Evaluation of Variety, Maturity, and Farm on the Concentrations of Monoterpene Diglycosides and Hop Volatile/Nonvolatile Composition in Five Humulus lupulus Cultivars

Behavior of Geranic Acid and Related Compounds during Hop (Humulus lupulus L.) Cone Maturation: Comparison among Sorachi Ace, Its Daughters, and Other Hop Varieties

Numerous hop varieties with unique aromas─flavor hops─have been developed to enhance beer flavor. Sorachi Ace (bred by Sapporo Breweries Ltd.) is the mother of several characteristic flavor hop varieties including Hokuto Ace and Furano Special. Our previous research found significant levels of geranic acid in Sorachi Ace hops and beers. Owing to its acidic nature, this compound remains abundant throughout the brewing process, including wort boiling and fermentation. Moreover, when geranic acid is combined with other hop-derived compounds, it contributes to the characteristic varietal aroma of Sorachi Ace beers. This study investigated the behavior of geraniol-related compounds (geraniol, geranial, geranic acid, and methyl geranate) during extended harvest periods in eight hop varieties, including Sorachi Ace and its daughters. Hops were harvested at different days after flowering (DAF): from 45 DAF (normal harvest) to 85 DAF. Hokuto Ace and Furano Special displayed lower geranic acid levels than Sorachi Ace, although its geranic acid-accumulation trait was more or less inherited. The conversion of geranic acid to methyl geranate progressed in most hop varieties, except for Sorachi Ace and its daughters. In these varieties, esterification was strongly suppressed, especially in Sorachi Ace and Hokuto Ace, leading to geranic acid accumulation with extended harvest time. These results support a geranic acid accumulation mechanism in these varieties. In Cascade, Columbus, and Magnum hops, geranic acid was scarcely detected, whereas geraniol, geranial, and methyl geranate levels increased from 45 DAF to 65 DAF. Conversely, in Sorachi Ace and its daughter hops, geraniol and geranial levels gradually decreased with extended harvest, suggesting that geranic acid accumulation may suppress the biosynthesis of these compounds.

Comparison of polyfunctional thiol, element, and total essential oil contents in 32 hop varieties from different countries

Volatile thiol 3-mercaptohexan-1-ol (3MH) and particularly 4-mercapto-4-methylpentan-2-one (4MMP) are highly potent flavour compounds in hops. For the determination, a simple and robust stable isotope dilution LC-MS/MS method was developed and applied to 32 hop varieties worldwide from harvest years 2019 and 2020. Limit of detection, precision, and recovery were 0.15 μg/kg, 10%, and 97-108%, respectively. Levels of 3MH and 4MMP ranged from 1.9 to 79.2 μg/kg and from undetectable to 37.1 μg/kg, respectively. Citra, Mosaic, and Strata were rich in both thiols. ICP analyses revealed, that variation of potassium content between the two harvest years was inversely correlated with that of manganese and rubidium (|r| ≥ 0.89) among 12 US varieties excluding Citra and Mosaic. Total essential oil content (0.34-2.7 mL/100 g) was inversely correlated with calcium content (|r| ≥ 0.65). Greatly varying thiol levels depending on variety, region and harvest year might lead to differing flavour results in beer.

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.

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.

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.

Effect of "Late Harvest" of Hops (Humulus lupulus L.) on the Contents of Volatile Thiols in Furano Beauty, Furano Magical, and Cascade Varieties

In recent years, many hop varieties with unique aromas, so-called "flavor hops", have been bred and grown. Here, we investigated the effect of late-harvested hops using three flavor hop varieties; Furano Beauty, Furano Magical, and Cascade. The sample hops were harvested at different days after flowering (DAF): DAF 45 (normal harvest), DAF 65, DAF 75, and DAF 85. We measured the volatile thiols in sample cones. The results indicated that 4-methyl-4-sulfanylpentane-2-one contents showed almost no change or a slightly decrease with a delay in harvest, whereas 3-sulfanyl-4-methylpentan-1-ol (3S4MP) content in late-harvested samples increased several fold in comparison with normal-harvested samples. Additionally, 3S4MP contents in the beers brewed with DAF 65 samples were several times higher than those using DAF 45 ones. From these results, we propose a new method to control 3S4MP content in hop cones by changing its harvest date.

Brewing Efficacy of Non-Conventional Saccharomyces Non-cerevisiae Yeasts

Consumer demands for new sensory experiences have driven the research of unconventional yeasts in beer. While much research exists on the use of various common Saccharomyces cerevisiae strains as well as non-Saccharomyces yeasts, there exists a gap in knowledge regarding other non-cerevisiae Saccharomyces species in the fermentation of beer, in addition to S. pastorianus. Here, five distinct species of Saccharomyces from the UC Davis Phaff Yeast Culture Collection, as well as one interspecies hybrid from Fermentis, were chosen to ferment 40 L pilot-scale beers. S. kudriavzevii, S. mikatae, S. paradoxus, S. bayanus, and S. uvarum yeasts were used to ferment wort in duplicate pairs, with one fermenter in each pair receiving 10 g/L dry-hop during fermentation. Analytical measurements were made each day of fermentation and compared to controls of SafAle™ US-05 and SafLager™ W 34/70 for commercial brewing parameters of interest. Finished beers were also analyzed for aroma, taste, and mouthfeel to determine the flavor of each yeast as it pertains to brewing potential. All beers exhibited spicy characteristics, likely from the presence of phenols; dry-hopping increased fruit notes while also increasing perceived bitterness and astringency. All of the species in this study displayed great brewing potential, and might be an ideal addition to beer depending on a brewery’s desire to experiment with flavor and willingness to bring a new yeast into their production environment.