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

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).

The Sensorial and Chemical Changes in Beer Brewed with Yeast Genetically Modified to Release Polyfunctional Thiols from Malt and Hops

The biotransformation of hop aroma, particularly by the cysteine S-conjugate beta-lyase enzyme (CSL), has been a recent topic of tremendous interest among brewing scientists and within the brewing community. During a process often referred to as biotransformation, yeast-encoded enzymes convert flavorless precursor molecules found in barley and hops into volatile thiols that impart a variety of desirable flavors and aromas in beer. Two volatile thiols of particular interest are 3-mercaptohexan-1-ol (3MH) and its acetate ester, 3-mercaptohexyl acetate (3MHA), which impart guava and passionfruit flavors, respectively. In this study, a parental Saccharomyces cerevisiae brewing strain that displayed low thiol biotransformation activity was genetically manipulated (GM) to substantially increase its thiol biotransformation potential. Construction of this GM strain involved integration of a gene encoding a highly active CSL enzyme that converts thiol precursors into the volatile thiol, 3MH. Three additional strains were subsequently developed, each of which paired CSL expression with expression of an alcohol acyltransferase (AAT) gene. It was hypothesized that expression of an AAT in conjunction with CSL would increase production of 3MHA. Fermentation performance, sensory characteristics, and 3MH/3MHA production were evaluated for these four GM strains and their non-GM parent in 1.5hL fermentations using 100% barley malt wort hopped at low levels with Cascade hops. No significant deviations in fermentation performance (time to attenuation, final gravity, alcohol content, wort fermentability) or finished beer chemistry were observed between the GM strains and the parent strain with the exception of the speed of vicinal diketones reduction post-fermentation, which was quicker for the GM strains. The GM strains produced beer that had up to 73-fold and 8-fold higher 3MH and 3MHA concentrations than the parent strain, achieving concentrations that were up to 79-fold greater than their sensory detection thresholds. The beers were described as intensely tropical and fruity, and were associated with guava, passionfruit, mango, pineapple and sweaty aromas. These experiments demonstrate the potential of genetic modification to dramatically enhance yeast biotransformation ability without creating off flavors or affecting fermentation performance.

Potential of non-Saccharomyces yeast to produce non-alcoholic beer

Recently, non-Saccharomyces yeast have become very popular in wine and beer fermentation. Their interesting abilities introduce novel aromatic profiles to the fermented product. In this study, screening of eight non-Saccharomyces yeast (Starmerella bombicola, Lindnera saturnus, Lindnera jadinii, ZygoSaccharomyces rouxii, Torulaspora delbrueckii, Pichia kluyveri, Candida pulcherrima, and Saccharomycodes ludwigii) revealed their potential in non-alcoholic beer production. Conditions for non-alcoholic beer production were optimised for all strains tested (except T. delbrueckii) with the best results obtained at temperature 10 to 15 °C for maximum of 10 days. Starmerella bombicola, an important industrial producer of biosurfactants, was used for beer production for the first time and was able to produce non-alcoholic beer even at 20 °C after 10 days of fermentation. Aromatic profile of the beer fermented with S. bombicola was neutral with no negative impact on organoleptic properties of the beer. The most interesting organoleptic properties were evaluated in beers fermented with L. jadinii and L. saturnus, which produced banana-flavoured beers with low alcohol content. This work confirmed the suitability of mentioned yeast to produce non-alcoholic beers and could serve as a steppingstone for further investigation.

Fruit Microbial Communities of the Bisucciu Sardinian Apricot Cultivar (Prunus armeniaca L.) as a Reservoir of New Brewing Starter Strains

Local fruit cultivars may improve the originality of specialty beers both directly, by conferring peculiar tastes and flavors, and indirectly, as a reservoir of new starter strains. Accordingly, the fungal and bacterial communities of Bisucciu fruit, a Sardinian apricot cultivar used to produce a local fruit beer, were here investigated by culture-dependent methods. From the 16S rDNA and ITS sequence analyses of 68 epiphytic isolates, 5 bacterial species and 19 fungal species were identified. Aureobasidium pullulans and Rhodotorula glutinis were the dominant fungal species, while Enterococcus mundtii (Firmicutes) and Frigoribacterium faeni (Actinobacteria) were the most represented species among bacterial isolates. Enrichment cultures of fresh apricot puree, followed by fermentation trials in beer wort and beer wort added with apricot puree, allowed the selection of four isolates of Pichia kudriavzevii, Hanseniaspora uvarum, H. pseudoguilliermondii, and H. clermontiae able to dominate over the Bisucciu native microbiota and to produce from 0.57% to 0.74% (vol/vol) of ethanol. HS-SPME-GC/MS analysis highlighted a significant increase in the ester and alcohol fractions as well as a reduction in terpenes after fermentation with the selected yeasts. Results obtained suggest that the yeast isolates may contribute to the definition of the taste and flavor of beers when used in mixed fermentations with Saccharomyces.

Fruits of their labour: biotransformation reactions of yeasts during brewery fermentation

Abstract

There is a growing appreciation for the role that yeast play in biotransformation of flavour compounds during beverage fermentations. This is particularly the case for brewing due to the continued popularity of aromatic beers produced via the dry-hopping process. Here, we review the current literature pertaining to biotransformation reactions mediated by fermentative yeasts. These reactions are diverse and include the liberation of thiols from cysteine or glutathione-bound adducts, as well as the release of glycosidically bound terpene alcohols. These changes serve generally to increase the fruit and floral aromas in beverages. This is particularly the case for the thiol compounds released via yeast β-lyase activity due to their low flavour thresholds. The role of yeast β-glucosidases in increasing terpene alcohols is less clear, at least with respect to fermentation of brewer’s wort. Yeast acetyl transferase and acetate esterase also have an impact on the quality and perceptibility of flavour compounds. Isomerization and reduction reactions, e.g. the conversion of geraniol (rose) to β-citronellol (citrus), also have potential to alter significantly flavour profiles. A greater understanding of biotransformation reactions is expected to not only facilitate greater control of beverage flavour profiles, but also to allow for more efficient exploitation of raw materials and thereby greater process sustainability.

Key points

• Yeast can alter and boost grape- and hop-derived flavour compounds in wine and beer

• β-lyase activity can release fruit-flavoured thiols with low flavour thresholds

• Floral and citrus-flavoured terpene alcohols can be released or interconverted

Production of volatiles relation to bread aroma in flour-based fermentation with yeast

The aim of this study is to produce a bread aroma mixture in flour-based fermentation that can potentially be added in bread dough forming after selection of yeast strains and optimization of the fermentation conditions. S. cerevisiae PFC121 produced bread aroma compounds in higher amounts compared to other 20 strains. Also, this strain provided a more balanced volatiles in bread samples that gained consumer appreciation. When the PLS analysis were evaluated, 3-methyl-1-butanol, 2-phenylethyl alcohol, nonanal, and benzaldehyde were closely related with the whole wheat flour. Conversely, 2-methyl-1-propyl acetate, and 2-methyl-1-propanol were observed to be correlated with the fermentation temperature. PCA showed that 20 °C fermentation temperature was effective on the accumulation of benzaldehyde and nonanal. Extending the fermentation time increased alcohol and ester accumulation. In conclusion, S. cerevisiae PFC121 is a potential strain to produce bread related volatiles at the fermentation conditions that are wheat flour, 30 °C, 6 pH and 48-h.

Biotransformation of Hops-Derived Compounds in Beer – A Review

Besides providing bitterness to beer, hops also impart a whole range of aromas, such as herbal, spice, floral, citrus, fruity and pine to this beverage. Although hops are usually added in relatively small amounts, they have a significant impact on the sensory characteristics of the product. Raw hop aroma significantly differs from the aroma resulting from its addition to the beer. The final aroma of the beer arises from substances in the malt, hops, other additives, and yeast metabolism. The biochemical transformation of hop compounds by yeast has become more and more popular in recent years. Knowledge of this process may allow more precise control over the final sensory characteristics of the beverage. The article describes the chemical composition of hops and discusses the influence of the hopping regime on the concentration of volatile compounds in the finished product. Moreover, the article describes the biotransformation of hop-derived compounds by traditionally used Saccharomyces cerevisiae yeast, as well as less commonly used non-Saccharomyces yeast. The paper outlines the current state of knowledge on biotransformation of hop-derived hydrocarbons, terpenoids, esters, sulfur compounds and glycosidically bound aroma precursors.

The Impact of Dry Yeast Rehydrated in Different Plasma Treated Waters (PTWs) on Fermentation Process and Quality of Beer

Yeast plays a key role in the production of alcoholic beverages. Effective fermentation requires appropriate conditions to ensure the production of high-quality beer. The paper discusses the effect of dry brewing yeast (Saccharomyces cerevisiae and Saccharomyces pastorianus) after rehydration with water exposed to low-temperature, low-pressure glow plasma (PTW) in the atmosphere of air (PTWAir) and nitrogen (PTWN) in the course of the fermentation process, the formation of volatile compounds and other quality parameters of the finished beer. The obtained results show that the lager yeast strain initiated the process of fermentation faster after rehydration in the presence of PTWAir compared to all of the other treatments. It was observed that PTWAir significantly changed the composition of volatile compounds in the finished beer, especially by increasing the number of terpenes, which are compounds that positively shape the aroma of beer. In the case of PTWN samples, lower alcohol content, real extract, apparent extract and amount of biomass were observed in all analyzed strains.

Characteristics of New England India Pale Ale Beer Produced with the Use of Norwegian KVEIK Yeast

The aim of this research was to determine the potential of four unconventional Norwegian yeasts of the KVEIK type to produce NEIPA beer. The influence of yeast strains on fermentation process, physicochemical properties, antioxidant potential, volatile compounds, and sensory properties was investigated. The KVEIK-fermented beer did not differ in terms of physicochemical parameters from the beer produced with the commercial variants of US-05 yeast. The yeast strain influenced the sensory quality (taste and aroma) of the beers, with KVEIK-fermented beer rating significantly higher. The antioxidant activity of the tested beers also significantly depended on the yeast strain applied. The beers fermented with KVEIK had a significantly higher antioxidant potential (ABTS^•+) than those fermented with US-05. The strongest antioxidant activity was found in the beer brewed with the Lida KVEIK yeast. The use of KVEIK to produce NEIPA beer allowed enrichment of the finished products with volatile compounds isobutanol, 2-pentanol, 3-methylobutanol, ethyl octanoate, and ethyl decanoate.

Brewing of craft beer enriched with freeze-dried cape gooseberry: a promising source of antioxidants

Abstract The craft beer segment has been driving the beverage market due to the many different formulation possibilities. Among craft beers, fruity beers provide the consumer with flavors previously unknown. In this sense, cape gooseberry is a tropical fruit known for its unique flavor, whose production is seasonal, which makes it difficult to use throughout the year. One possibility of incorporating cape gooseberry into fruity beers is to subject the fruit to freeze-drying, ensuring a constant stock of pulp. The present study aimed to produce a craft beer added with freeze-dried cape gooseberry, to add mineral compounds, phenolic compounds, and antioxidant activity to the final beverage. Three beer formulations with different concentrations of freeze-dried cape gooseberry (20, 40, and 60 g/L) were produced and characterized. The results showed that the addition of the fruit directly influenced the physicochemical parameters pH, Total Titratable Acidity (TTA), Total Soluble Solids (TSS), alcoholic concentration, color, bitterness, real extract, primitive extract, and turbidity. In addition, the beers with freeze-dried cape gooseberry showed an increase in the content of some minerals, total phenolic compounds, and antioxidant activity. Thus, the addition of cape gooseberry is a good option to improve the functional characteristics of the beer, providing a differentiated product.

The Potential of Traditional Norwegian KVEIK Yeast for Brewing Novel Beer on the Example of Foreign Extra Stout

The development of craft brewing has spurred huge interest in unusual and traditional technologies and ingredients allowing the production of beers that would fulfil consumers' growing demands. In this study, we evaluated the brewing performance of traditional Norwegian KVEIK yeast during the production of Foreign Extra Stout beer. The content of alcohol of the KVEIK-fermented beer was 5.11-5.58% v/v, the extract content was 5.05-6.66% w/w, and the pH value was 4.53-4.83. The KVEIK yeast was able to completely consume maltose and maltotriose. The mean concentration of glycerol in KVEIK-fermented beers was higher than in the control sample (1.51 g/L vs. 1.12 g/L, respectively). The use of KVEIK-type yeast can offer a viable method for increasing the concentration of phenolic compounds in beer and for boosting its antioxidative potential. The beers produced with KVEIK-type yeast had a total phenol content of 446.9-598.7 mg GAE/L, exhibited antioxidative potential of 0.63-1.08 mM TE/L in the DPPH^• assay and 3.85-5.16 mM TE/L in the ABTS^•+ assay, and showed a ferric ion reducing capacity (FRAP) of 3.54-4.14 mM TE/L. The KVEIK-fermented bears contained various levels of volatile compounds (lower or higher depending on the yeast strain) and especially of higher alcohols, such as 3-metylobutanol, 2-metylobutanol, and 1-propanol, or ethyl esters, such as ethyl acetate or decanoate, compared to the control beers. In addition, they featured a richer fruity aroma (apricot, dried fruit, apples) than the control beers fermented with a commercial US-05 strain.

Efficient breeding of industrial brewing yeast strains using CRISPR/Cas9-aided mating-type switching

Yeast breeding is a powerful tool for developing and improving brewing yeast in a number of industry-relevant respects. However, breeding of industrial brewing yeast can be challenging, as strains are typically sterile and have large complex genomes. To facilitate breeding, we used the CRISPR/Cas9 system to generate double-stranded breaks in the MAT locus, generating transformants with a single specified mating type. The single mating type remained stable even after loss of the Cas9 plasmid, despite the strains being homothallic, and these strains could be readily mated with other brewing yeast transformants of opposite mating type. As a proof of concept, we applied this technology to generate yeast hybrids with an aim to increase β-lyase activity for fermentation of beer with enhanced hop flavour. First, a genetic and phenotypic pre-screening of 38 strains was carried out in order to identify potential parent strains with high β-lyase activity. Mating-competent transformants of eight parent strains were generated, and these were used to generate over 60 hybrids that were screened for β-lyase activity. Selected phenolic off-flavour positive (POF +) hybrids were further sporulated to generate meiotic segregants with high β-lyase activity, efficient wort fermentation, and lack of POF, all traits that are desirable in strains for the fermentation of modern hop-forward beers. Our study demonstrates the power of combining the CRISPR/Cas9 system with classic yeast breeding to facilitate development and diversification of brewing yeast. KEY POINTS: • CRISPR/Cas9-based mating-type switching was applied to industrial yeast strains. • Transformed strains could be readily mated to form intraspecific hybrids. • Hybrids exhibited heterosis for a number of brewing-relevant traits.

Impact of Oral Microbiota on Flavor Perception: From Food Processing to In-Mouth Metabolization

Flavor perception during food intake is one of the main drivers of food acceptability and consumption. Recent studies have pointed to the oral microbiota as an important factor modulating flavor perception. This review introduces general characteristics of the oral microbiota, factors potentially influencing its composition, as well as known relationships between oral microbiota and chemosensory perception. We also review diverse evidenced mechanisms enabling the modulation of chemosensory perception by the microbiota. They include modulation of the chemosensory receptors activation by microbial metabolites but also modification of receptors expression. Specific enzymatic reactions catalyzed by oral microorganisms generate fragrant molecules from aroma precursors in the mouth. Interestingly, these reactions also occur during the processing of fermented beverages, such as wine and beer. In this context, two groups of aroma precursors are presented and discussed, namely, glycoside conjugates and cysteine conjugates, which can generate aroma compounds both in fermented beverages and in the mouth. The two entailed families of enzymes, i.e., glycosidases and carbon-sulfur lyases, appear to be promising targets to understand the complexity of flavor perception in the mouth as well as potential biotechnological tools for flavor enhancement or production of specific flavor compounds.

Identification of new ethanol-tolerant yeast strains with fermentation potential from central Patagonia

The quest for new wild yeasts has increasingly gained attention because of their potential ability to provide unique organoleptic characters to fermented beverages. In this sense, Patagonia offers a wide diversity of ethanol-tolerant yeasts and stands out as a bioprospecting alternative. This study characterized the genetic and phenotypic diversity of yeast isolates obtained from Central Chilean Patagonia and analyzed their fermentation potential under different fermentative conditions. We recovered 125 colonies from Nothofagus spp. bark samples belonging to five yeast species: Saccharomyces eubayanus, Saccharomyces uvarum, Lachancea cidri, Kregervanrija delftensis, and Hanseniaspora valbyensis. High-throughput microcultivation assays demonstrated the extensive phenotypic diversity among Patagonian isolates, where Saccharomyces spp and L. cidri isolates exhibited the most outstanding fitness scores across the conditions tested. Fermentation performance assays under wine, mead, and beer conditions demonstrated the specific potential of the different species for each particular beverage. Saccharomyces spp. were the only isolates able to ferment beer wort. Interestingly, we found that L. cidri is a novel candidate species to ferment wine and mead, exceeding the fermentation capacity of a commercial strain. Unlike commercial strains, we found that L. cidri does not require nutritional supplements for efficient mead fermentation. In addition, L. cidri produces succinic and acetic acids, providing a distinct profile to the final fermented product. This work demonstrates the importance of bioprospecting efforts in Patagonia to isolate novel wild yeast strains with extraordinary biotechnological potential for the fermentation industry.

Aromatic Higher Alcohols in Wine: Implication on Aroma and Palate Attributes during Chardonnay Aging

The higher alcohols 2-phenylethanol, tryptophol, and tyrosol are a group of yeast-derived compounds that have been shown to affect the aroma and flavour of fermented beverages. Five variants of the industrial wine strain AWRI796, previously isolated due to their elevated production of the 'rose-like aroma' compound 2-phenylethanol, were characterised during pilot-scale fermentation of a Chardonnay juice. We show that these variants not only increase the concentration of 2-phenylethanol but also modulate the formation of the higher alcohols tryptophol, tyrosol, and methionol, as well as other volatile sulfur compounds derived from methionine, highlighting the connections between yeast nitrogen and sulfur metabolism during fermentation. We also investigate the development of these compounds during wine storage, focusing on the sulfonation of tryptophol. Finally, the sensory properties of wines produced using these strains were quantified at two time points, unravelling differences produced by biologically modulating higher alcohols and the dynamic changes in wine flavour over aging.

Molecular Insights into the Contribution of Specialty Barley Malts to the Aroma of Bottom-Fermented Lager Beers

Specialty barley malts provide unique aroma characteristics to beer; however, the transfer of specialty malt odorants to beer has not yet been systematically studied. Therefore, three beers were brewed: (1) exclusively with kilned base barley malt, (2) with the addition of a caramel barley malt, and (3) with the addition of a roasted barley malt. Major odorants in the beers were identified by aroma extract dilution analysis followed by quantitation and calculation of odor activity values (OAVs). The caramel malt beer was characterized by outstandingly high OAVs for odorants such as (E)-β-damascenone, 2-acetyl-1-pyrroline, methionol, 2-ethyl-3,5-dimethylpyrazine, and 4-hydroxy-2,5-dimethylfuran-3(2H)-one, whereas the highest OAV for 2-methoxyphenol was obtained in the roasted malt beer. Quantifying odorants in the malts revealed that the direct transfer from malt to beer played only a minor role in the amount of malt odorants in the beers, suggesting a substantial formation from precursors and/or a release of encapsulated odorants during brewing.

Increased Varietal Aroma Diversity of Marselan Wine by Mixed Fermentation with Indigenous Non-Saccharomyces Yeasts

The common use of commercial yeasts usually leads to dull wine with similar aromas and tastes. Therefore, screening for novel indigenous yeasts to practice is a promising method. In this research, aroma discrepancies among six wine groups fermentated with indigenous yeasts were analyzed. Three Saccharomyces yeasts (FS36, HL12, YT28) and three matched non-Saccharomyces yeasts (FS31, HL9, YT2) were selected from typical Chinese vineyards. The basic oenological parameters, aroma compounds, and sensory evaluation were analyzed. The results showed that each indigenous Saccharomyces yeast had excellent fermentation capacity, and mixed-strain fermentation groups produced more glycerol, contributing to sweeter and rounder taste. The results from GC-MS, principal components analysis (PCA), and sensory evaluation highlighted that the HL mixed group kept the most content of Marselan varietal flavors such as calamenene and β-damascone hereby ameliorated the whole aroma quality. Our study also implied that the indigenous yeast from the same region as the grape variety seems more conducive to preserve the natural variety characteristics of grapes.

Application of white grape pomace in the brewing technology and its impact on the concentration of esters and alcohols, physicochemical parameteres and antioxidative properties of the beer

Main by-product of white wine production is white grape pomace (WGP). It has attracted attention of food scientists, because it possesses high concentration of nutrients and bioactive substances. In this study, WGP was added to the beer after primary fermentation in two different concentrations (10% w/w and 20% w/w) and two different pretreatments (pasteurised and unpasteurised) to determine, whether the most abundant waste from white wine industry could be used to modify the volatilome and phenolic content of the beer. The addition of white grape pomace increased the concentration of phenolic compounds in all of the tested beers (from 321.584 mg gallic acid equivalent (GAE)/dm³ to 501.459 mg GAE/dm³). Antioxidant activity of the beers with addition of WGP (tested with the ABTS^+•, DPPH^• and FRAP assays) also increased. The composition of volatiles in beers changed as WGP was added. The most significant difference was in the concentration of acetaldehyde - beers with WGP added had 4-7 times lower acetaldehyde content (17.425-31.425 mg/dm³) than the control sample (134.050 mg/dm³).

Packing a punch: understanding how flavours are produced in lager fermentations

Beer is one of the most popular beverages in the world and it has an irreplaceable place in culture. Although invented later than ale, lager beers dominate the current market. Many factors relating to the appearance (colour, clarity and foam stability) and sensory characters (flavour, taste and aroma) of beer, and other psychological determinants affect consumers' perception of the product and defines its drinkability. This review takes a wholistic approach to scrutinise flavour generation in the brewing process, focusing particularly on the contribution of the raw ingredients and the yeasts to the final flavour profiles of lager beers. In addition, we examine current developments to improve lager beer flavour profiles for the modern consumers.

Assessment of the Suitability of Aromatic and High-Bitter Hop Varieties (Humulus lupulus L.) for Beer Production in the Conditions of the Małopolska Vistula Gorge Region

The aim of the study was to assess the yield of cones and the quality of six hop varieties (“Iunga”, “Lubelski”, “Sybilla”, “Magnum”, “Lomik”, “Marynka”) in terms of their suitability for beer production, under the conditions of the Małopolska Vistula Gorge Region (21°53′ E; 51°16′ N) (2015–2017). The scope of the research included the determination of the yield of cones and their physicochemical properties, as well as determination of the contents of hop resins and essential oils. In bitter varieties, the ratio of alpha-acids to beta-acids was stable, while, in aromatic varieties, it was variable. In the essential oils of the studied hop varieties, compounds with myrcene and α-humulene were identified and dominated the profiles. “Iunga”, “Sybilla”, “Lubelski”, and “Lomik” were rich in monoterpene hydrocarbons, mainly myrcene, while there was a bit more α-humulene in the “Marynka” variety. “Magnum” was characterized by an even distribution of monoterpenes and sesquiterpenes. The “Magnum variety turned out the most useful for the brewing industry in this region. The Małopolska Vistula Gorge Region is a region where hops not only achieve a high yield of cones, but also good-quality. The bitterness and aroma content of the hops in this region is high.

Impact of Dry Hopping on Beer Flavor Stability

To investigate the chemical and sensorial impact of dry hopping time on typical pale ale, a standardized beer was produced and separated into ten vessels. Nine vessels were dry hopped, and one vessel remained un-hopped as a control. Impact of dry hopping contact time was investigated over 96 h. Polyphenols and iso-α-acid t/c ratio were analyzed in both Young and Aged beer samples. Total polyphenol content generally increased in both young and aged treatments compared to controls. Analysis of the t/c ratio suggests that both Young and Aged beers were chemically preserved to some degree after approximately 12 h at the given dry hopping rate regardless of age. Within the Aged beer trials, 96 h of dry hop contact yielded a significant increase in t/c ratio compared to all other Aged trials. This suggests that a 4-day dry hop regime may yield additional oxidative protection of iso-α-acids in beers stored unrefrigerated for 30 days. Descriptive analysis was also performed with an 8-person, trained panel; however, beers were sensorially distinguished by their aging time as opposed to their dry hopping time.

Biosyntheses of geranic acid and citronellic acid from monoterpene alcohols by Saccharomyces cerevisiae

Geraniol is one of the important aromatic ingredients in alcoholic beverages. Bioconversions of geraniol to other terpenoids and genes involved in the oxidation of geraniol were investigated. Geranic acid and citronellic acid were detected in yeast culture, where geraniol or nerol was added. Addition of citral, a mixture of geranial and neral, resulted in the production of geranic acid and citronellic acid, whereas the addition of citral or citronellal resulted in the production of citronellic acid, suggesting that citronellic acid might be produced through the conversion of citral to citronellal followed by the oxidation of citronellal. Consumption of geraniol and production of geranic acid, citronellic acid, and citronellol were affected in adh1Δ, adh3Δ, adh4Δ, and sfa1Δ yeast strains, which possess single deletion of a gene encoding alcohol dehydrogenase. This is the first report of the bioconversion of monoterpene alcohols, geraniol and nerol, to geranic acid and citronellic acid in yeast culture.

Role of Yeasts in the Brewing Process: Tradition and Innovation

Nowadays, in the beer sector, there is a wide range of products, which differ for the technologies adopted, raw materials used, and microorganisms involved in the fermentation processes. The quality of beer is directly related to the fermentation activity of yeasts that, in addition to the production of alcohol, synthesize various compounds that contribute to the definition of the compositional and organoleptic characteristics. The microbrewing phenomenon (craft revolution) and the growing demand for innovative and specialty beers has stimulated researchers and brewers to select new yeast strains possessing particular technological and metabolic characteristics. Up until a few years ago, the selection of starter yeasts used in brewing was exclusively carried out on strains belonging to the genus Saccharomyces. However, some non-Saccharomyces yeasts have a specific enzymatic activity that can help to typify the taste and beer aroma. These yeasts, used as a single or mixed starter with Saccharomyces strains, represent a new biotechnological resource to produce beers with particular properties. This review describes the role of Saccharomyces and non-Saccharomyces yeasts in brewing, and some future biotechnological perspectives.

Exploring the Lipids Involved in the Formation of Characteristic Lactones in Japanese Black Cattle

The meat from Japanese Black cattle (Japanese Wagyu) is finely marbled and exhibits a rich and sweet aroma known as Wagyu beef aroma. To clarify the key metabolites involved in the aroma, we analyzed the correlation between lactone and lipid composition in Japanese Black cattle. Using gas chromatography-olfactometry, we identified 39 characteristic odorants of the intermuscular fat. Seven characteristic lactones considered to be involved in Wagyu beef aroma were quantified and compared in the marbled area and intermuscular fat using a stable isotope dilution assay. Among them, γ-hexalactone was the only lactone whose level was significantly higher in the marbled area. To explore the lipid species involved in lactone formation, we analyzed samples with different aroma characteristics. Liquid chromatography-mass spectrometry revealed eight lipid classes and showed significant differences in triacylglycerides (TAGs). To determine the molecular species of TAGs, we performed high-performance liquid chromatography analysis and identified 14 TAG species. However, these analyses showed that seven lactones had a low correlation with the TAGs. However, γ-hexalactone showed a positive correlation with linoleic acid. This study suggests that lipid composition affects the characteristic lactone profile involved in the Wagyu beef aroma.