The molecular biology of fruity and floral aromas in beer and other alcoholic beverages

Advancements and challenges for brewing aroma-enhancement fruit wines: Microbial metabolizing and brewing techniques

Aroma, a principal determinant of consumer preference for fruit wines, has recently garnered much attention. Fruit wines brewing was concomitant with complex biochemical reactions, in which a variety of compounds jointly contribute to the aroma quality. To date, the mechanisms underlying the synthesis of aroma compounds and biological regulation methods in fruit wines have remained ambiguous, hindering the further improvement of fruit wines sensory profiles. This review provides a detailed account of the synthesis and regulatory mechanisms of typical aroma compounds and their contributions to the characteristics of wines. Additionally, Comprehensive involves between microflora and the formation of aroma compounds have been emphasized. The microflora-mediated aroma compounds evolution can be controlled by key fermentation techniques to protect and enhance. Meanwhile, the genes impacting key aroma compounds can be identified, which provide references for the rapid screening of aroma-enhanced strains as well as target formation of aroma by modifying relative genes.

Characterization of key aroma-active compounds in fermented chili pepper (Capsicum frutescens L.) using instrumental and sensory techniques

The aroma profile of fermented chili pepper was analyzed using gas chromatography-mass spectrometry (GC-MS) coupled with chromatography-olfactometry (GC-O). A total of 19 aroma-active compounds were detected, exhibiting aroma intensities spanning from 1.8 to 4.2. And 12 aroma-active compounds were determined as pivotal odorants through odor activity value (OAV) calculation. Concentrations of these aroma-active compounds were quantified and subsequently employed in reconstructing the aroma profile of fermented chili pepper. Quantitative descriptive sensory analysis and electronic nose analysis proved that the aroma profile of fermented chili pepper was basically reconstituted. Omission experiments confirmed that methyl salicylate, linalool, 2-methoxy-3-isobutylpyrazine, and phenylethyl alcohol were the key aroma-active compounds of fermented chili pepper. Moreover, the perceptual interactions between the key aroma-active compounds were investigated. It was found that methyl salicylate masked the floral aroma, while phenylethyl alcohol had an additive effect on the aroma of linalool and 2-methoxy-3-isobutylpyrazine.

Impact of non-Saccharomyces yeasts derived from traditional fermented foods on beer aroma: Analysis based on HS-SPME-GC/MS combined with chemometrics

In recent years, numerous studies have demonstrated the significant potential of non-Saccharomyces yeasts in aroma generation during fermentation. In this study, 134 strains of yeast were isolated from traditional fermented foods. Subsequently, through primary and tertiary screening, 28 strains of aroma-producing non-Saccharomyces yeast were selected for beer brewing. Headspace-solid phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS) and chemometrics were employed to analyze the volatile flavor substances in beer samples fermented using these strains. Chemometric analysis revealed that distinct species of non-Saccharomyces yeast had a unique influence on beer aroma, with strains from the same genus producing more similar flavor profiles. Accordingly, 2,6-nonadienal, 1-pentanol, phenyl ethanol, isoamyl acetate, ethyl caprate, butyl butyrate, ethyl propionate, furfuryl alcohol, phenethyl acetate, ethyl butyrate, ethyl laurate, acetic acid, and 3-methyl-4 heptanone were identified as the key aroma compounds for distinguishing among different non-Saccharomyces yeast species. This work provides useful insights into the aroma-producing characteristics of different non-Saccharomyces yeasts to reference the targeted improvement of beer aroma.

Effect of cooking methods on volatile compounds and texture properties in maize porridge

To investigate the optimal processing of maize porridge, the volatile compounds and texture under different cooking methods and time have been studied. A total of 51 volatile compounds were identified in maize porridge. Notably, the major volatiles, aldehydes and esters exhibited a relatively high content in electric pressure cooker (EPC), and esters tend to significantly increase after cooking. Among aldehydes, nonanal and hexanal played a great role in flavor due to their relatively high content. Volatile compounds of maize porridge in different cooking methods could be clearly distinguished by multiple chemometrics. Furthermore, texture analysis revealed that almost all the indicators in the EPC can reach the lowest value at 60 min. To summarize, different cooking methods had a more significant influence on the volatile compounds and texture compared to time. This study helps to improve the sensory attributes of maize porridge, and thus contributes to healthier and more sustainable production.

First Report on Mycotoxin Contamination of Hops (Humulus lupulus L.)

The presence of mycotoxins and other toxic metabolites in hops (Humulus lupulus L.) was assessed for the first time. In total, 62 hop samples were sampled in craft breweries, and analyzed by a multi-toxin LS-MS/MS method. The study collected samples from craft breweries in all of the Croatian counties and statistically compared the results. Based on previous reports on Alternaria spp. and Fusarium spp. contamination of hops, the study confirmed the contamination of hops with these toxins. Alternaria toxins, particularly tenuazonic acid, were found in all tested samples, while Fusarium toxins, including deoxynivalenol, were present in 98% of samples. However, no Aspergillus or Penicillium metabolites were detected, indicating proper storage conditions. In addition to the Alternaria and Fusarium toxins, abscisic acid, a drought stress indicator in hops, was also detected, as well as several unspecific metabolites. The findings suggest the need for monitoring, risk assessment, and potential regulation of Alternaria and Fusarium toxins in hops to ensure the safety of hop usage in the brewing and pharmaceutical industries. Also, four local wild varieties were tested, with similar results to the commercial varieties for toxin contamination, but the statistically significant regional differences in toxin occurrence highlight the importance and need for targeted monitoring.

Microbial β C-S Lyases: Enzymes with Multifaceted Roles in Flavor Generation

β C-S lyases (β-CSLs; EC 4.4.1.8) are enzymes catalyzing the dissociation of β carbon-sulfur bonds of cysteine S-conjugates to produce odorant metabolites with a free thiol group. These enzymes are increasingly studied for their role in flavor generation in a variety of food products, whether these processes occur directly in plants, by microbial β-CSLs during fermentation, or in the mouth under the action of the oral microbiota. Microbial β-CSLs react with sulfur aroma precursors present in beverages, vegetables, fruits, or aromatic herbs like hop but also potentially with some precursors formed through Maillard reactions in cooked foods such as meat or coffee. β-CSLs from microorganisms like yeasts and lactic acid bacteria have been studied for their role in the release of polyfunctional thiols in wine and beer during fermentation. In addition, β-CSLs from microorganisms of the human oral cavity were shown to metabolize similar precursors and to produce aroma in the mouth with an impact on retro-olfaction. This review summarizes the current knowledge on β-CSLs involved in flavor generation with a focus on enzymes from microbial species present either in the fermentative processes or in the oral cavity. This paper highlights the importance of this enzyme family in the food continuum, from production to consumption, and offers new perspectives concerning the utilization of β-CSLs as a flavor enhancer.

Characterization of Key Odor-Active Compounds in Draft Beers for the Chinese Market Using Molecular Sensory Science Approaches

Beer is a popular alcoholic beverage worldwide. However, limited research has been conducted on identifying key odor-active components in lager-type draft beers for the Chinese market. Therefore, this study aims to elucidate the odor characteristics of the four most popular draft beer brands through a sensory evaluation and an electronic nose. Subsequently, the four draft beers were analyzed through solid-phase microextraction and liquid-liquid extraction using a two-dimensional comprehensive gas chromatography-olfactometry-mass spectrometry analysis (GC×GC-O-MS). Fifty-five volatile odor compounds were detected through GC×GC-O-MS. Through an Aroma Extract Dilution Analysis, 22 key odor-active compounds with flavor dilution factors ≥ 16 were identified, with 11 compounds having odor activity values > one. An electronic nose analysis revealed significant disparities in the odor characteristics of the four samples, enabling their distinct identification. These findings help us to better understand the flavor characteristics of draft beer and the stylistic differences between different brands of products and provide a theoretical basis for objectively evaluating the quality differences between different brands of draft beer.

Effects of tea addition on antioxidant capacity, volatiles, and sensory quality of beer

Green tea has great potential to enhance the quality of beer. In this study, green tea was added at different stages of beer brewing, and evaluated the antioxidant capacity, volatile components, as well as sensory quality. The results showed that the addition of green tea during the start of boiling has great potential for application, and the green tea beer (GTB) had remarkable antioxidant properties (ABTS radical scavenging ability, 8.67 mmol TE/L; DPPH radical scavenging ability, 3.97 mmol TE/L; reducing power, 3.28 mmol TE/L), and an excellent sensory quality (acceptance, 6.09/9). HPLC analysis indicated that the principal phenolics in GTB were catechin and caffeic acid, in addition, the relative amounts of ferulic acid, gallic acid can be used to differentiate between GTB and beer. HS-SPME-GC-MS analyses showed that ethyl caprylate, ethyl nonanoate, ethyl caprate, linalool, and phenethyl alcohol were potentially significant for the aroma profile of GTB.

Evaluation of the Antimicrobial Activity of Geraniol and Selected Geraniol Transformation Products against Gram-Positive Bacteria

Both geraniol and the products of its transformation, thanks to their beneficial properties, find a variety of applications in cosmetics. Due to their antioxidant and moisturizing properties, these compounds can be added to skin care products such as face creams, lotions, oils, and masks. In addition, these compounds show some antibacterial and antifungal properties, making them suitable for application in skin care products to help fight against bacteria or fungi. This study determined the antimicrobial activity of geraniol and the compounds which were formed during its transformation in relation to selected Gram-positive bacteria, and the preliminary assessment was made whether these compounds can act as ingredients of preparations with potential antimicrobial activity in the treatment of various human diseases (for example diseases of the skin, digestive system, or urinary tract). In addition, this work presents studies on the microbiological purity of cream samples obtained with different contents of geraniol and its transformation products (contents of the tested compounds: 0.5%, 1.5%, 2.5%, 4%, 8%, and 12%). Antibacterial activity tests were performed using the disc diffusion method against Gram-positive cocci, including the reference strains Staphylococcus aureus ATCC 29213 and Enterococcus faecalis ATCC 29212, and against the clinical strains Staphylococcus aureus MRSA, Staphylococcus epidermidis, Enterococcus faecalis VRE VanB, Enterococcus faecium VRE VanA, and Enterococcus faecium VRE VanB. The most active ingredient against bacteria of the Staphylococcus genus was citral, followed by linalool and then geraniol. During our tests, in the case of bacteria of the Enterococcus genus, citral also showed the highest activity, but linalool, ocimenes, and geraniol showed a slightly lower activity. Moreover, this study examined the microbiological purity of cream samples obtained with various contents of geraniol and its transformation products. In the tests of the microbiological purity of cream samples, no growth of aerobic bacteria and fungi was found, which proves the lack of microbiological contamination of the obtained cosmetic preparations. On this basis, it was assessed that these compounds have preservative properties in the prepared creams. The addition of the analyzed compounds also had influence on the durability of the creams and had no effect on the change in their consistency, did not negatively affect the separation of phases during storage, and even had a positive effect on organoleptic sensations by enriching the smell of the tested samples.

Electrostatic Fermentation: Molecular Response Insights for Tailored Beer Production

Electrostatic fermentation avoids the cellular redox imbalance of traditional fermentation, but knowledge gaps exist. This study explores the impact of electrostatic fermentation on the growth, volatile profile, and genetic response of Saccharomyces pastorianus Saflager S-23. The applied voltage (15 and 30 V) in the electrostatic fermentation system increased the growth and substrate utilization of S. pastorianus while decreasing ethanol production. The aromas typically associated with traditional fermentation, such as alcoholic, grape, apple, and sweet notes, were diminished, while aromas like roses, fruits, flowers, and bananas were augmented in electrostatic fermentation. RNA-seq analysis revealed upregulation of genes involved in cell wall structure, oxidoreductase activity, and iron ion binding, while genes associated with protein synthesis, growth control, homeostasis, and membrane function were downregulated under the influence of applied voltage. The electrostatic fermentation system modulates genetic responses and metabolic pathways in yeast, rendering it a promising method for tailored beer production. Demonstrating feasibility under industrial-scale and realistic conditions is crucial for advancing towards commercialization.

Selecting autochthonous lactic acid bacteria for co-inoculation in Chinese bayberry wine production: Stress response, starter cultures application and volatilomic study

This study focused on isolating and characterising autochthonous lactic acid bacteria (LAB) from spontaneously fermented Chinese bayberry (CB) and their potential application in CB wine fermentation in co-inoculation with yeast starter cultures. Numerous LAB, including Lactiplantibacillus (Lp.) plantarum (9), Limosilactobacillus (Lb.) fermentum (6), Lactococcus (Lc.) lactis (3), Enterococcus (Ec.) hirae (1), Leuconostoc (Le.) mesenteroides (1), and Weissella (Ws.) cibaria (1), were isolated and identified. The isolated strains Lp. plantarum ZFM710 and ZFM715, together with Lb. fermentum ZFM720 and ZFM722, adapted well to unfavourable fermentation environment, including ethanol, osmolality, and acidity stresses, were selected for producing CB wine by co-inoculation with Saccharomyces cerevisiae. During fermentation, the presence of LAB promoted the development of S. cerevisiae, while the population dynamics of LAB in different groups at different stages showed strain-specific differences. Fermentation trials involving LAB yielded a lower ethanol concentration except for Lp. plantarum ZFM715. Compared to the pure S. cerevisiae fermented sample, the addition of LAB led to a clear modulation in organic acid composition. Lb. fermentum strains in co-fermentation led to significant decreases in each classified group of aroma compounds, while Lp. plantarum ZFM715 significantly increased the complexity and intensity of aroma compounds, as well as the intensities of fruity and floral notes. The study selects interesting strains for the design of starter cultures for use in CB wine production, underlining the interest in the selection of autochthonous LAB in fruit wines, with the aim of improving the adaptation of bacteria to specific environmental conditions and shaping the unique traits of the finished products.

Assessment of green lentil malt as a substrate for gluten-free beer brewing

The aim of this study was to analyze whether it is possible to brew beer without using cereals so that the produced beverage could be easily accessible for the population suffering from celiac disease and other gluten-related disorders. Green lentil seeds were malted and then mashed using a congress mashing procedure to assess their advantages and disadvantages in the brewing process. Based on the congress mashing procedure, the mashing process needed to produce beer was developed, and beers were produced from the lentil malts germinated during malting for 96 h, 120 h and 144 h. It was possible to produce beers from the lentil malts; however, they were characterized by a lower alcohol content, lower degree of attenuation and some discrepancies between the concentrations of various volatiles (such as acetaldehyde, ethyl acetate, and 1-propanol) compared to the control beer produced from barley malt.

Chemosensory Characteristics of Brandies from Chinese Core Production Area and First Insights into Their Differences from Cognac

This work aimed to compare the aroma characteristics of representative brandies with different grades from Yantai (one of the Chinese core production areas) and Cognac and to establish relationships between sensory descriptors and chemical composition. Descriptive analysis was performed with a trained panel to obtain the sensory profiles. Forty-three aroma-active compounds were quantified by four different methodologies. A prediction model on the basis of partial least squares analysis was performed to identify candidate compounds that were unique to a certain group of brandies. The result showed that brandies from Yantai could be distinguished from Cognac brandies on the basis of spicy, dried fruit, floral, and fruity-like aromas, which were associated with an aromatic balance between concentrations of a set of compounds such as 5-methylfurfural, γ-nonalactone, and γ-dodecalactone. Meanwhile, brandy with different grades could be distinguished on the basis of compounds derived mostly during the aging process.

Mitigation of microbial nitrogen-derived metabolic hazards as a driver for safer alcoholic beverage choices: An evidence-based review and future perspectives

Alcoholic beverages have been enjoyed worldwide as hedonistic commodities for thousands of years. The unique quality and flavor are attributed to the rich microbiota and nutritional materials involved in fermentation. However, the metabolism of these microbiota can also introduce toxic compounds into foods. Nitrogen-derived metabolic hazards (NMH) are toxic metabolic hazards produced by microorganisms metabolizing nitrogen sources that can contaminate alcoholic beverages during fermentation and processing. NMH contamination poses a risk to dietary safety and human health without effective preventive strategies. Existing literature has primarily focused on investigating the causes of NMH formation, detection methods, and abatement techniques for NMH in fermentation end-products. Devising effective process regulation strategies represents a major challenge for the alcoholic beverage industry considering our current lack of understanding regarding the processes whereby NMH are generated, real-time and online detection, and the high degradation rate after NMH formation. This review summarizes the types and mechanisms of nitrogenous hazard contamination, the potential risk points, and the analytical techniques to detect NMH contamination. We discussed the changing patterns of NMH contamination and effective strategies to prevent contamination at different stages in the production of alcoholic beverages. Moreover, we also discussed the advanced technologies and methods to control NMH contamination in alcoholic beverages based on intelligent monitoring, synthetic ecology, and computational assistance. Overall, this review highlights the risks of NMH contamination during alcoholic beverage production and proposes promising strategies that could be adopted to eliminate the risk of NMH contamination.

Effect of inoculating Pichia spp. starters on flavor formation of fermented chili pepper: Metabolomics and genomics approaches

The influence of Pichia spp. on flavor formation and metabolic pathways during chili pepper fermentation was investigated in this study. Multiple omics approaches were employed, including metabolomics analysis to identify volatile and non-volatile flavor compounds, and genomic analysis to gain insights into the underlying molecular mechanism driving flavor formation of chili peppers inoculated with Pichia spp. The results showed that inoculation with Pichia spp. accelerated fermentation process of chili peppers compared to spontaneous fermentation. Metabolomics analysis showed P. fermentans promoted characteristic terpenes [e.g., (Z)-β-ocimene and linalool], L-glutamate, gamma-aminobutyric acid, and succinate production, while P. manshurica produced more alcohols (e.g., isoamyl alcohol and phenylethyl alcohol) and phenols (e.g., 4-ethylguaiacol and 2-methoxy-4-methylphenol). Genomics analysis revealed that a substantial portion of the genes in Pichia spp. were associated with amino acid and carbohydrate metabolism. Specifically, the pathways involved in amino acid metabolism and the release of glycoside-bound aromatic compounds were identified as the primary drivers behind the unique flavor of fermented chili peppers, facilitated by Pichia spp.

Combined ultrasound and low temperature pretreatment improve the content of anthocyanins, phenols and volatile substance of Merlot red wine

Ultrasound combined with low temperature treatment is a new food processing technology. In this study, low temperature, three ultrasound power levels, and their combinations were adopted in the must before fermentation to study their effects on Merlot red wine. The results showed that ultrasound combined with low temperature pretreatment increased the total and monomer contents of anthocyanins and phenols, affected the color of the wine, and significantly increased its antioxidant capacity. In particular, 240 W of ultrasound combined with low temperature pretreatment reduced the bad odors (caprylic acid, benzaldehyde, and 1-ethanol content) and improved the flower and fruit aroma (1-octanol and phenethyl acetate), as well as the aftertaste, thus improving the quality of the wine. Ultrasound combined with low temperature pretreatment positively affected the quality of Merlot red wine.

Metagenomics and metabolomics of Toddy, an Indian fermented date palm beverage

Toddy is a popular fermented palm beverage of India. No scientific information on shotgun metagenomics and metabolomics are available on toddy of India till date. Hence, we choose the fermented date palm beverage, locally called khejur toddy, of West Bengal and Jharkhand states of India, to profile microbial community, their targeted and untargeted metabolites to study the putative bio-functional genes corresponding to regulatory metabolic pathways. Shotgun-based metataxonomic analyses revealed the existence of all domains where bacteria were the most abundant domain (94.48%) followed by eukaryotes (3.38%), viruses (1.53%) and archaea (0.61%). Overall, 54 phyla, 363 families, 1087 genera and 1885 species were observed and identified. Bacillota (49.3%) was the most abundant bacterial phylum. At species level, several species of bacteria and yeasts were detected in toddy samples which included Leuconostoc mesenteroides,Leuconostoc citreum,Lactobacillus helveticus,Lactiplantibacillus plantarum,Lactococcus lactis, Acetobacter malorum, Gluconobacter japonicus, Gluconacetobacter liquefaciens, Fructobacillus durionis, Zymomonas mobilis and yeastsSaccharomyces cerevisiae, Hanseniaspora uvarumandHanseniaspora guilliermondii. Toddy metagenome was also compared with metagenome of pulque, the Mexican fermented fresh sap ofAgave, which was retrieved from NCBI database, and also with metagenomic data of some amplicon-based previous studies on toddy and African fermented palm drink for similarity, dissimilarity and uniqueness among them. Predictive biosynthesis of ethanol, acetic acid, butanoate, linalool, staurosporine, prodigiosin, folic acid, riboflavin, etc. were annotated by KEGG/COG database. Clustered regularly interspaced short palindromic repeats (CRISPR) analysis detected 23 arrays (average length 23.69 bp ± 4.28). Comprehensive Antibiotic Resistance Database (CARD) analysis did not show the presence of any momentous antibiotic resistance gene among the major microbial members. Metabolomics analysis detected many primary and secondary metabolites. We believe this is the first report on complete shotgun metagenomics, and metabolomics of fermented palm drink of India as well as Eastern India.

Effects of Dry-Hopping on Beer Chemistry and Sensory Properties-A Review

Dry-hopping is the addition of hops to the wort on the cold side of the brewing process. Unlike standard hop additions, its main purpose is not to produce a characteristic bitterness but to extract as much of the hop essential oils as possible, which are largely lost in the standard hopping process. When dry-hopped, it is possible to obtain a beer with an aroma that is difficult to achieve when hops are used on the hot side of the brewing process. As a result, this process has become very popular in recent years, particularly in beers that belong to the 'craft beer revolution' trend. In addition, the usefulness of this process is increasing with the development of new hop varieties with unique aromas. This article presents the main components of hops, focusing on those extracted during the process. Changes in the composition of beer bittering compounds and essential oils resulting from this process are discussed. This paper presents the current state of the knowledge on the factors affecting the degree of extraction, such as hop dosage, the time, and temperature of the process. Issues such as process-related physicochemical changes, hop creep, low flavor stability, haze formation, and green flavor are also discussed.

Assessment of the impact of unmalted cereals, hops, and yeast strains on volatolomic and olfactory profiles of Blanche craft beers: A chemometric approach

This study investigated the impact of changes in craft beer formulation, by modifying the unmalted cereal [(durum (Da) and soft (Ri) wheat), emmer (Em)], hops [Cascade (Ca) and Columbus (Co)], and yeast strains [M21 (Wi) - M02 (Ci)], on volatolomic, acidic, and olfactory profiles. Olfactory attributes were evaluated by the trained panel. Volatolomic and acidic profiles were determined by GC-MS. The sensory analysis detected significant differences for 5 attributes, including olfactory intensity and finesse, malty, herbaceous, and floral notes. Multivariate analysis of volatiles data, showed significant differences among the samples (p < 0.05). DaCaWi, DaCoWi, and RiCoCi beers differ from the others by their higher concentrations of esters, alcohols, and terpenes. A PLSC analysis was carried out between volatiles and odour attributes. As far as we know, this is the first investigation that shed light on the impact of 3-factors interaction on the sensory-volatolomic profile of craft beers, through a comprehensive multivariate approach.

Aroma Profile Development in Beer Fermented with Azacca, Idaho-7, and Sultana Hops

Hops are among the most costly and environmentally impactful raw materials used in brewing, yet they play a crucial role in the aroma of beer. However, predicting beer aroma based on hop variety or hopping method remains arduous. This is partly because hop oils are unique for each hop variety, and they may be biotransformed by yeast enzymes during fermentation. Even slight molecular structure modifications can dramatically affect the organoleptic properties of beer. Through combined chemical and sensory analysis of dry-hopped beers prepared with different hop varieties (Azacca, Idaho-7, and Sultana), this work aimed to profile the aromas and the overall biotransformation processes taking place during fermentation. A total of 51 volatile organic compounds (VOCs) were semi-quantified and monitored: 19 esters, 13 sesquiterpenes, 7 ketones, 7 alcohols, 4 monoterpenes, and 1 volatile acid. There were significant similarities in the measured analytes and perceived aromas of these beers, but one hop variety (Sultana) delivered an increased quantity of unique aromas and an increased concentration of volatiles in the headspace for the same quantity of hop pellets added. This work provides practical information to brewers who utilize hops in beer production.

Impact of the acquired subgenome on the transcriptional landscape in Brettanomyces bruxellensis allopolyploids

Gene expression variation can provide an overview of the changes in regulatory networks that underlie phenotypic diversity. Certain evolutionary trajectories such as polyploidization events can have an impact on the transcriptional landscape. Interestingly, the evolution of the yeast species Brettanomyces bruxellensis has been punctuated by diverse allopolyploidization events leading to the coexistence of a primary diploid genome associated with various haploid acquired genomes. To assess the impact of these events on gene expression, we generated and compared the transcriptomes of a set of 87 B. bruxellensis isolates, selected as being representative of the genomic diversity of this species. Our analysis revealed that acquired subgenomes strongly impact the transcriptional patterns and allow discrimination of allopolyploid populations. In addition, clear transcriptional signatures related to specific populations have been revealed. The transcriptional variations observed are related to some specific biological processes such as transmembrane transport and amino acids metabolism. Moreover, we also found that the acquired subgenome causes the overexpression of some genes involved in the production of flavor-impacting secondary metabolites, especially in isolates of the beer population.

Unravelling the hidden power of esterases for biomanufacturing of short-chain esters

Microbial production of esters has recently garnered wide attention, but the current production metrics are low. Evidently, the ester precursors (organic acids and alcohols) can be accumulated at higher titers by microbes like Escherichia coli. Hence, we hypothesized that their 'direct esterification' using esterases will be efficient. We engineered esterases from various microorganisms into E. coli, along with overexpression of ethanol and lactate pathway genes. High cell density fermentation exhibited the strains possessing esterase-A (SSL76) and carbohydrate esterase (SSL74) as the potent candidates. Fed-batch fermentation at pH 7 resulted in 80 mg/L of ethyl acetate and 10 mg/L of ethyl lactate accumulation by SSL76. At pH 6, the total ester titer improved by 2.5-fold, with SSL76 producing 225 mg/L of ethyl acetate, and 18.2 mg/L of ethyl lactate, the highest reported titer in E. coli. To our knowledge, this is the first successful demonstration of short-chain ester production by engineering 'esterases' in E. coli.

Involvement of a flavoprotein, acetohydroxyacid synthase, in growth and riboflavin production in riboflavin-overproducing Ashbya gossypii mutant

BACKGROUND

Previously, we isolated a riboflavin-overproducing Ashbya gossypii mutant (MT strain) and discovered some mutations in genes encoding flavoproteins. Here, we analyzed the riboflavin production in the MT strain, in view of flavoproteins, which are localized in the mitochondria.

RESULTS

In the MT strain, mitochondrial membrane potential was decreased compared with that in the wild type (WT) strain, resulting in increased reactive oxygen species. Additionally, diphenyleneiodonium (DPI), a universal flavoprotein inhibitor, inhibited riboflavin production in the WT and MT strains at 50 µM, indicating that some flavoproteins may be involved in riboflavin production. The specific activities of NADH and succinate dehydrogenases were significantly reduced in the MT strain, but those of glutathione reductase and acetohydroxyacid synthase were increased by 4.9- and 25-fold, respectively. By contrast, the expression of AgGLR1 gene encoding glutathione reductase was increased by 32-fold in the MT strain. However, that of AgILV2 gene encoding the catalytic subunit of acetohydroxyacid synthase was increased by only 2.1-fold. These results suggest that in the MT strain, acetohydroxyacid synthase, which catalyzes the first reaction of branched-chain amino acid biosynthesis, is vital for riboflavin production. The addition of valine, which is a feedback inhibitor of acetohydroxyacid synthase, to a minimal medium inhibited the growth of the MT strain and its riboflavin production. In addition, the addition of branched-chain amino acids enhanced the growth and riboflavin production in the MT strain.

CONCLUSION

The significance of branched-chain amino acids for riboflavin production in A. gossypii is reported and this study opens a novel approach for the effective production of riboflavin in A. gossypii.

Identification and assessment of non-conventional yeasts in mixed fermentations for brewing bioflavored beer

The increasing demand for more flavored and complex beers encourages the investigation of novel and non-conventional yeasts with the ability to provide a combination of bioflavoring and low ethanol yields. The present study identified 22 yeasts isolated from different brewing sources, including the fermentation by-products known as yeast sludges, and characterized a selection of strains to find the more suitable for the aforementioned aims. HPLC and GC-FID analysis of its brewing products were performed. The most promising results were obtained with the non-conventional yeasts Pichia kudriavzevii MBELGA61 and Meyerozyma guilliermondii MUS122. The former, isolated from a Belgian wheat beer sludge, was capable of growing in wort (17.0°Bx., 20 °C) with very low ethanol yields (1.19 % v/v). Besides, upon mixed fermentations with Saccharomyces cerevisiae, was suitable to produce volatile compounds such as ethyl acetate, 2-phenyl ethanol and isoamyl alcohol, with characteristic fruity notes. M. guilliermondii MUS122, isolated from a golden ale beer sludge, partially attenuated the wort with low production of ethanol and biomass. In addition, provided some fruity and floral nuances to the aroma profile of mixed fermentations with brewer's yeast. The results suggest that these strains favor the development of more fruity-flowery aroma profiles in beers. Furthermore, they are suitable for use in mixed fermentations with Saccharomyces brewer's strains, although the ethanol level did not decrease significantly.

The bio3 mutation in sake yeast leads to changes in organic acid profiles and ester levels but not ethanol production

Biotin is an essential coenzyme that is bound to carboxylases and participates in fatty acid synthesis. The fact that sake yeast exhibit biotin prototrophy while almost all other Saccharomyces cerevisiae strains exhibit biotin auxotrophy, implies that biotin prototrophy is an important factor in sake brewing. In this study, we inserted a stop codon into the biotin biosynthetic BIO3 gene (cording for 7,8-diamino-pelargonic acid aminotransferase) of a haploid sake yeast strain using the marker-removable plasmid pAUR135 and investigated the fermentation profile of the resulting bio3 mutant. Ethanol production was not altered when the bio3 mutant was cultured in Yeast Malt (YM) medium containing 10% glucose at 15 °C and 30 °C. Interestingly, ethanol production was also not changed during the sake brewing process. On the other hand, the levels of organic acids in the bio3 mutant were altered after culturing in YM medium and during sake brewing. In addition, ethyl hexanoate and isoamyl acetate levels decreased in the bio3 mutant during sake brewing. Metabolome analysis revealed that the decreased levels of fatty acids in the bio3 mutant were attributed to the decreased levels of ethyl hexanoate. Further, the transcription level of genes related to the synthesis of ethyl hexanoate and isoamyl acetate were significantly reduced. The findings indicated that although the decrease in biotin biosynthesis did not affect ethanol production, it did affect the synthesis of components such as organic acids and aromatic compounds. Biotin biosynthesis ability is thus a key factor in sake brewing.

The combination of omics strategies to evaluate starter and probiotic strains in the Catharina sour Brazilian-style beer

Catharina sour, the first internationally recognized Brazilian beer, is characterized by fermentation with lactic acid bacteria (LAB), which may have probiotic potential, and the addition of fruit juice. This study aimed to evaluate the use of the starter Streptococcus thermophilus TH-4 (TH-4) and the probiotics Lacticaseibacillus paracasei F19 and 431, associated with Saccharomyces cerevisiae US-05, in the absence (control)/presence of passion fruit or peach juices. Evaluation proceeded during fermentation and storage by enumeration using pour-plate and qPCR; gene expressions of hop resistance; proteome by Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS); and odor, flavor, and metabolome by Headspace Solid-Phase Microextraction (HS-SPME), coupled with the gas chromatography-mass spectrometry (GC-MS) analysis. We concluded that the strains studied are recommended for applications in sour beers, due to the presence of defense mechanisms like membrane adhesion and H + pump. Furthermore, HS-SPME/GC-MS indicated that the strains may contribute to the beer flavor and odor.

Production and sensory analysis of grape flavoured beer by co-fermentation of an industrial and a genetically modified laboratory yeast strain

The so-called "craft beer revolution" has increased the demand for new styles of beers, often with new ingredients like flavour extracts. In recent years, synthetic biology has realized the production of a plethora of plant secondary metabolites in microbial hosts, which could provide an alternative source for these compounds. In this study, we selected a in situ flavour production approach for grape flavour addition. We used an O-methyl anthranilate (OmANT) producing laboratory Saccharomyces cerevisiae strain in co-fermentations with an industrial beer yeast strain WLP644. The laboratory strain provided an ease of genetic manipulation and the desirable properties of the WLP644 strain were not modified in this approach. In shake flasks, a 10:90 ratio of the yeasts produced grape flavoured beer with the yeast produced flavour compound in a range normally used for flavoured beverages. Hopped and unhopped beers were analysed by VTT's trained sensory panel and with olfactory GC-MS. OmANT was successfully detected from the beers as a floral odour and flavour. Moreover, no off-flavours were detected and aroma profiles outside the grape flavour were rather similar. These results indicate that the co-fermentation principle is a suitable approach to change the flavour profiles of beers with a simple yeast strain drop-in approach.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00217-023-04274-1.

Genome-wide analysis reveals Hsf1 maintains high transcript abundance of target genes controlled by strong constitutive promoter in Saccharomyces cerevisiae

BACKGROUND

In synthetic biology, the strength of promoter elements is the basis for precise regulation of target gene transcription levels, which in turn increases the yield of the target product. However, the results of many researches proved that excessive transcription levels of target genes actually reduced the yield of the target product. This phenomenon has been found in studies using different microorganisms as chassis cells, thus, it becomes a bottleneck problem to improve the yield of the target product.

RESULTS

In this study, promoters PGK1p and TDH3p with different strengths were used to regulate the transcription level of alcohol acetyl transferase encoding gene ATF1. The results demonstrated that the strong promoter TDH3p decreased the production of ethyl acetate. The results of Real-time PCR proved that the transcription level of ATF1 decreased rapidly under the control of TDH3p, and the unfolded protein reaction was activated, which may be the reason for the abnormal production caused by the strong promoter. RNA-sequencing analysis showed that the overexpression of differential gene HSP30 increased the transcriptional abundance of ATF1 gene and production of ethyl acetate. Interestingly, deletion of the heat shock protein family (e.g., Hsp26, Hsp78, Hsp82) decreased the production of ethyl acetate, suggesting that the Hsp family was also involved in the regulation of ATF1 gene transcription. Furthermore, the results proved that the Hsf1, an upstream transcription factor of Hsps, had a positive effect on alleviating the unfolded protein response and that overexpression of Hsf1 reprogramed the pattern of ATF1 gene transcript levels. The combined overexpression of Hsf1 and Hsps further increased the production of ethyl acetate. In addition, kinase Rim15 may be involved in this regulatory pathway. Finally, the regulation effect of Hsf1 on recombinant strains constructed by other promoters was verified, which confirmed the universality of the strategy.

CONCLUSIONS

Our results elucidated the mechanism by which Rim15-Hsf1-Hsps pathway reconstructed the repression of high transcription level stress and increased the production of target products, thereby providing new insights and application strategies for the construction of recombinant strains in synthetic biology.

Evaluation of volatile compound profiles and sensory properties of dark and pale beers fermented by different strains of brewing yeast

To evaluate the differences in the volatile compound profile of dark and pale beers fermented by different strains of brewer's yeast, gas chromatography with flame ionization detection and gas chromatography mass spectrometry analysis of eight beers was carried out. The prevalent group of compounds in all the beers analysed were alcohols (56.41-72.17%), followed by esters (14.58-20.82%), aldehydes (8.35-20.52%), terpenes and terpenoids (1.22-6.57%) and ketones (0.42-1.00%). The dominant higher alcohols were 2-methylpropan-1-ol, 3-methylbutanol, phenethyl alcohol, among aldehydes furfural, decanal, nonanal, and among esters ethyl acetate, phenylethyl acetate and isoamyl acetate. Beers fermented by the top-fermenting yeast Saccharomyces cerevisiae var. diastaticus had the highest volatile content. The addition of dark malt in wort production process had no effect on the total content of volatiles, but for some beers it caused changes in the total content of esters, terpenes and terpenoids. Variations in the total volatile content between beers fermented by different yeast strains are mainly due to esters and alcohols identified. Sensory analysis of beers allowed us to identify the characteristics affected by the addition of dark speciality malts in the production of wort and yeast strains used in the fermentation process.

Brewing a Craft Belgian-Style Pale Ale Using Pichia kudriavzevii 4A as a Starter Culture

There is an expanding market for beer of different flavors. This study aimed to prepare a craft Belgian-style pale ale with a non-Saccharomyces yeast. Pichia kudriavzevii 4A was used as a sole starter culture, and malted barley as the only substrate. The ingredients and brewing process were carefully monitored to ensure the quality and innocuousness of the beverage. During fermentation, the yeast consumed 89.7% of total sugars and produced 13.8% v/v of ethanol. The product was fermented and then aged for 8 days, adjusted to 5% v/v alcohol, and analyzed. There were no traces of mycotoxins, lead, arsenic, methanol, or microbiological contamination that would compromise consumer health. According to the physicochemical analysis, the final ethanol concentration (5.2% v/v) and other characteristics complied with national and international guidelines. The ethyl acetate and isoamyl alcohol present are known to confer sweet and fruity flavors. The sensory test defined the beverage as refreshing and as having an apple and pear flavor, a banana aroma, and a good level of bitterness. The judges preferred it over a commercial reference sample of Belgian-style pale ale made from S. cerevisiae. Hence, P. kudriavzevii 4A has the potential for use in the beer industry.

Investigation of Geraniol Biotransformation by Commercial Saccharomyces Yeast Strains by Two Headspace Techniques: Solid-Phase Microextraction Gas Chromatography/Mass Spectrometry (SPME-GC/MS) and Proton Transfer Reaction-Time of Flight-Mass Spectrometry (PTR-ToF-MS)

Hop-derived volatile organic compounds (VOCs) and their transformation products significantly impact beer flavour and aroma. Geraniol, a key monoterpene alcohol in hops, has been reported to undergo yeast-modulated biotransformation into various terpenoids during fermentation, which impacts the citrus and floral aromas of the finished beer. This study monitored the evolution of geraniol and its transformation products throughout fermentation to provide insight into differences as a function of yeast species and strain. The headspace concentration of VOCs produced during fermentation in model wort was measured using Solid-Phase Microextraction Gas Chromatography/Mass Spectrometry (SPME-GC/MS) and Proton Transfer Reaction-Time of Flight-Mass Spectrometry (PTR-ToF-MS). In the absence of yeast, only geraniol was detected, and no terpenoid compounds were detected in geraniol-free ferments. During fermentation, the depletion of geraniol was closely followed by the detection of citronellol, citronellyl acetate and geranyl acetate. The concentration of the products and formation behaviour was yeast strain dependent. SPME-GC/MS provided confidence in compound identification. PTR-ToF-MS allowed online monitoring of these transformation products, showing when formation differed between Saccharomyces cerevisiae and Saccharomyces pastorianus yeasts. A better understanding of the ability of different yeast to biotransform hop terpenes will help brewers predict, control, and optimize the aroma of the finished beer.

Novel Saccharomyces cerevisiae × Saccharomyces mikatae Hybrids for Non-alcoholic Beer Production

The popularity of non-alcoholic beers has been increasing over the past few years. Maltose-negative strains of different genera are frequently used to obtain beers of low alcohol content. S. cerevisiae hybrids with other Saccharomyces species offer interesting inherited flavour characteristics; however, their use in non-alcoholic beer production is rare. In this work, we constructed six hybrids of maltose-negative S. cerevisiae parental strains (modified to produce higher amounts of organic acids) and S. mikatae (wild-type). Growth behaviour, osmotolerance and fermentation features of the offspring were compared with parental strains. One hybrid with mitochondrial DNA inherited from both parents was used to produce non-alcoholic beer in which organic metabolites were evaluated by HPLC and HS-SPME-GC-MS. This hybrid produced non-alcoholic beer (≤0.05% (v/v)) with an increased organic acid content, just as its parent S. cerevisiae, but without producing increased amounts of acetic acid. The beer had a neutral aromatic profile with no negative off-flavours, similar to the beer produced by the parent S. mikatae, which was used for the first time to produce non-alcoholic beer. Overall, both parents and hybrid yeast produced non-alcoholic beers with increased amounts of higher alcohols compared with esters.

Impact of Assimilable Nitrogen Supplementation on Saccharomyces cerevisiae Metabolic Response and Aromatic Profile of Moschofilero Wine

The concentration of nitrogen in must is critical to yeast fermentation efficiency and wine aroma profile. The present work determined the effect of the amount of yeast assimilable nitrogen (YAN) on fermentation kinetics, aroma production, and gene expression patterns of the wine yeast Saccharomyces cerevisiae. Fermentations were performed under two different YAN concentrations of must. Acetate esters, linalool, and nerol appeared to be clearly affected by the different YAN levels. Real-time-PCR results revealed that the genes involved in ethyl and acetate esters production recorded, in general, higher transcript levels under high nitrogen supplementation. In addition, an up-regulation of the BGL2 and EXG1 genes, which are related to terpenes production, was observed in the case of high nitrogen content and it is well corresponded to the terpenol concentration found. Our study revealed the impact of nitrogen supplementation on yeast metabolism and its importance to adjust wine's aromatic composition and sensory profile.

Examining How the Fermentation Medium Influences Thiol Expression and Its Perceived Aroma in Commercial Brewing Yeast Strains

In Saccharomyces, the IRC7 gene encodes for a cysteine S-conjugate β-lyase enzyme which can release polyfunctional thiols from their cysteinylated precursor forms, thereby promoting thiol aroma in beer. This study examined the thiol production of 10 commercial yeast strains in two different media, a hopped yeast extract-peptone-dextrose (YPD) medium and a 100% barley malt wort to explore how differences in yeast strain and medium conditions influence the release of polyfunctional thiols. 3-Sulfanylhexan-1-ol was most affected by medium conditions, and its concentrations were highest in wort fermentations. The higher nitrogen content and pH of the YPD medium relative to the wort fermentations were notable differences, and significant correlations between these variables and the extent of free thiol production were observed. A strong association existed between polyfunctional thiol concentrations and the fermentation-derived, malt, and hop-derived compounds 2-phenylethanol, β-damascenone, and β-ionone. The sensory impressions of thiol character in beer were influenced by the presence of other aromatic compounds such as esters and terpene alcohols, and aroma attributes such as "tropical" were not the most suitable for describing beers brewed with yeasts that fully express homozygous IRC7^F. Sensory attributes "sweaty", "vegetal", and "overripe fruit" were more strongly associated with these strains.

Technological properties and composition of volatile compounds in winter wheat malts grown with addition of seed meals into soil

Wheat malts are necessary to produce wheat beers. In this study, wheat was grown with addition of seed meals into the soil, to determine whether such agricultural practice could improve the quality of the grain and, therefore, improve the quality of wheat malt produced from these grains. It was determined, that malt produced from the grains of the winter wheat cultivated with the use of seed meals is characterised with improved technological properties, such as saccharification time, filtration time and extract content and some of the seed meals had a positive impact on the content of various volatile compounds present in the produced malts.

Identification and validation of core microbes associated with key aroma formation in fermented pepper paste (Capsicum annuumL.)

Fermented peppers are usually obtained by the spontaneous fermentation of microorganisms attached to fresh peppers, and the variable microbial composition would lead to inconsistencies in flavor between batches. To demonstrate the roles of microorganisms in flavor formation, the core microbes closely associated with the key aroma compounds of fermented pepper paste were screened and validated in this study. Lactobacillus was the dominant bacterial genus in fermented pepper paste, whereas the main fungal genera were Alternaria and Kazachstania. Nine strains of the genera Lactobacillus, Weissella, Bacillus, Zygosaccharomyces, Kazachstania, Debaryomyces, and Pichia were isolated from fermented pepper paste. Eleven key aroma compounds were identified using gas chromatography combined with olfactometry and relative odor activity values. Correlation analysis showed that Zygosaccharomyces and Kazachstania were positively correlated with the majority of the key aroma compounds, whereas Lactobacillus was negatively correlated with them. Thus, Zygosaccharomyces and Kazachstania were identified as core genera associated with the key odorants. Finally, Zygosaccharomyces bisporus, Kazachstania humilis, and Lactiplantibacillus plantarum were used as starter cultures for fermented peppers, confirming that Z. bisporus and K. humilis were more beneficial for the key aroma compounds (e.g., acetate, linalool, and phenyl ethanol) rather than L. plantarum. This study contributed to understanding the flavor formation mechanism and provided references for the quality control of food fermentation.

Use of Mixed Cultures for the Production of Grape–Plum Low-Alcohol Fermented Beverages

This work presents the attempt to develop a production technology for grape–plum low-alcohol beverages and enhance their chemical composition and flavor complexity through the non-Saccharomyces species. Saccharomyces cerevisiae (SC) pure cultures were used as reference beverages. Pure cultures of Lachancea thermotolerans (LT) and co-inoculated Lachancea thermotolerans with Saccharomyces cerevisiae (MIX) were included for grape–plum must fermentation at a pilot scale. The process involves two steps: a primary alcoholic fermentation in stainless steel tanks (F1) and a secondary fermentation in a bottle after dextrose syrup addition (F2). The chemical compositions of all beverages obtained in F1 and F2 were studied. Compared to SC, must inoculated with L. thermotolerans (LT and MIX) required four more days to complete the fermentation of sugars during F1. SC fermentation tended to have slightly higher pH and titratable acidity values and lower concentrations of total phenols. Final levels of aromatic precursor nitrogen and sulfur amino nitrogen were obtained more in SC than in LT and MIX. SC treatment had higher final levels of histidine, phenylalanine, isoleucine, lysine, methionine, threonine, valine, and cysteine. Related to individual amino acids, SC treatment had higher final levels of histidine, phenylalanine, isoleucine, lysine, methionine, threonine, valine, and cysteine. Analysis of the volatile composition showed that, compared with SC, MIX had the highest percentage of higher alcohols (3-methyl-1-butanol and 2-methyl-1-butanol) and acetates (isoamyl acetate and isobutyl acetate) which are associated with fruity and banana aromas. A decreasing trend in volatile fatty acids was observed in LT and MIX compared to SC. LT application, both in pure and mixed culture, significantly modified the values of the percentage of 5 of the 10 ethyl ester compounds analyzed. Finally, the sensory analysis showed that there were no significant differences, even though the non-Saccharomyces had a higher percentage of volatile metabolites. The results have shown that through this process an innovative and high-quality product was obtained: a low-alcohol beverage made from grapes and plums, which could be developed at an industrial level due to the increasing interest of consumers in this type of product.

Development of sake yeast breeding and analysis of genes related to its various phenotypes

Sake is a traditional Japanese alcoholic beverage made from rice and water, fermented by the filamentous fungi Aspergillus oryzae and the yeast Saccharomyces cerevisiae. Yeast strains, also called sake yeasts, with high alcohol yield and the ability to produce desired flavor compounds in the sake, have been isolated from the environment for more than a century. Furthermore, numerous methods to breed sake yeasts without genetic modification have been developed. The objectives of breeding include increasing the efficiency of production, improving the aroma and taste, enhancing safety, imparting functional properties, and altering the appearance of sake. With the recent development of molecular biology, the suitable sake brewing characteristics in sake yeasts, and the causes of acquisition of additional phenotypes in bred yeasts have been elucidated genetically. This mini-review summarizes the history and lineage of sake yeasts, their genetic characteristics, the major breeding methods used, and molecular biological analysis of the acquired strains. The data in this review on the metabolic mechanisms of sake yeasts and their genetic profiles will enable the development of future strains with superior phenotypes.

Versatility of Saccharomyces cerevisiae 41CM in the Brewery Sector: Use as a Starter for “Ale” and “Lager” Craft Beer Production

Craft breweries tend to use special raw materials and also special ingredients (spices, herbs, fruits) to typify beers, but the metabolic activities of yeasts play a primary role in defining the sensory characteristics of this beverage. Saccharomyces cerevisiae and Saccharomyces pastorianus are yeast species usually used for ale and lager beer production. The selection and use of new yeast starters with peculiar technological and enzymatic characteristics could represent the key point for the production of beers with good and distinctive organoleptic properties. In this study, the fermentative performance of S. cerevisiae 41CM yeast isolated from the vineyard environment for ale and lager craft beer production on a laboratory scale was evaluated. The commercial yeast S. cerevisiae Fermentis S-04 and S. pastorianus Weihenstephan 34/70 were used as reference strains. S. cerevisiae 41CM showed fermentative kinetics similar to commercial starters, both in lager (12 °C) and ale (20 °C) brewing. In all beers brewed, the largest percentage of volatile compounds synthesized during the fermentation were alcohols, followed by esters, terpenes, and aldehydes. In particular, S. cerevisiae 41CM starter contributed a higher relative percentage of esters in the ale beer than that detected in the lager beer, without ever synthesizing unwanted volatile compounds.

Non-Conventional Yeast: Behavior under Pure Culture, Sequential and Aeration Conditions in Beer Fermentation

The use of wild yeasts, isolated from different environments, is becoming the most interesting option for the production of new beers. The objective of this study is to evaluate the potential of seven non-conventional yeast strains from five different species (Saccharomyces cerevisiae, Hanseniaspora guilliermondii, Metschnikowia pulcherrima, Torulaspora delbrueckii, and Zygosaccharomyces bailii) isolated from Madrid agriculture to produce type ale beer. Wild yeast strains were evaluated at laboratory and pilot plant scales under different fermentation conditions (pure, aerated, and sequential culture). Strain S. cerevisiae SafAle S-04 was used as a reference. Throughout the fermentation of beer, volatile compounds were determined by GC and residual sugars by HPLC, among other parameters. The yeast strains used for the fermentation in pure culture conditions were unable to ferment maltose and maltotriose (0.73-1.18% v/v of ethanol). The results of the study under aerated conditions showed varying levels of higher alcohol and ester concentrations. It should be noted that the strain CLI 1057 (S. cerevisiae) fermented maltose in the presence of oxygen (Kluyver effect). This strain also showed a high production of 4-vinyl guaiacol, making it suitable for producing beers with a phenolic profile. Finally, three strains (H. guilliermondii, Z. bailii, and T. delbrueckii) were evaluated in sequential culture together with commercial strain and found to improve the organoleptic characteristics of the brewed beer. These approaches offer the opportunity to add new product characteristics to the beers.

Effect of Hop Varieties and Forms in the Hopping Process on Non-Alcoholic Beer Quality

The aim of this study was to determine how the hopping technique affects the quality of non-alcoholic beer (NAB). A series of NABs were brewed and tested for basic physicochemical characteristics, profiles of selected volatile compounds, and microbial contamination. The brewing process yielded 13 experimental groups of beers, all of which had an ethanol content of <0.5%v/v. Among the batches brewed with ‘Marynka’ hops, the pellet form was found to provide the highest concentrations of hop-derived volatile compounds, whereas in the ‘Magnum’ groups, the extracts and whole hops proved superior. Humulene and caryophyllene were the primary volatiles in terms of quantity. All the brews were contamination-free—no microbes other than yeast cells were detected. Their microbiological purity was also supported by an assay of beer-defect indicators (volatile compounds), which only showed low levels of acetaldehyde, 1-propanol, 2-methylbutanol, and 3-methylbutanol. The hopping technique deployed was found not to affect the physicochemical parameters of NABs, but did have a significant impact on their volatile compound profile.

Schizosaccharomyces pombe in the Brewing Process: Mixed-Culture Fermentation for More Complete Attenuation of High-Gravity Wort

High-gravity brewing is a method that maximises brewhouse capacity and reduces energy consumption per unit of beer produced. The fermentation of wort with high sugar content is known to impact the fermentation characteristics and production of aroma-active volatiles, and as such, cultures that are adapted to this method are industrially valuable. Mixed-culture fermentation offers brewers the opportunity to combine desirable features from multiple strains of yeast and to take advantage of the interactions between those strains. In this study, a highly attenuative strain of Schizosaccharomyces pombe is paired with a fast-fermenting brewing strain of Saccharomyces cerevisiae in the fermentation of wort at both standard and high gravity at centilitre scale. Mixed cultures were found to produce several esters and higher alcohols in higher concentration than in either of the parent monocultures at both standard and high gravity. The mixed culture also represented a compromise between fermentation length (modelled by the logistic equation), which was extended by the inclusion of S. pombe, and ethanol yield, which was increased. The application of mixed-culture strategies to high-gravity brewing practices may allow brewers greater flexibility in achieving desired flavour profiles whilst increasing brewhouse efficiency.

Adaptive evolution in the Saccharomyces kudriavzevii Aro4p promoted a reduced production of higher alcohols

The use of unconventional yeast species in human-driven fermentations has attracted a lot of attention in the last few years. This tool allows the alcoholic beverage industries to solve problems related to climate change or the consumer demand for newer high-quality products. In this sense, one of the most attractive species is Saccharomyces kudriavzevii, which shows interesting fermentative traits such as the increased and diverse aroma compound production in wines. Specifically, it has been observed that different isolates of this species can produce higher amounts of higher alcohols such as phenylethanol compared with Saccharomyces cerevisiae. In this work, we have shed light on this feature relating it to the S. kudriavzevii aromatic amino acid anabolic pathway in which the enzyme Aro4p plays an essential role. Unexpectedly, we observed that the presence of the S. kudriavzevii ARO4 variant reduces phenylethanol production compared with the S. cerevisiae ARO4 allele. Our experiments suggest that this can be explained by increased feedback inhibition, which might be a consequence of the changes detected in the Aro4p amino end such as L₂₆ Q₂₄ that have been under positive selection in the S. kudriavzevii specie.

Increased volatile thiol release during beer fermentation using constructed interspecies yeast hybrids

Interspecies hybridization has been shown to be a powerful tool for developing and improving brewing yeast in a number of industry-relevant respects. Thanks to the popularity of heavily hopped ‘India Pale Ale’-style beers, there is an increased demand from brewers for strains that can boost hop aroma. Here, we explored whether hybridization could be used to construct strains with an enhanced ability to release hop-derived flavours through β-lyase activity, which releases desirable volatile thiols. Wild Saccharomyces strains were shown to possess high β-lyase activity compared to brewing strains, however, they also produced phenolic off-flavours (POF) and showed poor attenuation. To overcome these limitations, interspecies hybrids were constructed by crossing pairs of one of three brewing and one of three wild Saccharomyces strains (S. uvarum and S. eubayanus). Hybrids were screened for fermentation ability and β-lyase activity, and selected hybrids showed improved fermentation and formation of both volatile thiols (4MMP, 3MH and 3MH-acetate) and aroma-active esters compared to the parent strains. Undesirable traits (e.g. POF) could be removed from the hybrid by sporulation. To conclude, it was possible to boost the release of desirable hop-derived thiols in brewing yeast by hybridization with wild yeast. This allows production of beer with boosted hop aroma with less hops (thus improving sustainability issues).