Latest BrewingScience issue out now

Nuremberg | In December 2024, the latest issue of BrewingScience, a scientific online-journal featuring peer-reviewed papers with impact on the brewing industry, was published by Fachverlag Hans Carl. It focuses on hops, and the brief article abstracts below provide a good initial overview of the content.

The latest BrewingScience issue contains the following articles:

Effects of branched-chain fatty acids derived from aged hops on the aroma of beer brewed with flavour hop varieties (C. Tanigawa, S. Otori, K. Takoi, A. Tanigawa and T. Kiyosaki)

Hops stored at room temperature for an extended period are commonly referred to as ‘aged hops’. Degradation of alpha and beta acids occurs during ageing, so the ageing process is accompanied by a significant increase in the concentration of branched-chain fatty acids (BCFAs): isobutyric acid (IBA), isovaleric acid (IVA), and 2-methylbutyric acid (2MBA).

These three compounds, having rancid, cheesy, and/or sweaty flavours, are regarded as “off-flavours”. It was previously reported that BCFAs contained at their threshold levels could enhance the flavour intensity of monoterpene alcohols (linalool, geraniol, and β-citronellol; LGC) and change their aroma profiles. In this study, the behaviours of BCFAs during a 12-months ageing process were compared using five Japanese hop varieties. All BCFAs in the hops increased in all varieties during the total ageing period and a drastic increase was especially observed from 9 to 12 months. The content of linalool gradually decreased but plateaued at relatively high levels. In thiol-containing hops, 3-sulfanyl-4-methylpentan-1-ol (3S4MP) decreased drastically from 6 to 12 months, whereas 4-methyl-4-sulfanylpentan-2-one (4MSP) gradually decreased but was plateaued at relatively high levels. Next, to investigate the sensory effect of aged hops on aroma and taste profile of beer, model beers spiked with several combinations of monoterpene alcohols (LGC), 4MSP, and each BCFA were prepared.

As a result, BCFAs commonly enhanced the characteristics of fruity, fullness, and maturity in the model beer spiking LGC. BCFAs also more enhanced the characteristics of tropical in coexistence with 4MSP. The sensory effect of BCFAs was expected to enhance hop-derived flavour of beer brewed with both geraniol-rich hops and 4MSP-rich hops. However, the sensory tests also showed an increase in rancid characteristics due to the presence of BCFAs. Therefore, test beers were brewed using fresh and aged 4MSP-rich hops.

As a result, although the negative characteristics of rancid gradually increased depending on the dosage of aged hops, the positive characteristics of fruity, tropical, fullness, and maturity increased by mixing only 0.1 g/L of aged hops.

Determination of Variety Dependent “Thiol Impact” Based on LC-MS/MS Analysis of Different Hop Samples Collected Worldwide (C. Schmidt, L. Hoferer and M. Biendl)

Certain volatile thiols are some of the most potent odour-active molecules found in food and beverages including beer. Even contents of a few μg/kg in hops can be high enough to finally result in significant contributions to beer flavour, especially after dry hopping. Most published methods for the determination of free thiols in hops are based on gas chromatographic measurements.

However, liquid chromatography in combination with tandem mass spectrometry (LC-MS/MS), as presented in this study, can also serve for their reliable quantification. This method was used to quantify 4-mercapto-4-methylpentan-2-one (4MMP), 3-mercaptohexan-1-ol (3MH), and 3-mercapto-4-methylpentan-1-ol (3M4MP) in 250 hop samples of 97 different varieties from 12 countries and 5 crop years (2019–2023). Thiol contents show high fluctuation ranges not only dependent on the variety but also on growing area, crop year or harvest date. Based on a large number of single results, it is suggested to create a general classification of varieties by assigning three main categories (low/medium/high) for their “thiol impact” in beer brewing.

New Czech fine aroma hop varieties (Humulus lupulus L.) – Saaz Brilliant, Saaz Comfort and Saaz Shine – have found extensive use in hop growing and beer brewing (V. Nesvadba, J. Olšovská, J. Charvátová, S. Trnková and G. Fritschová)

The renowned Saaz hop variety is primarily used for the production of lager beers. Saaz is the genetic basis for the new Saaz Brilliant, Saaz Comfort and Saaz Shine breeding lines. The present study evaluated the stability and stability trends of the new hop varieties over a period of twenty years based on the content of alpha and beta acids and their ratio. The study also included a comparison between lager beers hopped with the new hop varieties and those hopped with Saaz.

The results of long-term monitoring show that the content of alpha acids of the new aroma hops in the Saaz Brilliant, Saaz Comfort and Saaz Shine breeding lines ranges between 2.16 and 5.36 % w/w, 3.39 and 8.73 % w/w and 2.07 and 7.22 % w/w, respectively. Saaz Brilliant has the highest variability in the content of alpha acids. In contrast, Saaz Shine has the lowest variability and demonstrates an increasing trend in the content of alpha acids. All three hop varieties fall within the category of fine aroma hops, which provide beer with a fine bitterness and a hoppy aroma. Saaz Shine has a lower intensity of bitterness with a fine character and is more suitable for lighter lager beers. In contrast, Saaz Comfort with its higher intensity of bitterness and a longer aftertaste is more fitting for the „Premium Lager” category.

The new hop varieties also demonstrate a very good drought tolerance. Their unique qualities are attracting growing interest, leading to an increase in their cultivation area in the Czech Republic.

Humulus lupulus L. – Yeasts found on wild-growing hop plants and preliminary insights in their brewing characteristics (R. Rehorska, A. Böhm, A. Schöpfer, G. Sauseng, G. Sauseng, F. Prandstätter, G. Almer, C. M. Mayer, M. Grasser, A. Reisner, S. H. Berner and B. Pöllinger-Zierler)

This study focuses on the microfungal community found on hops, and because little data has been available until now, also seeks to increase the body of knowledge on these microfungal communities. Additional benefits may also be gained for brewers who use fresh hops in dry hopping and for beer styles that extensively rely on the technique of dry hopping by providing brewers with insights into which yeast species can enter the beer through hop cones, whether desired or undesired. In this context, the following considerations also come into play: Industrial production of beer requires reproducibility and consistent quality. Wild yeast species are usually undesirable and are considered contaminants. Conventional brewing uses only a few brewer's yeast strains that have been selectively bred over decades.

Despite this, the so-called craft beer revolution has led to the spread of spontaneously fermented beers, for which the natural yeast diversity plays a crucial role. For brewers of such beers, the regional microbiome represents an invaluable resource. The biodiversity of the yeast microbiome that naturally occurs on brewing materials, such as hop cones, as well as its fermentation properties, can provide a competitive advantage. The identified yeast and microfungi species which were found in this study on wild hop plants were: Rhodotorula mucilaginosa, Papiliotrema flavescens, Moesziomyces aphidis, Debaryomyces hansenii, Hanseniaspora uvarum, Fusarium sporotrichioides, Meira spp., Wickerhamomyces spp. and Starmerella spp.

Transfer of Hop Pesticide Residues into Beer during Brewing Process (A. Forster, F. Schüll, A. Gahr, R. Schmidt, A. Faltermeier, R. Kugel and S. Laupheimer)

The use of pesticides in hop cultivation raises concerns about the transfer of pesticide residues (PRs) into beer during brewing. This study investigates the transfer rates (TR) of PRs from hops to beer throughout the brewing process. A spiking technique was employed to simulate elevated pesticide concentrations of relevant active ingredients on hops, with its accuracy assessed against originally contaminated samples.

A key finding was the significant variability in TR, ranging from 0 % to over 70 %, largely dependent on the solubility of individual actives. Special aspects of a brewing process were evaluated. The TRs were similar compared hopping in the brew house and dry hopping. Steps like fermentation, agitation during dry hopping, centrifugation and filtration have a minimal impact on TRs. These results provide valuable insights into the behaviour of PRs during brewing and contribute to a more comprehensive understanding of their transfer, which is crucial for ensuring food safety in beer production. While not OECD-compliant, the spiking method offers a practical approach for studying transfer behaviour of PRs, particularly for compounds that are challenging to detect in originally contaminated samples.

Independent validation of molecular markers for sex determination on diverse sex chromosomes in hops (Humulus lupulus L.) (T. Albrecht, B. Büttner, S.B. Carey, R. Seidenberger, A. Lutz, A. Harkess and S. Gresset)

Humulus lupulus L. is a perennial and dioecious crop important for the beer and food industry. Sex determination in early stages of the breeding cycle is important to secure the selection of female candidates. Phenotypic selection for sex is time consuming and greenhouse capacities are limited generating the demand for an alternative method for early sex screening. Therefore, the need to develop genotypic markers for sex determination is high. Sex-linked markers developed in biparental populations were not applicable across diverse germplasm due to incomplete linkage.

Recent sequence analyses have increased the knowledge about the structure and diversity of the sex chromosomes and newly developed markers are promising for the application in breeding programs. To identify sex-linked markers for the German hop breeding program, we analysed a diversity panel comprising 190 international hop varieties, wild hops and breeding material. SNP (single nucleotide polymorphism) markers were assessed with genotyping by sequencing and a genome-wide association study was performed based on the phenotypic sex expression. Significant SNP markers from the association study were analysed in two validation sets comprising selection candidates. Furthermore, recently published sex-linked markers were analysed in the diversity panel and in both validation sets. Based on both analyses, we were able to validate two SNP markers (“Scaffold_1533_203371763” and SM1) located in the sex determining region of the X and Y chromosomes. Both markers together were able to correctly assign sex to the selection candidates in both validation sets.

Furthermore, genotypic clusters derived from the assays of marker “Scaffold_ 1533_203371763” separated female, monoecious and male plants enabling a more targeted allocation of breeding resources in terms of field and greenhouse space as well as phenotyping and genotyping capacities. This advancement will result in an increased selection intensity and thus progress in developing more resilient hop varieties for a sustainable brewing industry.

You can read the full articles at www.brewingscience.de/.