BrewingScience issue November/December 2025 out now

Nuremberg | The latest BrewingScience issue 11/12 2025 focuses on hops. It contains an article on the influence of hop seeds on the analytical properties and sensory quality of beer; a chemical and sensory characterization of new czech flavor hop varieties; an article on the combined effect of rooting medium and biostimulant application on morphological traits of micropropagated hop plantlets; and the phytochemical and sensory comparison of Czech and world flavour hop cultivars. The brief article abstracts below provide a good initial overview of the content.

Influence of hop seeds on the analytical properties and sensory quality of beer (F. Schüll, A. Forster, A. Gahr)

The EU certification system distinguishes between seedless and seeded hops. The vast majority of hops produced within the EU belong to the category of hops without seeds, which allows a maximum seed content of 2 % (w/w). However, with increasingly restrictive herbicide regulations and the resulting growing difficulty of controlling male plants, compliance with this limit may become challenging in the future. Hop seeds are generally regarded as undesirable in brewing because of their high fat content, which promotes oxidative degradation and may impair beer foam stability.

Previous studies on the influence of hop seeds on beer quality have produced contradictory results. In this work, the impact of hop seeds on beer quality was assessed through brewing trials. Lager beers were produced with additions of 50 and 70 g/hl hop seeds during wort boiling and after primary fermentation. The addition of hop seeds showed no measurable effects on foam stability or sensory properties. Even in long-term storage tests (6 months at 30 °C), no differences in quality were detected between beers brewed with and without seeds. The only noticeable change was a slightly increased alcohol content, likely resulting from amylolytic enzyme activity in the seeds. Seed proportions above the EU limit of 2 % therefore do not appear to negatively affect beer quality.

Nevertheless, hop seeds do not contain relevant amounts of bitter compounds and thus offer no technological value in brewing. Instead, they merely contribute additional weight, increasing costs for harvest and subsequent processing steps such as pellet production. Moreover, seed formation raises the plant’s nutrient demand during cultivation. Taken together, a high seed content is incompatible with economically and environmentally sustainable hop production.

Chemical and sensory characterization of new czech flavor hop varieties (Juno, Saturn, Pluto, Ceres, Eris, and Jupiter) with evaluation of drought and disease resistance (V. Nesvadba, J. Olšovská, J. Charvatová, S. Trnková)

This study characterizes six new Czech flavor hop cultivars – Juno, Saturn, Pluto, Ceres, Eris, and Jupiter – using long-term datasets (2015–2025) that integrate chemistry, sensory profiling, and stress-resistance testing. Across cultivars, alpha acids were consistently moderate (4.6–7.2% w/w), while total hop oils spanned 0.68–1.57% w/w. These compact ranges, coupled with specific aroma profiles, support their suitability namely for dry hopping.

Sensory results showed clear differentiation: Juno, Saturn, and Ceres expressed fruit-forward profiles; Pluto and Eris were citrus-driven; Jupiter exhibited a heavier woody-spicy character. Stress-tolerance assessments highlighted robust agronomic performance in several cultivars. Juno, Saturn, and Ceres combined favorable aroma with improved drought tolerance; among breeding lines tested in parallel, drought resistance frequently exceeded that of registered checks. Disease screening against downy mildew (Pseudoperonospora humuli) revealed high resistance in Saturn and very good resistance in Juno, Eris, and Ceres, whereas Pluto and Jupiter were less resistant. Overall, the new Czech flavor hops deliver modern aroma signatures with moderate alpha acids and practical advantages in drought and disease resilience. These traits have already driven adoption in Czech craft breweries and position the cultivars as versatile options for lager and top-fermented styles, particularly in dry-hopped applications.

Combined effect of rooting medium and biostimulant application on morphological traits of micropropagated hop plantlets (P. Loreti, R. Ruggeri, A. Rossini, C. Silvestri, R. Picchio, F. Rossini)

Establishing vigorous and healthy plants is the first requisite for the future success of a new hopyard. Although hop micropropagation has been extensively studied, little information is available on subsequent ex vitro rooting and acclimatization phase. For example, materials and practices used to obtain an excellent hop plantlet ready for the field are often not referenced.

The major challenge is to produce well-rooted plants without excessively boosting the vegetative growth. New substrates (alternative to peat) and treatments (alternative to synthetic plant hormones) are likely required to address this issue and to increase the sustainability of the process. With this aim, we used micropropagated plantlets of cultivar Cascade and Nugget to assess the combined effect of rooting medium and biostimulant application on root and shoot development during two hardening periods: i) acclimatization in glasshouse, and ii) acclimatization in open air.

Two growing media were tested: i) a standard peat-based substrate (control treatment), and ii) an experimental substrate, consisting of a mixture of the standard substrate and woodchip compost. Extracts of seaweed Codium fragile (Suringar) Hariot and plant Opuntia ficus-barbarica A. Berger were used as biostimulant agent. The experiments were set up in a completely randomized design with three replicates. Survival rate, shoot and root traits as well as rhizome development were determined.

At the end of the study, the foliar biostimulant significantly increased root growth (21% in length and 46% in weight) and rhizome length (+46%), while it had a moderate effect on shoot development. Hop cultivars tested in our study highlighted a very different way to allocate plant biomass during the hardening period, with Nugget having a root-to-shoot ratio twofold higher than Cascade. Finally, even though the experimental substrate did not affect plant traits during the first acclimatization period, it had a strong negative effect during the acclimatization in open air. Our findings provide practical guidance for nursery managers seeking to produce high-quality hop plantlets using sustainable materials and treatments.

Phytochemical and sensory comparison of Czech and world flavour hop cultivars (J. Patzak, V. Nesvadba, J. Charvátová, G. Fritschová, J. Hervert, K. Krofta)

In the new millennium, a lot of hop flavour cultivars with a unique “varietal aroma” have been bred and widely used for a dry hopping of beers. Seven flavour hop cultivars were also registered in the Czech Republic in recent years. Essential oils, depending on their concentrations, combinations and threshold levels, are responsible for diverse aroma and flavours of hop cultivars in dry cones and beers. In this study, we evaluated qualitative essential oils parameters and sensory aroma profiles in dry cones of 7 Czech and 23 world flavour hop cultivars by multivariate principal component analysis (PCA), which divides cultivars to quadrants. The Czech flavour cultivars Juno and Jupiter were placed in the first quadrant, influenced by higher geranyl Acetate and methyl-4-8-decadienoate contents. The Kazbek, Ceres, Eris, Pluto and Saturn cultivars were grouped in the second quadrant, influenced by higher 2-MeBu-isobutyrate and geranyl isobutyrate contents, in essential oils analyses.

However, in sensory aroma analyses, the Jupiter cultivar was placed in the first quadrant due to its woody aroma, whereas the Juno and Pluto cultivars were placed in the second quadrant due to their floral and grassy aromas. The Saturn cultivar was placed in the third quadrant due to a fruity aroma and the Kazbek, Ceres and Eris cultivars were grouped in the fourth quadrant due to their citrusy aroma. 7 Czech and 11 world flavour hop cultivars were also compared by sensory aroma analyses in dry hopping brewing tests. There was no correlation found between cultivar sensory aroma profiles in dry cones and beers, and differences and discrepancies in flavours for all of them. We proved that Czech hop flavour cultivars provided original sensory aroma profiles in beers and that they are useful for breweries in different beer styles.