The chemistry of beer aging – a critical review

Currently, the main quality problem of beer is the change of its chemical composition during storage, which alters the sensory properties. A variety of flavours may arise, depending on the beer type and the storage conditions. In contrast to some wines, beer aging is usually considered negative for flavour quality. The main focus of research on beer aging has been the study of the cardboard-flavoured component (E)-2-nonenal and its formation by lipid oxidation. Other stale flavours are less described, but may be at least as important for the overall sensory impression of aged beer. Their origin has been increasingly investigated in recent years. This review summarizes current knowledge about the chemical origin of various aging flavours and the reaction mechanisms responsible for their formation. Furthermore, the relationship between the production process and beer flavour stability is discussed.     

Analytical‐Sensory Determination of Potential Flavour Deficiencies of Light Beers

Although currently light beers have a high market share in the US, this beer style is still not accepted on the European continent because light beers are considered watery, mainly on account of lack of mouthfeel. In this paper, the flavour quality, including flavour stability, of five commercial light beers was evaluated in comparison with their corresponding pilsner beers derived from the same breweries. Through detailed physico‐chemical and sensory evaluation, followed by multivariate data analysis, the fresh beers could be differentiated according to their origin (US or European) and beer style (light or pilsner). Potential flavour deficiencies of fresh light beers were determined as too much sweetness, lack of bitterness, and especially reduced fullness. As a result, the fresh light beers were less preferred than their corresponding pilsner. Upon ageing, the light beers were generally less flavour stable than their pilsner counterparts. This is mainly ascribed to increased sensory perception of cardboard and ribes staling flavours in most aged light beers. Nevertheless, based on detailed analytical/sensory investigation, it was clearly demonstrated that one of the light beers involved in this study showed enhanced flavour stability with respect to all other beers, including the pilsner beers.     

主要啤酒老化物质的来源与控制

综述了主要啤酒风味老化物质是5-羟甲基糠醛(5-HMF)与反-2-任烯醛的来源、检测方法．以及啤酒生产过程中控制其含量的措施。     

The Influence of Hopping on Formation of Carbonyl Compounds During Storage of Beer

Improving beer flavour stability is an important brewing goal. Pilot scale brewing trials (50 L) were performed that focused on the determination of the influence of hop pellet dosage and dosage timing on carbonyl compounds in stored beer. The reducing activity of experimental worts, beers and stored beers appeared to depend on the hop pellet dose. Brews with lower amounts of hop antioxidants showed an enhanced formation of carbonyl compounds over the course of beer storage. A correlation between DPPH reducing activity and the content of some carbonyls, including the important markers 2‐furfural and (E)‐2‐nonenal, was found. Fresh and aged beers hopped by different amounts of hop pellet doses were clearly distinguishable according to their carbonyl content using Cluster analysis. Results of the sensorial analysis corresponded to the analytical criteria values. Results of this study bring further evidence of the indispensable impact of hop antioxidants on the suppression of undesirable carbonyl compound formation in the course of beer staling, which can be significant in beers hopped by aroma hops. However, hop antioxidants are only one of many factors affecting beer staling.     

The Role of Malt and Hop Polyphenols in Beer Quality,Flavour and Haze Stability

Pilot‐scale brewing trials of a 12°P pale lager beer were conducted to look at the effect of a modified dose of hop and malt polyphenols on haze, flavour quality, and stability. Results confirmed that malt polyphenols, and particularly hop polyphenols, in the course of wort boiling, improved reducing activity values and the carbonyl content in fresh and stored beers. Hop polyphenols significantly increased reducing activity and decreased the formation of carbonyls (TBA value) in fresh and stored beer. Reduced content of malt polyphenols, combined with the use of hop CO₂ extract, caused an increase in the TBA value in beer. PVPP stabilized beers tended to be lower in reducing activity. Both malt and hop polyphenols affected the intensity of “harsh taste” in fresh beers and a significant influence from PVPP stabilization of beer was not observed. The staling degree of forced‐aged beers depended on the polyphenol content in the brewhouse. Both hop and malt polyphenols had a positive impact on flavour stability. PVPP treatment of beer had a positive effect on the flavour stability of heat‐aged beers. Polyphenols, especially hop polyphenols, slowed down flavour deterioration during the nine month storage period, but the primary effect was seen during the first four months of storage. Storage trials did not show any unambiguous effects for PVPP stabilization on beer flavour stability. Results confirmed the negative impact of malt and hop polyphenols on haze stability, and PVPP stabilization minimized differences in shelf life prediction values between beers prepared with the modified dose of polyphenols.     

高效液相色谱同时测定啤酒中的5-羟甲基糠醛和糠醛

采用高效液相色谱（HPLC）同时分析啤酒中的5-羟甲基糠醛（HMF）和糠醛（2-F）。采用0．1％乙酸-乙腈为流动相,等度洗脱,样品中的5-HMF和2-F在10min内达到基线分离。啤酒样品直接进样测定,5-HMF和2-F的RSD分别为0．70％和1．09％（n=5）;平均加标回收率分别为101％和103％（n=3）。     

CAPRYLIC FLAVOUR AS A FEATURE OF BEER FLAVOUR

Caprylic flavour is part of the distinctive overall flavour of a large proportion of beers in trade. The flavour occurs in the majority of lager beers and in about 20% of ales. It is correlated with the levels of octanoic acid and decanoic acid present in beer. Lager yeasts (S. uvarum) tend to liberate larger amounts of these two fatty acids during fermentation than do ale yeasts (S. cerevisiae). The flavour significance of these acids has been determined by correlating the results of sensory and instrumental analyses and also by adding the purified acids to beer. Implications of these two methods for assessing the flavour significance of chemical constituents of a complex product are discussed.     

Influence of hop harvest date of the ‘Mandarina Bavaria’ hop variety on the sensory evaluation of dry‐hopped top‐fermented beer

To impart a special hop aroma to beer, dry‐hopping is a technique that is becoming more and more popular with commercial breweries. Nevertheless, until now little was known about the factors that influence the reproducibility (and consistent product quality) of dry‐hopping with flavour varieties. One factor that could influence the sensory impressions and aroma profile compositions of dry‐hopped beers is the hop harvest date. Therefore, to determine the effects of different harvest dates of the flavour variety ‘Mandarina Bavaria’ on the aroma of top‐fermented beer, laboratory‐scale dry‐hopping trials were performed. Besides tasting sessions of brewed beers, relative quantities of selected hop‐derived, as well as beer‐originated aroma compounds, were investigated by headspace–solid‐phase microextraction–gas chromatography–mass spectrometry. Duo–trio tests between the beers hopped with pellets of different harvest dates showed no significant differences (α = 0.05) between them. In addition, these beers had similar profiles in a five‐point profile tasting scheme. On the other hand, relative concentrations of some hop‐derived aroma compounds – especially myrcene, which is known to be able to contribute to beer flavour – increased corresponding to a later harvest date, while beer originated volatiles were not different between the beers. Analytical results combined with the results of sensory evaluations led to the conclusion that the harvest date of Mandarina Bavaria was not a dominant factor in the dry‐hopping aroma of top‐fermented beers. High amounts of fermentation by‐products are likely responsible for masking effects resulting in no sensory distinctness between the samples with different hop aroma compound concentrations. Copyright © 2016 The Institute of Brewing & Distilling     

DISCRIMINANT ANALYSIS OF SENSORY AND INSTRUMENTAL DATA ON BEER

Stepwise discriminant analysis has been used to examine sensory and instrumental data on forty six different brands of ale from five brewing companies. The beers were classified also according to four evenly spaced bands of original gravity within the range 1·030 to 1·050. Two samples of each beer from brews several months apart were analysed. Eighty of the beers were correctly assigned to brewing companies from data on four sensory and five instrumental parameters. The most important of these parameters were iso-amyl alcohol content and caprylic flavour, both of which relate to products of fermentation. Eighty six of the beers were correctly classified into gravity bands using data on thirteen sensory parameters relating to the beer flavours. In this case the three most important parameters were body (palate-fullness), viscous (thick) mouthfeel and aldehydic/estery character.     

Assessment of endogenous antioxidative compounds and antioxidant activities of lager beers

BACKGROUND: Flavour stability is increasingly becoming the limiting factor in the shelf life of beer. Increasing the antioxidant activity of beer itself could suppress the rate of oxidative reaction and improve the flavour stability of beer. This report describes the levels of phenolic compounds, melanoidins and sulfur dioxide, and antioxidant activities of 40 lager beers. The relationships between antioxidative compounds and antioxidant activity were elucidated by multivariate analysis techniques. RESULTS: The results showed that the total phenolic content and the melanoidins content correlated well (P < 0.05) with antioxidant activity, while there was no significant correlation (P > 0.05) between total sulfur dioxide content and antioxidant activity. Satisfactory discrimination among beer samples with significantly different antioxidant activity was achieved by principal component analysis. Results from stepwise linear regression further demonstrated that different antioxidative components responsible for antioxidant activity were dependent on the assay used. The phenolic compound group is by far the most antioxidative compounds in beer and total phenolic content, melanoidins and sulfur dioxide together made a 22–68% contribution to the antioxidant activities of beers. CONCLUSION: Therefore, it might be an efficient means for brewers to increase total phenolic content during brewing for improvement in flavour stability of the final beer. © 2012 Society of Chemical Industry     

Flavour Instability of Pale Lager Beers: Determination of Analytical Markers in Relation to Sensory Ageing

Flavour changes of six Belgian pale lager beers were studied in order to estimate the importance of different parameters and reactions in relation to the ageing process. An attempt was made to link analytical data with sensory evaluation using multivariate statistical analysis. Partial least squares regression techniques (PLSR) were employed on the analytical and sensory data. As apparent from the PLSR model, significant indicators of lager beer ageing are aldehyde markers (especially total aldehydes, furfural, hexanal, 2‐methylpropanal, 2‐methylbutanal, and 3‐methylbutanal), cold and permanent haze, and beer colour. Conversely, compounds or parameters that load negatively in the PLSR model for beer ageing are trans‐isohumulones, cis‐isohumulones, total bitterness, the T/C‐ratio, polyphenolic markers (especially proanthocyanidins), the flavanoid content, and, to a lesser extent, the TB‐index and reducing power (TRAP). The integrated analytical‐sensorial methodology is proposed as a useful tool for evaluation of the flavour instability of pale lager beers.     

Impact of wood species on microbial community composition,beer chemistry and sensory characteristics during barrel-ageing of beer

Barrel-ageing of conventionally fermented beers is becoming increasingly popular in recent years, but only very little is known about the underlying process. In this study, we show that wood species significantly affects the bacterial community composition, beer chemistry and sensory characteristics throughout 38 weeks of barrel-ageing. Whereas the microbial communities of oak- and acacia-aged beer became dominated by Pediococcus damnosus and Brettanomyces bruxellensis, beer aged in oak barrels also contained a large fraction of Acetobacter sp. (29.34%) and to a lesser extent Paenibacillus sp. (2.74%) that were almost undetected in acacia-aged beer. Oak barrels also imparted substantial concentrations of eugenol, lactones and vanillin, while acacia-aged beer contained high concentrations of total polyphenols and β-glucan, which also translated into different sensory perceptions. Altogether, our results provide novel insights into the barrel-ageing process of beer, and may pave the way for a new generation of beers with a noteworthy flavour complexity.     

Breeding of lipoxygenase‐1‐less malting barley variety ‘Satuiku 2 go’

The lipoxygenase‐1‐less (LOX‐less) trait has positive effects on beer quality, in particular, improvement of flavour stability related to the reduction of beer‐deteriorating substances such as trans‐2‐nonenal. ‘Ryohfu’ is the only spring‐sown malting barley variety grown in Hokkaido, located in the northern part of Japan, and has been used in the Japanese brewing industry for over 20 years. ‘Satuiku 2 go’ was developed as the first LOX‐less malting barley variety in Japan by successive back‐crossing with molecular marker‐assisted selection to introduce the LOX‐less trait into the recurrent parent ‘Ryohfu’. The agronomic performance and general malt quality of ‘Satuiku 2 go’ were almost equivalent to those of ‘Ryohfu’. Wort and beer analyses at the pilot‐scale brewing trial indicated that the LOX‐less trait had little effect on the general characteristics. In contrast, the beers made from ‘Satuiku 2 go’ malt exhibited reduced levels of trans‐2‐nonenal and trihydroxyoctadecenoic acid. The sensory evaluation demonstrated the superiority of ‘Satuiku 2 go’ beers stored under differing conditions in terms of staleness. It can be concluded that the LOX‐less trait was effective in different genetic backgrounds of the recurrent parents used for the development of LOX‐less malting barley varieties. Copyright © 2018 The Institute of Brewing & Distilling     

Flavour Impact of Aged Beers*

Using a gas chromatography olfactometry (GCO) technique, it has been possible to identify a number of flavour impact components of fresh, naturally aged and forced aged lager. One of the benefits of this technique is that a wide range of volatile flavour components, for example esters, aldehydes, sulphur compounds and lactones can be examined within a single analysis. Together with appropriate conventional chemical analysis for aldehydes and sensory analysis, it has also been possible to relate perceived changes in overall flavour balance to some specific changes in aldehyde levels during ageing. In this way, time dependent changes in the levels of methional, phenylacetaldehyde, 4-methoxybenzaldehyde, octanal, (E)-2-nonenal have been indicated. GCO allows for the convenient detection of flavour components whose contribution may remain undetected by current conventional chemical analysis but which may play a key role in determining the flavour impact of aged beers.     

Identification of substances responsible for the ‘sawdust’ aroma in oak wood

The unpleasant ‘sawdust’ odour sometimes found in wines aged in new barrels was studied by gas chromatography olfactory detection and mass spectrometry. A particular aromatic zone has several chromatographic peaks, corresponding to certain characteristic odours which can be detected by smelling the gas effluent. These include the subtle rancid, weedy odour of ‘sawdust’. Various carbonyl components have been identified in this particular zone. These include (E)-2-nonenal, 3-octen-1-one, (E)-2-octenal and 1-decanal. These molecules are the primary cause of disagreeable oak wood odours. By measuring (E)-2-nonenal in wines, after derivation by O-(2,3,4,5-pentafluobenzyl)-hydroxilamine (PFBOA), it was possible to correlate the concentration of this unsaturated aldehyde with the intensity of the ‘sawdust’ character noted in tasting. The possible explanations for the presence of these carbonyl compounds are debatable. The carbonyl content varied from one wood sample to another. However, controling the toasting of the wood, both in the laboratory and in the cooperage, produced a major reduction in the extractable (E)-2-nonenal content and eradicated the ‘sawdust’ character of the wine. © 1998 SCI.     

Impact of colour adjustment on flavour stability of pale lager beers with a range of distinct colouring agents

The impact of colour adjustment on the flavour stability of five pale lager beers with a range of colouring agents such as specialty malts, colouring beer and artificial caramel colourant was investigated. The research focused on determination of the endogenous anti-oxidative potential (EAP) of the beer samples using a novel Electron Spin Resonance (ESR) method. The results were correlated with the concentration levels of a portfolio of compounds formed during beer ageing, which were detected and quantified by GC–MS. The beer samples were also assessed by the ICBD sensory panel. Additionally, the quantification of organic radicals of the specialty malts and the roasted barley were conducted by ESR (whole intact kernel and milling fraction measurement). Based on the results of this holistic approach, a colouring agent was identified that enhanced the flavour stability of pale lagers based on the final beer’s physical-, chemical-, and sensory-properties.     

Volatile compounds isolated from rice beers brewed with three medicinal plants

The volatile compounds and physicochemical properties of rice beers brewed with three medicinal plants, namely Acanthopanax senticosus (Siberian ginseng), Scutellaria baicalensis (baikal skullcap) and Cornus officinalis (Japanese cornel) were analysed. The rice beers were produced and fermented from unhulled ground rice, malt, and medicinal plant extracts. The medicinal plant extracts, used at 5 and 10 % (v/v) were blended with wort before fermentation. Compared with a draft beer fermented without rice, the rice beers had lower levels of pH, acidity, amino acid content and reducing sugars. Of the rice beers, the beer with the addition of 10% Japanese cornel had the highest colour value and foam stability. The volatile compounds of the rice beers were extracted using a solvent‐assisted flavour evaporation apparatus and analysed by gas chromatography–mass spectrometry. The rice beer with 10% Siberian ginseng showed the most diverse volatile profile, in that 54 kinds of volatile compounds were detected. The rice beer with 10% Japanese cornel had the highest relative amount of volatile chemicals of all of the rice beers. Lactones such as γ‐hexalactone, γ‐nonalactone and γ‐decalactone were detected in all of the rice beers. Copyright © 2013 The Institute of Brewing & Distilling