Hop Aroma Research Articles

The Comparison and Brewing Value of Saaz Hop Pedigree

The well-known hop variety, Saaz, which gives the Pilsner lager beer its characteristic hop aroma, may be threatened by climate change in the future. Therefore, new Saaz-related hop varieties, including Saaz Late, Saaz Brilliant, Saaz Comfort, and Saaz Shine, were recently bred. A comparison study was carried out to evaluate whether these varieties are acceptable for traditional lagers. For this purpose, sensorial and chemical analyses of hops and related beers, namely, an analysis of hop resins and oils, were performed. Sensory profiles of Saaz varieties are very similar (fine, hoppy aroma; floral; herbal), except for Saaz Comfort, which has a slightly higher aroma intensity, and Saaz Shine, which has the most noticeable fruity scent, with traces of citrus. The chemical profiles are also very similar, with α-humulene, β-pinene, (E)-β-farnesene, β-caryophyllene, and myrcene being the most abundant. Decoction mashing and kettle hopping technology with bottom fermentation show that the compared varieties result in very similar lager beers with hoppy, floral, herbal, fruity, and spicy aromas. Typical hop oils include farnesol, linalool, methyl geranate, β-pinene, and limonene. The high concentration of farnesol in beer correlates with the concentrations of (E)-β-farnesene and farnesol in hops. New Saaz varieties are widely used to produce Pilsner lager without affecting the traditional sensory aroma of this widespread style. Varieties have a higher yield of approximately 25% and bitter acid concentrations of approximately 15%, with Saaz Comfort comprising approximately 100%. Furthermore, the concentration of hop oils is approximately 40% higher in Saaz Shine than a traditional Saaz variety. Moreover, Saaz Shine and Saaz Comfort have very good resistance to drought, which is an important property from a climate change perspective.

ANÁLISE DE ÓLEOS VOLÁTEIS DE LÚPULO (Humulus lupulus L.) CASCADE E CHINOOK CULTIVADOS SOB CLIMA TROPICAL NO ESTADO DE SÃO PAULO

ANALYSIS OF VOLATILE OILS FROM CASCADE AND CHINOOK HOPS (Humulus Lupulus L.) CULTIVATED UNDER TROPICAL CLIMATE IN THE STATE OF SÃO PAULO. Hop (Humulus lupulus L.) is a plant widely used as raw material in global beer production, valued for its aroma, flavor and bittering components. Despite Brazil’s third-place position in global beer production, the country still relies on imported hops. Thus, this study describes the chemical composition and volatile oil content of Cascade and Chinook hop cultivars grown in a tropical area in São Paulo state during 2020 and 2021, as well as imported commercial pellets. Hydrodistillation was employed to extract the oils, which were analyzed using GC-FID and GC-MS techniques. Approximately 40% of the cultivated hop plants exhibited volatile oil content within the expected range. Among the 55 identified compounds, β-myrcene, β-caryophyllene, and α-humulene were the major constituents, and several key compounds contributing to hop aroma were detected. Principal component analysis revealed distinct clustering patterns based on cultivar and harvest year. This study reports the first comparative analysis of hops harvested in different years and the volatile oil composition and content of Chinook hops cultivated in Brazil, making a significant contribution to the fields of agronomy and national beer market. These findings highlight Brazil’s potential to become a major hop producer by implementing proper management practices and suitable technologies.

Impartment of spicy, fruity and herbal aromas from the Czech hop varieties of Ceres, Pluto and Saturn to beer

The aim of the study is to evaluate the intensity and character of the beer aroma in selected hop varieties. In 2022 and 2023, new Czech Flavour hop varieties of Ceres, Pluto, and Saturn were registered. Ceres exhibits a mild citrusy and fruity hop aroma. Pluto has an intense fruity and herbal aroma, while Saturn has an intense fruity aroma with a milder citrus note. Differences in the intensity and character of the beer aroma were identified based on the hop variety used and the cold hopping dose. These varieties and their combinations were tested under cold hopping at 3 g/l and 6 g/l to assess the impartment of the aromas to beer. The combination of Pluto + Saturn shows the highest intensity of a spicy aroma, while Ceres exhibits the highest intensity of both the fruity and herbal aromas – all this at 6 g/l. The best character of the spicy aroma is observed with Ceres at 3 g/l. Ceres also demonstrates the best character of the fruity aroma, and Ceres + Pluto combination excels in the herbal aroma, both at the dose of 6 g/l. The popularity of beer is crucial, with the combination of Ceres + Pluto at 3 g/l proving to be the most popular. The results have practical applications in breweries producing bottom-fermented beers that utilize dry hopping. It is obvious which hop varieties or their combinations can be used to accentuate individual aroma profiles.

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.

Insight into the aroma quality of ‘Callista’ cultivar of hop (Humulus lupulus L.): impact of harvest timing, year, and location

Hops (Humulus lupulus L.) are essential ingredients in brewing, contributing to beer’s flavor, aroma, and stability. This study pioneers an in-depth analysis of the 'Callista' cultivar, aiming to unravel how harvest timing, annual variations, and cultivation location synergistically influence its molecular profile, sensory perception, and biochemistry. Leveraging high-performance liquid chromatography and gas chromatography-mass spectrometry-olfactometry, we identified significant year-to-year and location-based fluctuations in bitter acids—the quintessential aroma constituents in hops. Our comprehensive aroma profiling discerned 55 volatile compounds, marking the first-ever sensory detection of 2-butanone in hops, with its presence showing remarkable interannual variability. This study showed significant differences among the three years tested, whereas hops were perceived “fruitier” and more “citrusy” in 2021, even though the bitter acid and aroma analysis showed that 2022 sticks out due to extremely high lupulone values up to 10% dry cone weight and 78% β-myrcene in the oil fraction compared to 60% and 45% in 2020 and 2021, respectively. Molecular analysis of key enzymes involved in hop aroma biosynthesis revealed no significant associations with location, but a strong diurnal pattern for all genes. The results indicated that especially the hot temperatures of 2022 may have induced significant changes of cone quality, while 2021 was more interesting from the sensory evaluations, which may justify the usage of viticultural terms such as “vintage” for hop marketing. These findings contribute to a better understanding of the factors influencing hop aroma and quality.

Optimizing brewing beer production using Aspergillus oryzae solid-state fermentation of sorghum koji as an adjunct

ABSTRACT This study employed solid-state fermentation (SSF) to substitute 30% barley malt with Kinmen waxy sorghum and Australian non-waxy sorghum inoculated with Aspergillus oryzae for koji preparation in the production of sorghum beer. Optimal conditions for koji preparation were determined, and various beer formulations were developed based on Kinmen sorghum koji. The optimal soaking time for Kinmen waxy and Australian non-waxy sorghum was 2.5 h at room temperature with a water absorption rate of 35%. After steaming, Kinmen sorghum and Australian sorghum exhibited blowup rates of 75.33% and 85.67%, respectively. Five beer types were fermented for 12 days using different mashing methods. Glucose content ranged from 9.93 to 17.6 g/L on the first day, decreasing to 0.03 g/L by the third day. On the 12th day, the alcohol content peaked at 3.03–4.39%, with a pH range of 4.3–5.7. Aroma analysis identified higher alcohols, such as ethanol, 3-methyl-1-butanol, and 2-phenyl ethanol, as the main contributors, with 2-phenyl ethanol imparting a solid rose flavor and ethanol providing a hop aroma and mild taste. Given the global competitiveness of the beer industry, our research emphasizes the use of Kinmen sorghum-based malt, offering unique flavors and a rich aroma, presenting significant growth potential in the market.

Drought-tolerant hop genotypes – A promising solution to the problem of climate change for the hop industry?

Climate change can negatively influence hop yield and its quality. Cultivation areas limited by the prohibition of using water from small water sources are most at risk. In order to prevent these areas from completely disappearing in the future, planting hops with varieties or genotypes tolerant to drought could be a promising solution. Therefore, Czech hop breeding targets drought-tolerant genotypes with high crop yield and stability of quantitative and qualitative parameters which will also be well-usable in the Czech brewing industry. Twelve promising genotypes (5165 (Uran), 5194, 5304, 5348, 5398, 5432, 5461, 5464, 5465, 5646, 5669, and 5693) were selected after measurement of their physiological parameters and their basic chemical and sensorial properties were determined. Simultaneously, they were assessed from the point of view of brewing quality using sensory and chemical analysis using a brewing test. For this purpose, experimental beer using identical decoction single-hopped technology, where a hop aroma was highlighted using hopping in a whirlpool was prepared. The results show that three genotypes belong to the category of bitter varieties (5165, 5194, and 5304), whereas the other are genotypes exhibiting the character of aromatic varieties. From a grower’s point of view, genotypes 5165 (Uran), 5194, 5348, 5398, and 5461 show a very high yield. The overall impression of all beer samples is very good, bitterness is fine in most samples and hop aroma is mostly hoppy, herbal, woody, spicy, and in some cases also fruity (5304, 5461, 5465, 5646, and 5693).

Evaluation of Czech hop varieties (Humulus lupulus L.) in a dry area without irrigation

Since 2017, a field experiment has been conducted in a dry area with 11 Czech hop varieties. The highest yields were achieved by the Uran variety (2.83 t/ha) and Saaz Shine variety (2.76 t/ha), which also exhibited the lowest yield variability, at 11.17% (Saaz Shine) and 12.53% (Uran). The lowest hop yield was recorded by the Harmonie variety (1.17 t/ha), which also showed high yield variability (30.92%). The Bohemie variety had the highest yield variability of hops at 35.26%. While the Gaia (14.66% w/w) and Uran (13.53% w/w) varieties had the highest alpha acid content. Conversely, the Mimosa variety showed the lowest alpha acid content (1.56% w/w) and also the lowest alpha/beta acid ratio (0.29). The Rubín variety reached the highest alpha/beta acid ratio (3.00). The Uran variety exhibited the lowest variability in alpha (6.16%) and beta (6.28%) acid content. In contrast, the Harmonie variety had the highest variability in alpha (59.02%) and beta (38.18%) acid content. The Uran and Saaz Shine varieties are the most suitable for the dry area. Additionally, the Gaia and Saaz Brilliant varieties showed good performance parameters. The hop varieties Vital, Gaia, Saaz Brilliant, and Saaz Shine had the most intense hop aroma, while the Boomerang and Uran varieties had a high intensity of spicy aroma.

Effect of Extraction Time on the Yield, Chemical Composition, and Antibacterial Activity of Hop Essential Oil Against Lactic Acid Bacteria (Lactobacillus brevis and Lactobacillus casei) Beer Spoilage.

Hop essential oil (EO) generates interest for its antioxidant and antimicrobial properties, in addition to the volatile compounds that are responsible for the hop aroma in beer. Thus, the objective of this study was to evaluate the chemical composition, EO yield, and antibacterial activity of hop essential oil from hops of the Chinook variety against lactic acid bacteria (Lactobacillus brevis and Lactobacillus casei) at different times of extraction. EO extraction was performed by hydrodistillation at different times. By analyzing the chemical composition by gas chromatography and mass spectrometry, the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) were determined. The major compounds of hop EO were α-humulene, β-myrcene, and β-caryophyllene, and the extraction yields were 0.67, 0.78, and 0.85% mass of EO per mass of hops pelletized hops (m/m), for extractions of 90, 180, and 300min, respectively. The EO obtained in 90min was efficient against L. casei at 2.5mg/mL (MIC) and 5.0mg/mL (MBC), and the 300min one against L. brevis at 2.5mg/mL (MIC) and 25mg/mL (MBC). The antibacterial activity was affected by the chemical makeup of the oil, revealing that the hop EO extracted in 300min was the most efficient among the other extraction times.

Nitrogen and Sulfur Fertility Practices: Influences on Hop Chemistry, Aroma, and Nitrate Accumulation

Multiphasic studies were conducted to quantify how sulfur fertilization influences nitrate levels in hops, and how nitrogen and sulfur fertilizer dose jointly affect hop yield, brewing chemistry, and aroma of hops and beer. In an observational study of commercial lots of Simcoe® hops, a weak positive correlation was found between sulfur and nitrate concentrations. In field studies with Simcoe® in Washington, factorial combinations of representative low and high rates of nitrogen and sulfur fertilizer revealed that nitrate content of cones increased 13 to 22% with increasing nitrogen dose yet declined 8 to 8.7% with an increasing sulfur dose. Yield was unaffected by the lower dose of nitrogen when sulfur dose was high; effects on α-acids, total oil, and hop and beer aroma were not detected. Cysteine-3SH and cysteinylglycine-3SH were reduced 19% and 23%, in cones that received the higher sulfur dose in one year; other thiols and precursors were unaffected. In cultivar Willamette in Oregon, increasing sulfur dose over an 11-fold range by varying nitrogen fertilizer form from urea to ammonium sulfate had small to non-detectable effects on yield, α-acids, or nitrate concentrations. Hop aroma and brewing characteristics appear largely invariant to sulfur fertilization; increased sulfur fertilization may reduce hop nitrate levels modestly in certain situations.

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.

Predicting the essential oil composition in supercritical carbon dioxide extracts from hop pellets using mathematical modeling

Supercritical fluid extraction from hops (Humulus lupulus L.) can be used to extract essential oil for the flavoring of beer. With a special focus on the oil composition being linked to the hop aroma, the influence of pressure and temperature on the extraction kinetics of seven oil components (β-myrcene, α-humulene, β-caryophyllene, 2-methylbutyl isobutyrate, undecanone, linalool, and α-pinene) is analyzed and modeled in this article.Supercritical CO2 extraction from hop pellets was conducted at pressure-temperature combinations of 90/100/110 bar and 40/45/50 °C. The extract composition over time, analyzed by gas chromatography, was used for the parameterization of two existing mechanistic models: an internal-mass-transfer-control (IMTC), and a broken-and-intact-cells (BIC) model. The IMTC model was found to effectively describe most extraction kinetics and hence applied in this study. In contrast to previous studies, the IMTC model parameters were not only fitted to individual extraction curves from different experiments but also correlated to temperature and pressure as a further step towards model-based prediction. Using the parameterized model, the extract composition was predicted at 95 bar/48 °C, 105 bar/42 °C, and 105 bar/48 °C.Extraction yields were found to be higher at lower temperatures and higher pressures in general. The sensitivity towards pressure was observed to differ between components and to be particularly higher for β-myrcene compared with α-humulene. Changes of the essential oil composition with a variation in pressure and temperature were predicted correctly by the model with a mean relative deviation from experimental data of 11.7% (min. 1.2%, max. 36.2%).

The influence of Torulaspora delbrueckii on beer fermentation.

In this study, the effect of five different Torulaspora delbrueckii strains in combination with an ale type Saccharomyces cerevisiae on physical, chemical, microbiological, aroma composition, and sensory profiles of beer were examined. The ethyl alcohol content of produced beers ranged from 5.46% (v/v) to 5.93% (v/v), while the highest alcohol amount was obtained using a pure culture of S. cerevisiae. The major volatiles among beer aroma compounds was acetaldehyde, n-propanol, 3-methyl-butanol, 2-methyl-butanol, ethyl acetate, isoamyl acetate, 2,3-butanedione, and 2,3-pentanedione. It was ascertained that the total amount of higher alcohols was higher in the S. cerevisiae control beer compared to all mixed fermentations. Total ester levels were higher in all the mixed culture beers than the control beer. Sensory evaluation showed that all the mixed cultures of S. cerevisiae and T. delbrueckii positively influenced the sensory profile of the beers. Strain Y1031 was the most preferred and was characterized as rich in hop aroma and full bodied. It is therefore a suitable strategy to use T. delbrueckii in mixed fermentations with S. cerevisiae to produce beer with a distinctive flavor. The results demonstrate that, T. delbrueckii strains isolated or commercialized for winemaking can be equally employed as well in brewing.

Categorization and Quantification of Hop Aroma for Targeted Aroma Breeding​

Categorization and Quantification of Hop Aroma for Targeted Aroma Breeding​

STUDY OF THE INFLUENCE OF A HIGHER HOPPING DEGREE OF WORT ON THE FUNCTIONAL PROPERTIES OF ALE BEER

Experiments have been conducted to determine the effect of a higher hopping degree of wort (120 mg/l and 200 mg/l bitter α-acids) on the antioxidant capacity of ale beer. In one of the experimental variants, dry hopping with aromatic hop pellets (3 g/l) was applied. The higher hopping degree of wort did not lead to disturbance in the fermentation process. For beers containing 200 mg/l α-acids, the most significant was the increase in flavonoids (20.6-23.8%) compared to the variant with 120 mg/l α-acids. The polyphenols in highly hopped beer were increased by 6.6-7.1% compared to moderately hopped beer. The content of anthocyanins was not significantly affected by the addition of more hops. Antioxidant activity, expressed as equivalent vitamin C mmol/l, showed an increase of 4-5.2% for highly hopped beers compared to the control variant; when calculated relative to vitamin E, the increase was 5.8-7.5%. All beers were light, with excellent clarity and enhanced hop aroma.

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).

Effect of Czech Hop Varieties on Aroma of Dry-Hopped Lager Beer.

The hoppy aroma in beer is characterized by an overall pleasant profile. The impacts of five Czech hop cultivars, Rubin, Saaz, Vital, Harmonie, and Kazbek, were tested on the hop aroma of the resulting beers, compared with a control beer sample, which was hopped with a commercial hop extract during wort boiling. GC-MS analysis was used for the identification and quantification of aroma-active compounds in the hops and beer. Dry hopping was successful in terms of improving the hoppy aroma in beer. Odorants such as β-myrcene, linalool, geraniol, β-citronellol, humulene epoxide I, and 2-methylbutyl-2-methylpropanoate were found at higher concentrations than the control in all dry-hopped beers. To quantify the success of dry hopping, the transfer rates of hop odorants were calculated. Those of linalool, geraniol and humulene epoxide I were adequate, whereas the transfer rates of polar compounds, e.g., β-myrcene, were relatively low, mostly due to their polarity. Changes in hop oil constituents were clearly notable, with the generation of β-citronellol, the release of other terpene alcohols from their glycosides or oxidation of α-humulene. Yeast metabolism also played an important role in these changes.

Study on the Composition of Hop Terpenes and Terpenoids by Steam Distillation and Effects on Beer Flavor by an Ale Yeast

Model systems of adding three distillates (hop oil, water-soluble aqueous, and residual aqueous) in model wort (buffer) and wort were used to produce model beers and special beers, respectively (with an ale yeast and fermentation at 18 °C). The attributes of hoppy flavor and organoleptic quality were comprised of sustained, surged, generated, or diminished oxygenated compounds and hydrocarbons by yeast biosynthesis in hop essential oil and non-volatile precursors. The matrix of content and instrumental composition of oxygenated terpenoids and hydrocarbons (terpenes and sesquiterpenes) and sensorial profile of model systems was directionally correlated to the matrix and sensory of the early hopped, late hopped, and dry hopped beers. The occurrence of hop aroma profile of the residual aqueous is reminiscent to traditional early kettle hopped beer. The water-soluble volatile components added beer were remarkably close to the distinctive odor profile of late hopped beer. However, dry hopped beer was seemingly a coupling of the hop oil and the water soluble aqueous added beers, but its perception was closer to the latter. The mechanism of the growth of nerol, citronellol, and methyl geranate via a reversed biosynthesis of free linalool by ale yeast and fermentation at 18 °C is contrary to a pathway via geraniol from the hop oil or the water-soluble aqueous. Free linalool was sustained after yeast hydrolysis of linalyl glycoside and related to metabolites in the residual aqueous due to sluggish yeast activity in the model wort (buffer) but not in the wort.

Pilot brewery tests of Czech flavour hop varieties registered in 2022

Seven new Czech “flavour hop” varieties were tested in pilot brewing trials (50 l), in which samples of Ale-style beer were prepared using dry hopping. Essential oils in the beer were determined by fluidized-bed extraction combined with gas chromatography–mass spectrometry. Hop-derived aromas in beer were evaluated by descriptive method. Comparison of terpene essential oils in samples showed differences between hop genotypes and only a partial relationship with the sensory profile of beer. A cluster analysis of hop aromas in beer revealed the relationship between the pairs of Saturn and Pluto; N and Eris; Ceres and Jupiter hop varieties. The submitted results present the sensory properties of these new varieties and are useful for further study of the relationship between chemical and sensory profile of dry hopped beers.

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.