Influence of the hopping technology on the storage-induced appearance of staling aldehydes in beer

J. Inst. Brew. 116(4), 381-398, 2010 In this paper, the involvement of iso-alpha-acids in the appearance of stale flavour in beer during storage was examined. Flavour instability upon storage, by far the most important quality problem of beer, may be caused by a multitude of reactions, in particular, the degradation of trans-iso-alpha-acids is pivotal. In order to gain improved understanding of the beer ageing process, the behaviour of the stereoisomers of the bitter acids was studied for the first time in pilot beers at particularly high and low proportions of the trans-iso-alpha-acids concentration relative to the cis-iso-alpha-acids concentration. Therefore, pure trans- respectively cis-isomers were required and obtained on a pilot scale by the separation of trans-iso-alpha-acids as beta-cyclodextrin inclusion complexes from a commercial isomerised hop extract, permitting the quantitative dosage to beer in mg/L amounts. The relationship between the storage-induced degradation of these iso-alpha-acids in authentic beer samples and the increase in staling aldehydes, especially 2-methylpropanal, 2-methylbutanal and 3-methylbutanal, is the subject of further investigations. A remarkable increase in the relative concentration of cis-iso-alpha-acids was observed in the beers bittered with purified trans-iso-alpha-acids, which may be ascribed to partial conversion, i.e., reverse isomerisation, of trans-iso-alpha-acids via alpha-acids into cis-iso-alpha-acids. In spite of the trans-specific degradation observed during ageing, the decomposition of these bitter acids leading to volatile carbonyl compounds is of minor importance. Aldehyde formation as a function of forced ageing was irrespective of the mode of bittering, emphasising that malt quality and the brewing process itself are probably the most important factors regarding the flavour instability of beer

Analytical and sensory assessment of hoppy aroma and bitterness of conventionally hopped and advanced hopped pilsner beers

J. Inst. Brew. 116(4), 445-458, 2010 Analytical and sensory aspects of hoppy aroma of conventionally hopped and advanced hopped pilot Pilsner beers were investigated. Linalool and several sesquiterpenoids were used as analytical markers for the hoppy aroma of the beers. Levels of linalool and sesquiterpenoids in the fresh beers, as well as sensory characteristics of hoppy aroma (intensity and attributed aroma descriptor(s)) clearly depended on the applied hop aromatisation technology and on the type of hop oil fraction used in advanced hopping. The most pronounced hoppy aroma was observed for the advanced bittered beers, either aromatised post-fermentation using a polar hop essence or at the end of wort boiling using pellets (late-hopping). However, all refined hop oil fractions used in this study for advanced aromatisation clearly affected the hoppy aroma impression. Analytical data on staling indicators, combined with sensory evaluations, further suggest that hop oil preparations may also affect flavour stability of the resulting beers in a positive way. In general, it can be concluded that hop aromatisation, whether performed in the advanced or conventional way, appears to mask beer staling, as demonstrated by lower overall sensory ageing scores

Exploring aldehyde release in beer by 4-vinylpyridine and the effect of cysteine addition on the beer's pool of bound aldehydes

As a continuation of our previous work, which concerned the binding of aldehydes to bisulfite and cysteine, this article presents more results on the applicability of 4-vinylpyridine addition to beer prior to analysis aiming at release of aldehydes from these preformed bound states, thus making them quantifiable with the headspace solid-phase microextraction method combined with gas chromatography-mass spectrometry. This article also presents the first results on spiking beer samples with cysteine prior to forced-aging, pointing to the important role of cysteine in beer flavor stability. Both the levels in free and bound aldehydes show a relatively large degree of variation among different beers, but also between marker aldehydes. For some aldehydes (e.g., hexanal), the bound amount was shown to increase rather strongly upon forced beer aging, whereas for others (e.g., 2-methylpropanal), large amounts appeared to already be present in a bound state in the fresh samples. Spiking beer samples with cysteine prior to aging significantly lowered the aldehyde levels compared with nonspiked samples. Flavor stability of the cysteine-spiked beers was thereby greatly improved through aldehyde-cysteine adduct formation. It was further hypothesized that, in addition to efficient binding of aldehydes, cysteine also inhibits the formation of furfural during beer aging from Maillard reaction intermediates

From barley to beer : a quality perspective

Join us for a special a seminar session on Quality of Beer and Hops on Wednesday, September 18, 2019 from 10 am to 12 pm at the Food Science Department (2650 N. Young Ave., Fayetteville, AR 72704) rooms D-1 and D-2. Learn more about hops research collaborations between University of Arkansas and Ghent University. We will have a display of 20 cultivars of hops to evaluate their unique aroma characteristics

How research on alternative grains can boost the brewing industry

How to get research into practice? First get practice into research! The laboratory for Brewing Science and Technology of UGent and HoGent is taking on the challenge of brewing with different unmalted alternative grains in relatively high concentrations. How this will affect the processability, as well as the analytical properties and the sensory profiles of the beers to be produced, will be part of the investigation

Flavour stability of pale lager beer. Chemical-analytical characterisation of critical factors related to wort production and hopping

Beer is often distributed and stored at room temperature, at which stability in terms of brightness and foam is largely under control in contrast to the flavour (combination of odour, aroma, taste and mouthfeel). Already in the early stages of storage of virtually all bottled beers, especially lagers, the disappearance of pleasant fresh beer flavour characteristics is associated with the accelerated development of unwanted ageing flavours. Given the increasing importance of export and the ever intensifying competition in the international market, a prolonged stability of the beer flavour is however a prerequisite. The distribution and particularly the export of beers can then be broadened while consumers are minimally confronted with changes in flavour and drinkability, even upon prolonged storage time prior to consumption. An optimised flavour stability is equally important for beers intended for the domestic market, as it is the best guarantee for maintaining the drinkability, which is with a direct impact on consumption very important in the light of a declining pale lager beer consumption. Some brewers do in fact operate a cold-chain, expensive though it may be. Consequently, prolonging the flavour stability of beer remains a major concern for each modern brewery.With their off-flavour character and very low thresholds, aldehydes play a key role in the sensory perception of aged beer flavours, since their concentration increase, even at μg/L levels, coincides with the appearance and intensity of organoleptic defects. Several reaction pathways give rise to these ageing compounds during beer production and storage, but knowledge on their proportional role is far from complete.Next to the significant decline in beer bitterness, the decomposition of in particular trans-iso-alfa-acids into a series of non-volatile cyclic compounds contributes to a harsh lingering bitterness upon ageing. The flavour shelf life of beers brewed with a strongly reduced level of trans-isomers can thus be extended with regard to bitterness intensity and quality. However, the impact that the iso-alfa-acids degradation has on the formation of ageing aldehydes is currently only exploited to a very limited extent. It remains unclear whether ageing aldehydes would develop less in beers with enhanced levels of cis-iso-alfa-acids, since the cis-isomers are distinctly less susceptible to degradation compared to their trans-counterparts.Against this background, this doctoral study aimed to generate new insights into the relationship between iso-alfa-acids degradation and the formation of ageing aldehydes, with focus on the marked instability of trans-iso-alfa-acids, in order to determine critical factors related to wort production and hopping for an improved beer flavour stability.A number of aldehydes were selected as beer flavour instability markers, i.e. 2-methylpropanal, 2-methylbutanal, 3-methylbutanal, methional, benzaldehyde, phenylacetaldehyde, furfural, hexanaland trans-2-nonenal. Accurate analytical measurement of these aldehydes in a complex matrix such as beer requires highly specific extraction and detection techniques to obtain the necessary sensitivity and selectivity. Based on the properties of the compounds of interest, headspace solid phase microextraction with on-fibre O-(2,3,4,5,6-pentafluorobenzyl)-hydroxylamine (PFBHA) derivatisation in combination with capillary gas chromatography-negative chemical ionisation mass spectrometry (CGC-NCI-MS) was the technique of choice in this PhD study. The unique characteristics of the NCI spectra of aldehyde PFBHA-oxime derivatives provided excellent selectivity and sensitivity for measurement of the selected marker aldehydes, even when present at trace levels. The developed methodology was successfully applied to study the formation of aldehydes in fresh and forced aged beers.Given the pronounced instability of trans-iso-alfa-acids compared to their cis-counterparts, the evaluation of their potential specific impact on the formation of ageing aldehydes is necessary. Therefore both trans- and cis-iso-alfa-acids were required in their pure form and separated from a commercial isomerised hop extract by formation of trans-iso-alfa-acids/ß-cyclodextrin (ß-CD) complexes. The implemented preparative-scale separation procedure yielded the required amounts of isolated trans- and cis-iso-alfa-acids in a purity of 94% and 98%, respectively, for addition to model solutions and repeated trials of beer.The possible formation of ageing aldehydes arising from iso-alfa-acids degradation upon dark storage, was initially investigated in model solutions containing bitter acids or/and amino acids or/and xylose. In this way, the huge complexity of the beer matrix was originally evaded, allowing us to reveal the proportional contribution of each of the constituents to the formation of hop-derived aldehydes, Strecker aldehydes, and furfural, respectively. The involvement of different bitter acids (trans- vs. cis-iso-alfa-acids and iso-alfa-acids vs. dihydro- and tetrahydroiso-alfa-acids) in these reactions was evaluated, based upon their reported relative stability.The relationship between the bittering and the aldehyde formation was subsequently further explored in beer. In a comparative study, the impact of the bitter acids degradation on the aldehyde increase upon forced ageing in the dark was repeatedly studied in identically prepared pilot pale lager beers conventionally bittered (pellets, CO2-extract), bittered with iso-alfa-acids end boiling, and post-fermentation bittered with exclusively iso-alfa-acids, enriched trans-iso-alfa-acids, enriched cis-iso-alfa-acids, dihydroiso-alfa-acids and tetrahydroiso-alfa-acids, respectively, and compared with the aldehyde levels in the corresponding unhopped beers.For the first time, the differential behaviour upon ageing of trans- and cis-iso-alfa-acids was studied separately in model solution as well as in the beermatrix. Even though an increase in the aldehyde levels was monitored both in model solutions and aged beer samples, the suggested chemical pathways for aldehydes as degradation products of iso-alfa-acids were derived from the model experiments. The observed increase in the levels of marker aldehydes was only related to the conversion of iso-alfa-acids during storage in the model solutions. 2-Methylpropanal was identified as a volatile, direct degradation product of both cis- and trans-iso-alfa-acids without the involvement of amino acids and/or xylose in these model experiments. The conversion of both cis- and trans-iso-alfa-acids was unmistakably influenced by the oxygen levels of the model solutions. In the presence of amino acids, this led to the formation of 2-methylbutanal, 3-methylbutanal, methional, and phenylacetaldehyde. This has been reported for the first time, and is explained as a Strecker-like degradation of the amino acids by a non-volatile oxidation product of both cis- and trans-iso-alfa-acids, the hydroxy-allo-iso-alfa-acids. These alfa-unsaturated carbonyl compounds are postulated as reactants for the Strecker-like degradation of amino acids in model solution, delivering the corresponding Strecker aldehydes.However, the contribution of this reaction to the increase in Strecker aldehydes in the aged iso-bittered beers was found negligible. cis-Iso-alfa-acids showed increased stability in beer compared to the model solutions, indicating less oxidative degradation. Despite the fact that clear differences in the stability of the bitter compounds between the nine specific bittered beers were observed, it was shown that the increase in aldehydes is irrespective of the bittering. In unhopped beer in fact an at least equally high increase in aldehydes was observed upon storage, so that the presence and conversion of, in particular, trans-iso-alfa-acids in the beer matrix can not be considered as a critical factor for the formation of aldehydes during beer ageing. On the basis of beers made with another pale malt it was further demonstrated that the malt and wort production should be considered as critical factors for the flavour stability of beer, as deduced from the higher aldehyde levels in the fresh and aged beers.In conclusion, through a comparative study of the impact of different types of bitter acids on aldehyde formation upon beer storage, the opportunities of using highly enriched cis-iso-alfa-acids preparations in brewing practice to prolong beer flavour stability were explored. The results obtained in this study created attractive new insights into the degradation of iso-alfa-acids and proved that under oxidative conditions, both cis- and trans-iso-alfa-acids are a source of Strecker aldehydes through a postulated Strecker-like reaction between oxidative iso-alfa-acids degradation products, the hydroxy-allo-iso-alfa-acids, and amino acids. However, this reaction was of no or at least less importance in the beer matrixat low oxygen concentrations, since the aldehyde increase upon ageing was irrespective of the applied bittering. Still, enriched cis-iso-alfa-acids can be utilised in beer in view of an enhanced bitterness stability, in the absence of light and with low-oxygen bottling. Therefore, the upscaling of the enrichment of cis-iso-alfa-acids from a mixture of cis- and trans-iso-alfa-acids opens up new perspectives. Moreover, cis-iso-alfa-acids are more bitter than the corresponding trans-isomers, so for the same bitterness intensity, less cis-iso-alfa-acids will be needed, which also yields an additional economic advantage. This doctoral study argues for an improved quality control of the used malt with the aim of reducing the aldehyde content in fresh and aged beer, and suggests to the brewer some points to reduce aldehydes production during brewing and beer storage, such as mashing-in conditions, limiting heat load (rapid wort filtration) and oxygen-free bottling.nrpages: 288status: publishe

Cheers to more fresh beers : why freshness matters

Beer is pretty great, but fresh beer is even better! Already in the early storage stages of almost all bottled beers, the disappearance of pleasant fresh beer flavour characteristics is accompanied by the accelerated development of undesirable staling flavours. Given the increasing importance of export and the ever-intensifying competition in the international market, long-term fresh beer flavour stability is a prerequisite. This talk will merge you into the science behind beer flavour stability. Not knowing how to achieve beer flavour stability becomes the major obstacle you will want to overcome

A practical approach to excellent beers with alternative cereals

One of the major trends in beer consumption is the continued preference for quality over quantity. To meet this consumer demand and remain competitive, brewers have experimented in many ways to expand their product range, such as the use of hops, different fermentations, addition of spices or fruits, barrel aging, etc. A less explored and therefore promising way in the search for new and innovative flavors, is the partial replacement of barley malt on the grain bill by less common adjuncts. However, a change in basic ingredients has major implications for both the brewing process and the final beer. Over the past two years, in collaboration with a diverse group of industrial brewers, suppliers, maltsters, etc., we have conducted a major research project under the name AlterBrew on the integration of 10 different unmalted alternative cereals and pseudocereals into the brewing process. The adjuncts studied were the ancient wheat types einkorn, emmer, spelt and khorasan; the pseudocereals quinoa, amaranth and buckwheat; and three other cereals being sorghum, teff and tritordeum. First, these cereals and pseudocereals were evaluated and compared for their brewing-relevant properties. Second, wort production was evaluated using 40% alternative cereals and pseudocereals, after which experimental beers were brewed on a 20-liter scale. In the third stage, the three most promising cereals, khorasan, teff and einkorn, were selected for scale-up to pilot scale and were weighed against three references, namely barley malt, raw barley, and wheat. The influence of replacing 40% of the grain bill with the alternative cereals on the brewing process when using a thin-bed filter and a lauter tun, respectively, and on the final beer quality obtained was investigated. Filtration was faster with the thin-bed filter, and a 40% replacement was found to be too much for brewing with khorasan and teff in combination with the lauter tun. Thin-bed filtration of the mash with 40% khorasan was faster than with the references and the fastest overall. Brewing with 40% einkorn resulted in clogging of the thin-bed filter when using a grist-to-water ratio of 1:2.2. A larger amount of water was required to produce the beers. When using 40% teff, the thin-bed filtration rate was also faster than the references, but brewing with teff required a pregelatinization step. The quality parameters of the beers produced with the alternative cereals were generally similar to those of the reference beers. Nevertheless, a lower overall yield and a lower extract value were observed when brewing with these adjuncts. The beers were then aged at 30°C to study their flavor stability over a period of at least 120 days. The increase of marker aldehydes and the decrease of hop bitter acids were monitored