGP1) dramatically compared to nitrogen catabolite repression (NCR)-sensitive genes (GAP1 and MEP2), whereas His supplementation activated SPS-regulated genes slightly in exponential phase, and repressed NCR-sensitive genes significantly throughout the fermentation. Lys and His supplementations increased the consumption of Glu and Phe, and decreased the consumption of Ser, Trp and Arg. Moreover, Lys and His supplementations exhibited similar effects on the fermentation performance, and were more effective than their mixture supplementation when the same dose was kept. These results demonstrate that both Lys and His are important amino acids for yeast nitrogen metabolism and fermentation performance.

The microbiology of malting and brewing

Brewing beer involves microbial activity at every stage, from raw material production and malting to stability in the package. Most of these activities are desirable, as beer is the result of a traditional food fermentation, but others represent threats to the quality of the final product and must be controlled actively through careful management, the daily task of maltsters and brewers globally. This review collates current knowledge relevant to the biology of brewing yeast, fermentation management, and the microbial ecology of beer and brewing.

Influence of valine and other amino acids on total diacetyl and 2,3-pentanedione levels during fermentation of brewer's wort

Undesirable butter-tasting vicinal diketones are produced as by-products of valine and isoleucine biosynthesis during wort fermentation. One promising method of decreasing diacetyl production is through control of wort valine content since valine is involved in feedback inhibition of enzymes controlling the formation of diacetyl precursors. Here, the influence of valine supplementation, wort amino acid profile and free amino nitrogen content on diacetyl formation during wort fermentation with the lager yeast Saccharomyces pastorianus was investigated. Valine supplementation (100 to 300 mg L⁻¹) resulted in decreased maximum diacetyl concentrations (up to 37 % lower) and diacetyl concentrations at the end of fermentation (up to 33 % lower) in all trials. Composition of the amino acid spectrum of the wort also had an impact on diacetyl and 2,3-pentanedione production during fermentation. No direct correlation between the wort amino acid concentrations and diacetyl production was found, but rather a negative correlation between the uptake rate of valine (and also other branched-chain amino acids) and diacetyl production. Fermentation performance and yeast growth were unaffected by supplementations. Amino acid addition had a minor effect on higher alcohol and ester composition, suggesting that high levels of supplementation could affect the flavour profile of the beer. Modifying amino acid profile of wort, especially with respect to valine and the other branched-chain amino acids, may be an effective way of decreasing the amount of diacetyl formed during fermentation.

Effects of wort gravity and nitrogen level on fermentation performance of brewer's yeast and the formation of flavor volatiles

Normal gravity wort and high gravity wort with different nitrogen levels were used to examine their effects on the fermentation performance of brewer's yeast and the formation of flavor volatiles. Results showed that both the wort gravity and nitrogen level had significant impacts on the growth rate, viability, flocculation, and gene expression of brewer's yeast and the levels of flavor volatiles. The sugar (glucose, maltose, and maltotriose) consumption rates and net cell growth decreased when high gravity worts were used, while these increased with increasing nitrogen level. Moreover, high gravity resulted in lower expression levels of ATF1, BAP2, BAT1, HSP12, and TDH, whereas the higher nitrogen level caused higher expression levels for these genes. Furthermore, the lower nitrogen level resulted in increases in the levels of higher alcohols and esters at high wort gravity. All these results demonstrated that yeast physiology and flavor balance during beer brewing were significantly affected by the wort gravity and nitrogen level.

Inoculation-density-dependent responses and pathway shifts in Saccharomyces cerevisiae

The cell-density-dependent responses of Saccharomyces cerevisiae to inoculation sizes were explored by a proteomic approach. According to their gene ontology, 100 protein spots with differential expression, corresponding to 67 proteins, were identified and classed into 17 different functional groups. Upregulation of eight heat shock, oxidative response and amino acid biosynthesis-related proteins (e.g. Hsp78p, Ssa1p, Hsp60p, Ctt1p, Sod1p, Ahp1p, Met6p and Met17p), which may jointly maintain the cell redox homeostasis, was dependant on inoculation density. Significant increases in the levels of five proteins involved in glycolysis and alcohol biosynthesis pathways (e.g. Glk1p, Fba1p, Eno1p, Pdc1p and Adh1p) might play critical roles in improving ethanol productivity of the fermentation process and shortening the fermentation time when inoculation sizes were increased. Cell-density-dependent glycolytic variations of proteins involved in trehalose, glycerol biosynthesis and pentose phosphate pathway revealed shifts among metabolic pathways during fermentation with different inoculation sizes. Upregulation of three signal transduction proteins (Bmh1p, Bmh2p and Fpr1p) indicated that adequate cell-cell contacts improved cellular communication at high inoculation sizes. These findings provide insights into yeast responses to inoculation size and optimizing the direct inoculation of active dry yeast fermentation, so as to improve the ethanol production.