Journal of the Institute of Brewing

Reflections

David Quain — Wed, 04 Dec 2024 00:00:00 -0800

This issue of Reflections considers some of the challenges with the Journal of the Institute of Brewing switching from a global publisher to being self-published. Whilst some were obvious and (reasonably) easy to address, others were unexpected and were revealed over time. In the ‘unexpected camp’, the visibility of the Journal in university libraries and citation databases was affected with the switch. This was bad news! Publications need to be easily found, read and (hopefully) make an impact. Although a steep learning curve, JIB is now part of EBSCO (used by libraries) and has returned to Scopus (citation database). Going forward, JIB is hopefully joining DOAJ - an index of open access journals. A requirement of the DOAJ application is that the JIB must be digitally archived. It now is, should all be lost with a ‘trigger event’! Comparing the journal’s key performance indicators is a favourite subject, and for this year three of the four process KPIs have improved over 2023. Finally, this issue contains four research papers. One, on the survival of pathogens in non-alcoholic beers, has made an immediate impact and has been downloaded over 500 times in just 30 days from publication.

Impacts of starch breakdown during germination and stewing on aroma formation in crystal malts.

Andrew Foulkes, Irina Bolat, Chris Dodds, David Cook — Wed, 04 Dec 2024 00:00:00 -0800

Why was the work done: Crystal malts are used in brewing to add colour, flavour and mouthfeel to beers. In their manufacture, aroma compounds are formed through thermal flavour generation during roasting of stewed green malt. As part of a wider project to generate novel flavour extracts from roasted products, strategies to maximise aroma compounds in crystal malt were investigated.

How was the work done: Crystal malts were prepared at laboratory/micro-malting scale using a Box-Behnken experimental design where three parameters were varied: (i) germination time (4-6 days), (ii) stewing time at 65^oC (1-24 hours) and (iii) roasting temperature (120-160^oC). The major aroma compounds in the malts were quantified using Solid Phase Micro Extraction Gas Chromatography with Flame Ionisation detection.

What are the main findings: Response surface models are reported which predict the concentration of the quantitatively dominant compounds: acetic acid, furfural, 2-furanmethanol, maltol, HMF, 2,3-dihydro-3,5-dihydroxy-6-methyl-4(H)-pyran-4-one (DDMP), 5-methylfurfural and phenylacetaldehyde as a function of green malt germination time (2-6 days), stewing time (1-24 h) and roasting temperature (120-160^oC). By optimising these factors, the concentration of bulk aroma compounds (sugar degradation products) increased up to sixfold relative to ‘standard’ conditions (four days germination, 1 hour stew at 65^oC and roasting at 140^oC). Optimal conditions for the formation of each compound are discussed in mechanistic terms. An image analysis method using cross polarised light microscopy was developed to quantify the degree of crystallinity of starch granules during stewing. Data indicate that under conventional manufacturing conditions there is a pool of ungelatinised starch in crystal malt kernels which represents an untapped source of aroma compound precursors.

Why is the work important: The results show that varying the production conditions changed the amounts and relative proportions of the main aroma compounds and hence the flavour of crystal malt. This may help maltsters understand differences in the flavour of products from different production facilities. Application of cross polarised light microscopy with image analysis revealed that a proportion of starch remains ungelatinised following standard industry stewing conditions. This demonstrates the potential to generate novel crystal malts with more flavour.

Comparative analysis of four hop cultivars grown in Brazil and the USA by GC-MS-based metabolomics

Guilherme Silva Dias, Marilia Elias Gallon, Leonardo Gobbo-Neto — Wed, 04 Dec 2024 00:00:00 -0800

Why was the work done: Although the third largest beer producer in the world, Brazil currently imports the majority of its hops. A recent development is the cultivation of hops (Humulus lupulus L.) in Brazil. In addition to genetic factors, the chemical composition of hops can exhibit variations due to conditions of cultivation. Accordingly, it is of value to characterise and differentiate hop cultivars grown in Brazil with the same cultivars grown in a long established location such as the United States of America.

How was the work done: Centennial, Chinook, Columbus, and Nugget cultivars grown in Brazil or in the USA were compared by metabolomic analyses of the chemical profiles using gas chromatography coupled to mass spectrometry. Principal component analysis showed sample grouping according to where the hops were grown. Partial Least Squares Discriminant Analysis allowed the characterisation of the main metabolites that discriminated hop samples from the two countries. A total of 31 metabolites were putatively identified, including monoterpenes, sesquiterpenes, oxygenated mono- and sesquiterpenes, esters, alcohols, and ketones.

What are the main findings: There were clear metabolic differences between the same hop varieties grown in Brazil or the USA. The metabolites with the greatest discriminating power for Brazilian hops were trans-α-bergamotene, 2-decanone, and ι-gurjunene, while American hops presented β-copaene, humuladienone, and isopentyl isobutyrate. Notably, trans-α-bergamotene was present in Brazilian hops but absent from American hops.

Why is the work important: This study sheds light on the differences in the chemical composition of hops cultivated in Brazil compared those cultivated in the USA. This knowledge may stimulate new producers and contribute to the development of hop cultivation in Brazil.

Survival of Escherichia coli O157, Salmonella Enteritidis, Bacillus cereus and Clostridium botulinum in non-alcoholic beers

Grzegorz Rachon , Harry Rothera, Sabina O'Reilly, Gail Betts — Wed, 04 Dec 2024 00:00:00 -0800

Why was the work done: To (i) determine whether microbial pathogens were present in packaged alcohol-free and low alcohol beers, (ii) to assess whether pathogens can survive or grow in non-alcoholic beers, and (iii) to determine the impact of pH and bitterness on their growth and survival of pathogens in alcohol-free beer.

How was the work done: : 50 alcohol-free and low alcohol beers, available in the UK, were screened for pathogens and analysed for ABV, pH and bitterness (IBU). One of the alcohol-free beers (with the lowest IBU) was adjusted to 25 and 50 IBU and pH 3.8, 4.2, 4.6 and 4.9. Challenge testing of these beers was performed with Escherichia coli O157, Salmonella Enteritidis, Bacillus cereus and Clostridium botulinum. In addition, the heat resistance (D₆₀ value) of the pathogens, spoilage bacteria and Saccharomyces cerevisiae ascospores in these beers was determined.

What are the main findings: Salmonella, E. coli, Enterobacteriaceae, Bacillus cereus and sulphite reducing clostridia were not found in any of the 50 beers. However, two emerging opportunistic pathogens (Cupriavidus gilardii and Sphingomonas paucimobilis) were found in the low alcohol keg beers. None of the pathogens used in this study could grow in the alcohol-free beer at low pH (pH 3.8). E. coli O157 was unable to grow at pH 4.2 but could grow at pH 4.6 but only with reduced levels of carbon dioxide and increased oxygen. Salmonella Enteritidis was able to grow at pH 4.2 and 4.6 but also with reduced levels of CO₂ and increased O₂. Although Bacillus cereus and C. botulinum were unable to grow in any of the tested conditions, both pathogens were able to survive. Survival and/or growth of the microorganisms was impacted by pH; bitterness had no effect.

Why is the work important: Salmonella Enteritidis and E. coli O157 only grew in alcohol free beer at a higher pH (4.2 and 4.6 for Salmonella and 4.6 for E. coli) together with with reduced levels of CO₂ and increased O₂. This suggests that packaged beer with appreciable levels of carbon dioxide and negligible levels of oxygen will not support the growth of pathogens. However, draught alcohol free beer may be vulnerable to pathogens.

Rapid quantification of isovaleraldehyde in sake by HPLC with post-column fluorescent derivatisation

Wed, 04 Dec 2024 00:00:00 -0800

Why was the work done: Elevated levels of isovaleraldehyde (3-methylbutanal) in sake gives rise to an unfavourable aroma of ‘mureka’ or ‘stuffy smell’. The concentration of isovaleraldehyde is typically higher in unpasteurised than pasteurised sake. Controlling the concentration of isovaleraldehyde in unpasteurised sake remains a major challenge for quality control. As existing methods for the quantification of isovaleraldehyde in sake require specialised sample preparation, there is a need for a simple and precise method.

How was the work done: High-performance liquid chromatography with fluorescence detection and post-column derivatisation (HPLC-PCD-FLD) for determining the isovaleraldehyde content in sake has been developed with optimisation of the separation of peaks and derivatisation of aldehyde compounds. The new method was compared with the established method of headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS).

What are the main findings: The limit of quantification of the new method was 87 µg/L, and accordingly, the HPLC-PCD-FLD method could determine the concentration of isovaleraldehyde in sake below the reported threshold level. The precision of the HPLC-PCD-FLD method for the analysis of sake containing isovaleraldehyde (> threshold level) either matched or was superior to the HS-SPME-GC-MS method.

Why is the work important: The new approach requires only particle removal for sample preparation, with an rapid analysis time (<1 h per sample), and requires a smaller sample volume (≈ 100 µL) than the alternative method (10 mL). These improvements contribute to a simpler and more efficient workflow for routine analysis of isovaleraldehyde in the quality control of sake.