Biotransformations of hop-derived aroma compounds by Saccharomyces cerevisiae upon fermentation

Effect of Coriander Seed Addition at Different Stages of Brewing on Selected Parameters of Low-Alcohol Wheat Beers

In recent years, there has been a significant decline in interest in high-alcohol beers, while interest in low- and non-alcohol beers is growing. The aim of this study was to investigate the influence of the addition of coriander seeds at various stages of the production of low-alcohol wheat beer (mashing, boiling, and fermentation). The presented article uses biological methods to produce low-alcohol beer. For this purpose, first, the mashing process was modified (breaking 44 °C for 20 min, followed by 75 °C for 60 min). The chemical composition and aroma components of the obtained beers were determined using various chromatographic methods (HPLC, GC-MS, and GC-O). Differences were found between the aroma components depending on the stage of production at which the coriander seeds were added. Beers with the addition of coriander seeds at the fermentation stage had the highest terpene content (linalool, camphor, trans-linalool oxide, and γ-terpinene) and boiling (myrcene, limonene, citronellol, and geraniol). The least desirable process is the addition of coriander seeds at the mashing stage due to the lowest content of volatile compounds. Additionally, beers with the addition of coriander seeds for fermentation were characterized by a higher content of antioxidant compounds. This proves that the addition of coriander seeds during beer production could improve the fermentation process and modify the quality of the obtaining beer.

The Impact of Hop Freshness on Kettle-Hopped Beers

Hops are an indispensable ingredient in beer, and the differences in their chemical composition impart the various tastes and aromas associated with different beers. However, during storage, hops undergo changes in their chemical composition. Here, the changes in aroma and bitterness of kettle-hopped beers were evaluated in an experiment conducted on three different hop varieties (Aurora, Celeia and Styrian Wolf) with five different hop storage index (HSI) values (0.3-0.7). Hops were added to boiling wort for 5, 45 and 90 min. Alpha-acids, iso-alpha-acids, humulinones, bitterness units and hop aroma compounds in the samples were chemically analysed. All samples also underwent sensorial analysis. The old hops were not problematic in terms of bitterness or early hopping time. However, later additions of old hops reduced the quality and intensity of the hop aroma. The limit value for use without negative consequences for kettle hopping was set at HSI 0.5 for Aurora and Celeia and HSI 0.6 for Styrian Wolf.

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.

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.

Biotransformations Performed by Yeasts on Aromatic Compounds Provided by Hop—A Review

The biodiversity of some Saccharomyces (S.) strains for fermentative activity and metabolic capacities is an important research area in brewing technology. Yeast metabolism can render simple beers very elaborate. In this review, we examine much research addressed to the study of how different yeast strains can influence aroma by chemically interacting with specific aromatic compounds (mainly terpenes) from the hop. These reactions are commonly referred to as biotransformations. Exploiting biotransformations to increase the product’s aroma and use less hop goes exactly in the direction of higher sustainability of the brewing process, as the hop generally represents the highest part of the raw materials cost, and its reduction allows to diminish its environmental impact.

Yeast Strain Influences the Hop-Derived Sensory Properties and Volatile Composition of Beer

The perception of hop-derived flavour in beer is not well understood, particularly regarding the effect that different yeast strains and fermentation parameters have on perceived hop aroma and the mechanisms responsible for these changes. To evaluate the influence of yeast strain on the sensory properties and volatile composition of beer, a standard wort, late-hopped with New Zealand Motueka hops (5 g·L^-1), was fermented with one of twelve yeast strains under constant conditions (temperature and yeast inoculation rate). The bottled beers were evaluated using a free sorting sensory methodology, and their volatile organic compounds (VOC) were assessed using gas chromatography mass spectrometry (GC/MS) with headspace solid-phase microextraction (SPME) sampling. Beer fermented with SafLager W-34/70 yeast was associated with a hoppy flavour attribute, whereas WY1272 and OTA79 beers were sulfury, and WY1272 was also metallic. WB06 and WLP730 beers were perceived to be spicy, with WB06 beer also perceived as estery, whereas VIN13 beer was sour, and the WLP001 beer was astringent. Beers fermented using the twelve yeast strains had clearly distinct VOC profiles. Beer made with WLP730, OTA29, SPH, and WB06 yeasts had the highest 4-vinylguaiacol levels, which contributed to their spicy attribute. Beer made with W3470 had high levels of nerol, geraniol, and citronellol, which supported its sensory characterisation as being 'hoppy'. This research has illustrated the important role that yeast strain has on modulating hop flavour in beer.

Tracking Wheat Variety and Origin by the Shape Analysis of the Volatiles Fingerprint of Wheat Kernels and Wheat Beers

The Volatile Organic Compounds (VOCs) of common wheat of different origin (variety and altitude of cultivation) and craft wheat beers produced by using the wheat themselves were analyzed by SPME GC-MS. The VOCs of wheat kernels and wheat beers were compared, and 14 common flavor-active compounds were identified. Principal component analysis was used to describe changes in the profile of common volatiles induced by beer processing. A unifying approach by Generalized Procrustes analysis (GPA), which considers the overall characteristics of the datasets, permitted linking the VOCs of wheat to those of beers and to define a common flavor pattern. Despite the beer processing deeply affecting the overall volatilome profile, a consensus map permitted to clearly classify the VOCs profile of five out of six samples. This work revealed that differences in wheat VOCs induced by wheat variety and cultivation site were reflected in different beer aromatic profiles, highlighting the importance of origin on the wheat and beers’ flavor. This unifying approach to flavor analysis by GPA could be of help in sight of a certification of origin, since it may contribute not only to the definition of wheat origin but also of the “terroir” of wheat beer thereof.

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

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 Occurrence of Glycosylated Aroma Precursors in Vitis vinifera Fruit and Humulus lupulus Hop Cones and Their Roles in Wine and Beer Volatile Aroma Production

Volatile aroma compounds found in grapes and hops may be present as both free volatiles and bound glycosides. Glycosides found in the raw materials are transferred to their respective fermented beverages during production where the odorless compounds may act as a reservoir of free volatiles that may be perceived by the consumer if hydrolyzed. A review of the literature on grape and wine glycosides and the emerging literature for glycosides in hops is presented in order to demonstrate the depth of history in grape glycoside research and may help direct new research on hop glycosides. Focus is brought to the presence of glycosides in the raw materials, the effect that winemaking and brewing have on glycoside levels, and current methods for the analysis of glycosidically linked aroma compounds.

Bottle Conditioning: Technology and Mechanisms Applied in Refermented Beers

Bottle conditioning refers to a method of adding fermenting wort or yeast suspension in sugar solution into beer in its final package. Additionally denoted as bottle refermentation, this technique has been originally developed to assure beer carbonation, and has further significance related to formation of distinctive sensory attributes and enhancement of sensory stability, which are the phenomena associated with ongoing yeast metabolic activities in the final package. This review covers historical development of the method, describes metabolic pathways applied during refermentation, and explains practical aspects of the refermentation process management. Furthermore, an overview of the traditional and novel approaches of bottle conditioning with mixed yeast bacterial cultures and its impact on the properties of final beer is provided.

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

Aroma compounds provide attractiveness and variety to alcoholic beverages. We discuss the molecular biology of a major subset of beer aroma volatiles, fruity and floral compounds, originating from raw materials (malt and hops), or formed by yeast during fermentation. We introduce aroma perception, describe the most aroma-active, fruity and floral compounds in fruits and their presence and origin in beer. They are classified into categories based on their functional groups and biosynthesis pathways: (1) higher alcohols and esters, (2) polyfunctional thiols, (3) lactones and furanones, and (4) terpenoids. Yeast and hops are the main sources of fruity and flowery aroma compounds in beer. For yeast, the focus is on higher alcohols and esters, and particularly the complex regulation of the alcohol acetyl transferase ATF1 gene. We discuss the release of polyfunctional thiols and monoterpenoids from cysteine- and glutathione-S-conjugated compounds and glucosides, respectively, the primary biological functions of the yeast enzymes involved, their mode of action and mechanisms of regulation that control aroma compound production. Furthermore, we discuss biochemistry and genetics of terpenoid production and formation of non-volatile precursors in Humulus lupulus (hops). Insight in these pathways provides a toolbox for creating innovative products with a diversity of pleasant aromas.

Investigations on the Impact of the Special Flavor Hop Variety Huell Melon on the Odor-Active Compounds in Late Hopped and Dry Hopped Beers

Bottom-fermented and top-fermented beers, both either late or dry hopped with Huell Melon hops, and respective reference beers without late or dry hopping were subjected to a comparative odorant screening by aroma extract dilution analyses. On the basis of differences in the FD factors, 14 odorants were identified as hop-derived. Among them were ethyl 2-methylpropanoate, methyl 2-methylbutanoate, ethyl 2-methylbutanoate, propyl 2-methylbutanoate, myrcene, linalool, and geraniol. Differences between late hopped, dry hopped, and reference beers were substantiated by quantitation. Results showed minimal transfer of myrcene from hops into beer. Moderate transfer was observed for propyl 2-methylbutanoate, geraniol, and linalool. Process-induced changes of ethyl 2-methylpropanoate, ethyl 2-methylbutanoate, and methyl 2-methylbutanoate were beyond a direct transfer from hops into beer, suggesting a formation from the corresponding hop-derived carboxylic acids by yeast. Spiking experiments revealed that linalool and propyl 2-methylbutanoate contributed particularly to the characteristic aroma of beers flavored with Huell Melon hops.

Evaluation of PTR-ToF-MS as a tool to track the behavior of hop-derived compounds during the fermentation of beer

Hop-derived volatile organic compounds (VOCs) play an important role in the flavor and aroma of beer, despite making up a small percentage of the overall profile. To understand the changes happening during fermentation, proton transfer reaction-time of flight-mass spectrometry (PTR-ToF-MS) was applied for the first time in brewing science to directly measure the changes in hop-derived VOCs during the fermentation of four different worts containing one of two aroma hops in combination with one of two yeast biotypes. PTR-ToF-MS successfully detected and tracked mass-to-charge ratios (m/z) arising from interactions between the different yeast strains and the hop cultivars. Differences were observed in the dynamic VOC profiles between different beer treatments for m/z such as m/z 145.121 (ethyl hexanoate) and m/z 173.153 (isoamyl isovalerate or ethyl octanoate). The ability to monitor changes in VOCs during fermentation provides valuable information on the priority of production and transformation reactions by yeast.

Characterization of the recombinant Brettanomyces anomalus β-glucosidase and its potential for bioflavouring

AIM

Plant materials used in the food industry contain up to five times more aromas bound to glucose (glucosides) than free, unbound aromas, making these bound aromas an unused flavouring potential. The aim of this study was to identify and purify a novel β-glucosidase from Brettanomyces yeasts that are capable of releasing bound aromas present in various food products.

METHODS AND RESULTS

We screened 428 different yeast strains for β-glucosidase activity and are the first to sequence the whole genome of two Brettanomyces yeasts (Brettanomyces anomalus and Brettanomyces bruxellensis) with exceptionally high β-glucosidase activity. Heterologous expression and purification of the identified B. anomalus β-glucosidase showed that it has an optimal activity at a higher pH (5·75) and lower temperature (37°C) than commercial β-glucosidases. Adding this B. anomalus β-glucosidase to cherry beers and forest fruit milks resulted in increased amounts of benzyl alcohol, eugenol, linalool and methyl salicylate compared to Aspergillus niger and Almond glucosidase.

CONCLUSIONS

The newly identified B. anomalus β-glucosidase offers new possibilities for food bioflavouring.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study is the first to sequence the B. anomalus genome and to identify the β-glucosidase-encoding genes of two Brettanomyces species, and reports a new bioflavouring enzyme.

The Bitter Chemodiversity of Hops (Humulus lupulus L.)

To map the chemodiversity of key bitter compounds in hops, a total of 75 different samples collected from the global hop market were analyzed for 117 key bitter tastants by means of a multiparametric HPLC-MS/MSMRM method. Among the compounds detected, 2'',3''-epoxyxanthohumol was detected for the first time in hops and iso¬xantho¬humol M was identified as a marker compound for varieties grown in Germany. Hop ageing experiments in the absence and presence of air oxygen, respectively, were conducted to address the stability of hop-derived compounds during long-term storage.

Sensomics analysis of key bitter compounds in the hard resin of hops (Humulus lupulus L.) and their contribution to the bitter profile of Pilsner-type beer

Recent brewing trials indicated the occurrence of valuable bitter compounds in the hard resin fraction of hop. Aiming at the discovery of these compounds, hop's ε-resin was separated by means of a sensory guided fractionation approach and the key taste molecules were identified by means of UV/vis, LC-TOF-MS, and 1D/2D-NMR studies as well as synthetic experiments. Besides a series of literature known xanthohumol derivatives, multifidol glucosides, flavon-3-on glycosides, and p-coumaric acid esters, a total of 11 bitter tastants are reported for the first time, namely, 1",2"-dihydroxanthohumol F, 4'-hydroxytunicatachalcone, isoxantholupon, 1-methoxy-4-prenylphloroglucinol, dihydrocyclohumulohydrochinone, xanthohumols M, N, and P, and isoxanthohumols M, N, and P, respectively. Human sensory analysis revealed low bitter recognition threshold concentrations ranging from 5 (co-multifidol glucopyranoside) to 198 μmol/L (trans-p-coumaric acid ethyl ester) depending on their chemical structure. For the first time, LC-MS/MS quantitation of these taste compounds in Pilsner-type beer, followed by taste re-engineering experiments, revealed the additive contribution of iso-α-acids and the identified hard resin components to be truly necessary and sufficient for constructing the authentic bitter percept of beer. Finally, brewing trails using the ε-resin as the only hop source impressively demonstrated the possibility to produce beverages strongly enriched with prenylated hop flavonoids.

Use of hydrodistillation and headspace solid-phase microextraction to characterize the volatile composition of different hop cultivars

BACKGROUND

Hop cones, the immature inflorescences of the female plant of Humulus lupulus L., have been used for centuries to improve the flavor of beer and can be also used for a great variety of other products. Four samples of hop, belonging to three different cultivars (Nugget, Saaz and Perle), were studied in the present work. Headspace solid-phase microextraction and hydrodistillation techniques were used to obtain the volatile profiles of the samples.

RESULTS

Independent of the technique employed, over 40 volatile compounds were detected in the hop pellet samples (esters, monoterpenes, monoterpenoids, sesquiterpenes and sesquiterpenoids). Sesquiterpenes and sesquiterpenoids represented the majority of the total aromatic compounds. The main compounds for all cultivars were myrcene, β-caryophyllene and humulene, but the presence of high amounts of β-farnesene in Saaz cultivar was highlighted.

CONCLUSION

Both techniques were suitable for studying qualitatively the volatile composition of hop pellets, but some differences were shown when studying the proportion of the main constituents of the volatile profiles. Understanding these differences may help researchers design future studies to advise the industry how to exploit the potential of each hop cultivar.

Different beers with different hops. Relevant compounds for their aroma characteristics

Hop-derived aroma characteristics in beer are very important for the quality of beer. This study compared the differences of hop aroma characteristics and the compounds contained in beer by changing the variety of hops applying the idea of "food metabolomics" on the GC×GC/TOF-MS analysis data, to clarify which aroma compounds contribute to the differences of hop aroma profiles indicated by sensory descriptors. As a result, by focusing only on hop-derived compounds, 67 compounds were strongly correlated with one or more of the sensory descriptors. Furthermore, the odor descriptions of each key compound corresponded well to each sensory descriptor. Thus, these compounds are likely to be the key compounds explaining the differences of hop aroma characteristics in beer. This study led to the suggestion that understanding the relationship between the comprehensive nontarget analysis by GC×GC-TOF/MS and organoleptic evaluation using PCA is effective in estimating the key compounds.