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.     

Prediction of Colloidal Stability of Highly Stabilized Beers by a Modified Chapon Tannoid Content Test

The tannoid content test, introduced by Chapon, is accepted as a recommended MEBAK analytical method for the detection of haze‐forming polyphenols in beer and other intermediates. Under certain conditions, the results can be used directly for predicting the colloidal stability of beer. Its disadvantage is that it does not provide detectable results for beers stabilized by high doses of polyvinylpolypyrrolidone (PVPP). A test modification is proposed that increases the test sensitivity and gives non‐zero results, even for highly stabilized samples that are not measurable by the standard test. The modification is based on adding saturated ammonium sulphate solution (SASS) to the sample to reach 9% saturation (0.5 mL of SASS to 5 mL sample volume) before the actual test performance. The results of the modified test can simply be converted to results obtained by the standard method. Tannoid content correlates linearly with the content of haze‐forming polyphenols and with chill haze produced after defined accelerated aging. In a set of beer samples of one brand having different degrees of stabilization, a high correlation was determined between test results and long‐term colloidal stability. The modified test can be used as a rapid and simple test for checking the stabilization process. It is particularly suitable for Pilsner type beer of long (more than 6 months) colloidal stability controlled by stabilization on the side of polyphenols.     

Roasting of malt and xanthohumol enrichment in beer

The use of commercial roasted malts increases the content of the hop polyphenol xanthohumol (XN) in beer. This carrier effect is caused by high molecular melanoidins from roasted malt. Three roasting trials with different malts were performed in order to study the development of XN enrichment of wort and beer in laboratory and brewing trials. Different colour measurements, malt and flavour analysis, radical formation and antioxidative activity of selected samples were carried out. Furthermore, sensory tests of beers were conducted. During roasting the XN and isoxanthohumol enrichment in wort and beer rose with the roasting intensity of malt until it reached a maximum. The XN content in wort increased linearly with the colour of wort made from the malt samples. In PVPP-treated worts and in filtered beers, the XN content increased exponentially with the colour. After passing through a maximum, both the colour value and XN content in wort and beer decreased. Interestingly, the colour losses were more intensive than the losses of XN in worts and beers. The development of radical formation and the reducing power was linked during roasting. That means reducing groups of melanoidins are responsible for reducing power and prooxidative properties of malts. These functional groups of melanoidins are involved in the development of XN enrichment properties, because a linear correlation between these parameters was found. In conclusion, the roasting regimes showed potential for the development of special malt for the XN enrichment in beer- or malt-based beverages in late roasting stages. The use of this special malt brings more XN with less coloured malt in beer.     

Wheat Variety and Barley Malt Properties: Influence on Haze Intensity and Foam Stability of Wheat Beer

Laboratory wheat beers were brewed with different wheat varieties of different protein content (8.7–14.4%) and with five different barley malts, varying in degree of modification (soluble protein: 3.9–6.9%). In a first series of experiments, it was investigated whether wheat positively influences the foam stability, a major characteristic of wheat beers. NIBEM and Rudin (CO₂) foam analyses revealed that the effect of wheat on foam stability depended on the barley malt used for brewing. When using malt with high foaming potential, wheat exerts a negative influence. However, wheat added to over‐modified malt with less foam promoting factors, ameliorates beer foaming characteristics proving that wheat contains foam active compounds. In addition, Rudin (N₂) values suggested that wheat positively influences foam stability by decreasing liquid drainage, probably caused by a higher beer viscosity and/or a finer foam bubble size distribution. Furthermore, the haze in wheat beers, which is another important quality characteristic of these beers, was investigated. Permanent haze readings of the 40% wheat beers were lower than 1.5 EBC haze units. For 20% wheat beers, an inverse relation between the permanent haze (9.4–19.3 EBC haze units) and the protein content of the wheat was established. The barley malt used for brewing also influenced permanent haze readings. A positive correlation between the modification degree of the malt and the permanent haze intensity was found. It was concluded that the choice of raw materials for wheat beer brewing considerably influences the visual properties of the beer.     

Application of a hop by‐product in brewing: reduction in the level of haze‐active prolamines and improved antioxidant properties of the beer

After supercritical CO₂ extraction of hops or formation of lupulin‐enriched pellets (type 45), polyphenol‐rich by‐products remain. These have some industrial and agricultural applications (preparation of polyphenol extracts and in the production of low‐bitterness beers). In this work, both materials were used in pilot‐scale brewing experiments for the production of beer enriched with polyphenols. Samples of beer made from these residues underwent analyses for haze‐active prolamines, total polyphenols, phenolic monomers, antioxidant capacity, bitterness and colour. An almost identical decrease in the content (from hopped wort to final beer) of the prolamines of approximately 30% was detected in standard beer as well as in the beer prepared from the hop residue (HR 1) after supercritical CO₂ extraction. In contrast, the level of prolamines was reduced by more than 50% in the beer following addition of the hop residue (HR 2) after production of lupulin enriched pellets. Both hop materials contributed to an increase in the antioxidant capacity of the final beer by 21.5 and 11.9%, respectively. Another part of this work was aimed at the investigation of colour and bitterness changes in beers made ??using hop by‐products. Addition of the material HR 2 into the wort caused an increase in colour and in bitterness of the matured beer by 20 and 11% rel., respectively. Copyright © 2014 The Institute of Brewing & Distilling     

FLAVOUR AND HAZE STABILITY DIFFERENCES DUE TO HOP TANNINS IN ALL-MALT PILSNER BEERS BREWED WITH PROANTHOCYANIDIN-FREE MALT

All-malt Pilsner beers were brewed with proanthocyanidin-free malt (ant 13 × 13 × Rupal). Hopping was with n-hexane tannin-free hop extract with or without n-hexane extracted hop residue or with whole leaf hops. The different beers were analysed chemically and presented to an expert panel to detect possible preferences and differences in bitterness and astringency. The impact of hop proantho-cyanidins on haze formation is comparable to that of malt proanthocyanidins. No differences between the beers were found in triangular tests. Statistical analysis of the paired comparison tests showed that hop proanthocyanidins do not contribute to the bitterness of beer since beer brewed with tannin-free hop extract is slightly more bitter than beer brewed with whole leaf hops. No differences in astringency were noted between beers brewed with or without hop proanthocyanidins and it was found that the panel expressed a very slight preference for beer brewed with n-hexane hop extract over beer brewed with both n-hexane hop extract and extracted hop residue.     

The influence of unmalted barley on the oxidative stability of wort and beer

The aim of this study was to investigate the influences of unmalted barley on the brewing process and the quality of the resulting beer‐like beverages, with the main focus on the oxidative stability, using traditional beer analyses, GC‐MS for the determination of aging compounds and electron paramagnetic resonance spectroscopy to determine free radical activity. For the investigation, brews with different barley proportions and 75% barley brews with a colour malt addition, to compensate for a lower colour using barley, were produced. In general, it can be said that beers with a proportion of up to 50% barley achieved a comparable or higher extract yield and final attenuation owing to the combined effectiveness of the malt and microbial enzymes. Although all analytical values were within the normal range according to Methodensammlung der Mitteleuropäischen Brautechnischen Analysenkommission (MEBAK), a slight decrease in total polyphenols and free amino nitrogen content was observed. Also in response to higher barley portions, an increase of higher molecular weight proteins and β‐glucan was detected. Barley is not exposed to heat and oxidative stress in the malting plant, which explains the lower values of the thiobarbituric acid index and colour as an indicator of Maillard reaction products in the resulting wort and beer. Additionally, the results demonstrate a slower increase of aging compounds during beer storage with increasing barley proportions. Furthermore, it was observed that higher barley proportions led to a better oxidative stability indicated by a lower radical generation (T₄₅₀‐value) in wort and an increasing beverage antioxidant index/endogenous antioxidative potential (BAX/EAP value) in the final beverage. The case of ‘barley beers’ showed that the positive effect of barley on the oxidative beer stability was greater than the negative effect of the addition of colour malt, to adjust the colour of a 100% malt beer. In sensory comparison with beer produced with 100% malt, the beers brewed with a barley proportion up to 50% showed a slight flavour preference and up to a 75% equivalent evaluation. Copyright © 2012 The Institute of Brewing & Distilling     

Optimising Beer Stabilisation by the Selective Removal of Tannoids and Sensitive Proteins

Colloidal stabilisation of all malt and adjunct lager beers through selective removal of haze sensitive glycoproteins using silica gel and tannoid polyphenols using polyvinylpolypyrrolidone (PVPP) or a polyvinylpyrrolidone (PVP)‐modified silica gel has been demonstrated during full brewery production. At this scale PVPP and the PVP‐modified silica gel exhibited equivalent binding capability for tannoid polyphenols although PVPP removed additional polyphenolic species. Characterisation of proanthocyanidins following treatment at 4°C with PVPP and the PVP‐modified silica gel silica co‐product confirmed that PVPP removes a wider range of polyphenolics. Both products exhibited poorer polyphenolic binding capability at 4°C as would be expected for a physical adsorption process.     

FLAVOUR AND HAZE STABILITY DIFFERENCES DUE TO HOP AND MALT TANNINS IN ALL-MALT PILSNER BEERS BREWED WITH PROANTHOCYANIDIN-FREE AND WITH REGULAR MALT

All-malt Pilsner beers were brewed with and without hop and malt proanthocyanidins by using regular malt and whole leaf hops as well as proanthocyanidin-free malt and n-hexane tannin-free hop extract. The different beers were analysed chemically and presented to an expert panel to detect possible differences in bitterness and astringency. The impact of proanthocyanidins on the formation of haze was demonstrated clearly. No differences between the beers were found in triangular tests although their levels of total polyphenolics and anthocyanogens differed by about 225 and 85 mg/litre. Statistical analysis of the paired comparison tests showed only very slight differences between beers with or without hop and malt proanthocyanidins. Thus, proanthocyanidin-free beer was considered less than slightly more bitter and astringent than regular beer and there was a very slight preference for the latter.     

Analysis of total polyphenols,bitterness and haze in pale and dark lager beers produced under different mashing and boiling conditions

Malting and brewing processes should be performed under process conditions in a way that minimizes beer bitterness, maximizes polyphenol content and reduces the amount of raw materials ending up in solution in the form of hazes, particles and precipitates. This work examined the influence of different mashing temperature conditions and boiling procedures on the total polyphenol content, bitterness and haze of pale and dark lager beers produced on an industrial scale. Two hop types (hop pellets and/or hop extract) and different hop varieties (Hallertau Magnum, Styrian Goldings, Saaz, Aurora and Sladek) were utilized with varying times of hop addition into the wort. Measurements of total polyphenols, colour, bitterness, alcohol content, CO₂ and pH were carried out on the beer samples. Results showed that pale lager beers had a lower total polyphenol concentration (110–179 mg/L) than dark beers (230–260 mg/L). Using hop extracts instead of hop pellets led to a lower total polyphenol concentration and to less beer foam creation. The change in the proteolytic temperature during mashing only had an influence on the total polyphenol content in the pale lager beer hopped with the pellets. Conducting proteolysis over a 20 min period led to a haze increase in all of the beers produced. In the dark beer, the haze was substantial after just 10 min at 52°C. Copyright © 2015 The Institute of Brewing & Distilling     

Hop proanthocyanidins for the fining of beer

Fining agents are used in the clarification of beers; they help to reduce the time required to sediment suspended yeast cells and ensure the clarity and colloidal stability of beer. Following an adventitious observation during dry‐hopping experiments, we identified a fining activity associated with Saaz hops. Extracts of hop cones were subsequently shown to have the capacity to flocculate yeast and result in their sedimentation. This activity has since been identified in extracts of many different hop varieties and, significantly in spent hops, the co‐product resulting from commercial extraction of hops with either CO₂ or ethanol. Here we illustrate the activity of the novel finings extracted from spent hops following CO₂ extraction of Galena hops. The sediments formed on fining were compact, relative to those obtained when commercial isinglass was used to fine the same beers. The hop extracts were also effective in reducing 90° haze in beers under conditions designed to mimic both cask ale (12 °C) and lager (4 °C) type applications. The compounds responsible for the fining activity appear to be large (30–100 kDa, or more) polyphenols. Analysis of the polyphenols using colourimetric tests indicated the presence of proanthocyanidins. On acidic hydrolysis these generated cyanidin, which would be derived from a polymer composed of catechin and epicatechin subunits. The presence of these materials in spent hops offers the possibility to develop commercial products, with desirable fining properties, from an existing co‐product stream. Furthermore, the finings are derived from a traditional ingredient of the brewing process. Copyright © 2015 The Institute of Brewing & Distilling     

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.     

Formation of 4‐Hydroxyfuranones and their Precursors during Production of Worts and Beers

Laboratory beers and samples taken at each stage of production, were analysed for the flavour active 4‐hydroxyfuranones; 5‐methyl‐4‐hydroxy‐3(2H)‐furanone (MHF), 2,5‐dimethyl‐4‐hydroxy‐3(2H)‐furanone (DMHF) and 5‐(or 2)‐ethyl‐2(or 5)‐methyl‐4‐hydroxy‐3(2H)‐furanone (EMHF). The length and temperature of mashing, the length of boiling, the rate of cooling the worts and the effects of grist composition were investigated to identify the 4‐hydroxyfuranone content of worts and subsequent beers. Fermentation temperature and the use of the stabilising agents, PVPP and Lucilite PC5, on the 4‐hydroxyfuranone content of the beer was also investigated. The results demonstrated that several aspects of beer production procedures affect the furanone content of the beer, but in practice the important factors are grist composition, the rate at which the boiled wort is cooled and fermentation temperature. Fermentation has a major effect on final furanone content as yeast produces both DMHF and EMHF. The results suggest that malt levels of precursor compounds, which can be converted to 4‐hydroxyfuranones by the Maillard reaction or by yeast, may prove to be more important than the quantities of the furanones found in malt in determining the final furanone content of beer. A clearer understanding of the nature of the precursors should allow manipulation of their production and beer furanone content.     

Reducing power of hop cultivars and beer ageing

Since lipid auto-oxidation during wort boiling is a determining for the appearance of staling flavour in aged beers, we have investigated the reducing power of hops added in the boiling kettle. An assay based on the inhibition of linoleic acid oxidation in the presence of an initiator [2,2′-azobis(2-amidino-propane) dihydrochloride=AAPH] enabled us to distinguish hop varieties and conditionings. Large differences in hop flavanoid contents explained the higher antioxidant activity of low-α-acid samples versus bitter varieties and CO₂ hop extracts. As expected, adding hop pellets to the kettle effectively increased the overall reducing activity of wort. Supercritical CO₂ hop extracts had no significant effect due to their extremely low level of polyphenols. The concentration of the very well-known marker of beer ageing, trans-2-nonenal, was lower in boiled wort exhibiting a better reducing power. The AAPH reducing power test applied to hops or worts was thus efficient to predict the nonenal synthesis during boiling. Hop varieties and conditionings emerged from this work as key-parameters for improving the reducing power of wort and the flavour stability of the final product.     

FLAVOUR STABILITY STUDIES: THE USE OF FRACTIONAL FACTORIAL DESIGNS

The number of taste tests that can be undertaken by the average flavour profile panel places a severe constraint on the study of flavour stability. The use of fractional factorial designs has been shown to be an effective approach to this problem. In this work, the effect of eight process variables on both beer flavour and flavour stability have been assessed using only eight experimental beers plus one control. The efficacy of the method is demonstrated by the ease with which the flavour profile panel results can be explained by accepted theories of flavour stability. Thus the variables examined could be divided into three groups. The first group includes headspace air, pasteurization and copper content: an increase in any of these variables leads to a marked increase in oxidized flavours during storage. The second group, which includes sulphur dioxide, PVPP treatment and lupulin (dry hop) addition, reduces oxidation. The remaining variables, proteolytic enzymes and iron content had no obvious effect on oxidation.     

A preliminary study of the quality attributes of a cloudy wheat beer treated by flash pasteurization

Flash pasteurization (37 and 100 pasteurization units, PU) and conventional tunnel pasteurization (15 PU) processing of wheat beers were evaluated by examining their impacts on microorganisms, colour, colloidal haze and flavour stability during 84 days of storage at 20°C. The results revealed that the microbiological stability of 37 and 100 PU flash‐pasteurized beers was comparable with that of the 15 PU sample, and the development of both yeast and lactic acid bacteria was inhibited for 84 days of storage. The conventional tunnel‐pasteurized wheat beer resulted in a higher thermal load relative to the flash‐pasteurized samples based on the results of oxidative stability. These three pasteurized beers showed a similar decrease in haze intensity throughout the storage period. Meanwhile, flash‐pasteurized beers had better colour and colloidal haze stability than the tunnel‐pasteurized beer. It was also found by dynamic light scattering analysis that the temperature in the flash pasteurizer has the desired effect on the protein denaturation and particle size distribution. Therefore, flash pasteurization is a promising method to increase the shelf‐life of wheat beers instead of conventional tunnel pasteurization. Copyright © 2017 The Institute of Brewing & Distilling     

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     

A preliminary study about the influence of high hydrostatic pressure processing on the physicochemical and sensorial properties of a cloudy wheat beer

High hydrostatic pressure (HHP) (400 MPa/15 min, 500 MPa/10 min, 600 MPa/5 min at 20 °C) and heat (60 °C/15 min) processing of wheat beers were evaluated by examining their impacts on microorganisms, colloidal haze, flavour, foam stability and shelf‐life prediction during 84 days of storage at 20 °C. The results obtained showed that the microbiological stability of HHP beers was comparable with heat‐treated samples, and the development of both aerobic bacteria and lactic acid bacteria was inhibited for 84 days of storage. The main parameters of the wheat beer, such as ethanol content, original extract, pH, bitterness and viscosity, were scarcely affected by either treatment compared with the control samples; however, heat pasteurization increased the colour value. Heat‐pasteurized beer resulted in an increase in the phenethyl alcohol concentration and a decrease in isoamyl acetate and ethyl acetate levels compared with the HHP samples. These treatments did not affect the amount of 4‐vinylguaiacol and 4‐vinylphenol in the beer. The HHP‐treated beers had higher colloidal haze and foam stability values than the heat‐pasteurized beers. Dynamic light scattering analysis showed that HHP treatments at 500 MPa/10 min resulted in smaller and more uniform particle sizes, which had a positive effect on beer haze stability during storage. Copyright © 2016 The Institute of Brewing & Distilling     

Possibilities to improve the antioxidative capacity of beer by optimized hopping regimes

Different hopping regimes were evaluated to investigate the effect on the oxidative stability of wort and beer. Compared with a single hop dosage at the beginning of wort boil, it was possible to increase the concentration of α‐acids in pitching wort and beer by applying incremental hop dosage, dry hopping or the use of a pre‐isomerized hop product in combination with an α‐acid extract, which concomitantly resulted in lower iron concentrations and an enhanced flavour stability as indicated by standard wort and beer analyses, atomic absorption spectroscopy, electron spin resonance spectroscopy and sensory analysis of fresh and force‐aged beers. The functional principle of hop dosage variations is explained by saving of α‐acids throughout the wort production process, which yields an increased formation and precipitation of pro‐oxidative acting transition metal ions (e.g. Fe) in α‐acid‐complexes during the whirlpool rest and fermentation. Consequently, fewer reactive oxygen species are generated. Additional laboratory trials simulating wort cooling and beer storage in buffered model solutions proved that un‐isomerized α‐acids are strong iron chelators and confirmed the functional principle of the applied hopping regimes. Negative effects of higher α‐acid contents on fermentation performance and depletion of the zinc concentration, which is an essential nutrient for yeast, could be excluded. Copyright © 2014 The Institute of Brewing & Distilling