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.     

TANNING PROPERTIES OF FLAVANOLS IN BARLEY AND HOPS MEASURED BY REACTION WITH CINCHONINE SULPHATE IN RELATION TO HAZE FORMATION IN BEER

The flavanoid polyphenol extracts from barley and hops were each separated into six fractions by adsorption chromatography on Sephadex LH20. These fractions were further characterised by several analytical methods, including high-performance liquid chromatography and a colorimetric measurement of polymerisation index. The tanning powers of the fractions were graded according to their reactivities with cinchonine sulphate solution in a standardised turbidometric test. Whereas, almost 75% of the flavanols from Ark Royal barley were non-tanning oligomers almost 96% of the flavanols from Bullion hops were polymeric tannins. Reactivity of most of the barley flavanols with cinchonine sulphate was increased greatly by oxidation with peroxidase and hydrogen peroxide. Some effects of polymerisation, caused by enzyme action or by exposure to air, on oxidisable polyphenols (non-tannins) were measured using (+)-catechin, procyanidin B3 and prodelphinidin B3 in model systems. These, and other measurements on experimental and commercial beers indicated that oxidation of simple flavanols from barley produced polymers with tanning properties. In contrast, the hop flavanols when extracted apparently in their native forms, were capable of co-precipitating with polypeptides in beer. Treatment of beers with different stabilising agents, such as Polyclar AT and silica hydrogel, retarded haze formation by restricting ‘protein-polyphenol’ interactions.     

THE NITROGENOUS COMPLEXES OF HAZE AND FOAM AND THEIR MEASUREMENT

Earlier work and a review of recent studies have led to the view that the complex nitrogenous substances of beers are all, to some extent, irreversibly co-complexed either with glucose polymers or with polyphenols, or with both. Where amino-groups are still free, there can, in addition, be reversible combination with complex acids in worts and beers. The proportions of these different types of co-complex are considered to have important effects on beer properties, so that methods for the measurement of the amounts present are regarded as essential. With this as objective, it has been found that the relatively unmodified “free-amino” nitrogenous complexes, as well as those co-complexed with polyphenols, can be precipitated by suitable acidic dyes. The resulting precipitates can then be dissolved to give a simple and rapid colorimetric measurement of the amounts of these complexes present. By using the specific reagent polyvinyl pyrrolidone (AT) to absorb and remove the polyphenolic co-complexes, the remaining “free-amino” nitrogenous complexes can be precipitated alone, so that separate measures of both types can be obtained. Using bromophenol blue as the dye, some precipitation, mainly of the higher molecular weight fractions, occurs around pH 5 and by progressively lowering the pH to 3, or by progressively increasing the dye concentration, larger and larger amounts are precipitated to give a spectrum of the nitrogenous complexes present. Using a method based on these findings, wide variations have been found in the amount of different complexes in different beers. Studies have been made of the selective migration of complexes into foam and of the changes occuring during increase of haze. The methods have also been used to study the changes produced by proteolytic enzymes and by silica gel absorption, as well as those produced by changes in the nitrogen content of malts used. In one stout, dye-precipitable complexes are present in very small amounts. It appears that only non-reactive “crypto-nitrogenous” co-complexes persist after the prolonged mashing period used: a rapid method of measurement has been found for these also.     

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.     

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     

Evaluating haze formation in flavoured lager beers using a range of forcing methods

Haze formation is a quality problem that can affect a wide range of drinks for a number of different reasons. Although well‐characterized in traditional beers, the emergence of novel beer‐based beverages has led to the potential for chemical interactions that can result in the precipitation of haze material. In this study, the haze formation in 19 commercially available flavoured lager beers was investigated. The chemical parameters of each of the drinks were measured and haze formation was induced through three forcing tests, developed for use in both the beer and wine industries, as well as using a novel forcing test, designed for this study. Several of the products were particularly susceptible to a number of haze forcing tests and the EBC temperature cycling and the Wine Forcing (70°C) tests were found to generate the most forced haze (measured at 90 and 13° scatter angles, respectively) in these products. There was no overall correlation between the drinks' chemical parameters and their susceptibility to haze formation. However, a weak, but statistically significant, correlation (p  = 0.044) was observed between the concentration of polyphenols in the products and the presence of haze measured by 90° scatter angle. Copyright © 2017 The Institute of Brewing & Distilling     

Beer Polypeptides and Silica Gel Part I. Polypeptides Involved in Haze Formation

Beer contains approximately 500 mg/L protein depending on the brewing procedures employed. This protein is in the form of polypeptides, the majority of which lie within the 10–40 kD size range. Some of these polypeptides are responsible for causing colloidal haze, others enhance foam stability and the remainder appear to have no function in beer except to contribute to mouth‐feel. The polypeptides responsible for haze formation are those that can combine with polyphenols to produce a visible cloudy haze. This is undesirable as it can have a negative effect on the beer's shelf life. One way to reduce this effect is to remove these polypeptides using silica gels. It is important that this removal is selective, and the desirable foam enhancing polypeptides are not removed. Data will be presented to show that beer polypeptides are glycosylated and that silica preferentially adsorbs glycoproteins, particularly those with protein components rich in the amino acid proline. The molecular size and composition of glycoproteins recovered from untreated beer, cooked adjunct, silica exposed to beer and beer aged for one year are presented. Glycoproteins involved in foam, and the apparently functionless polypeptides, will be discussed in a subsequent paper.     

The chemical components in malt associated with haze formation in beer

In bright beer, haze formation is a serious quality problem, which reduces beer storage and shelf life. In this study, haze‐active proteins, alcohol chill haze formation ability, α‐amylase activity, the contents of total polyphenol, protein and its fractions and amino acids were analysed using 23 barley accessions to investigate the relationship between the quality components in the malt and the haze character in beer. The results showed that there were largely genotypic variations for all examined traits among the 23 barley accessions. However, there was no significant correlation between the haze character and α‐amylase activity. All haze characteristics were significantly and positively correlated with total protein content, albumin, globulin and the hordein content, as well as the glutamic acid (glutamine), proline and phenylalanine content, and were not correlated with total polyphenols. A model describing the relationship between the chill haze in the beer and the protein content in the malt was developed. Copyright © 2016 The Institute of Brewing & Distilling     

Haze formation in beverages

The most frequent cause of hazes in beverages is due to protein-polyphenol interaction. Proteins that bind polyphenols contain proline, and the more proline, the greater the haze-forming activity. Polyphenols that cause haze have at least two sites that can bind to proteins; this enables them to cross-link proteins together and results in insoluble particles that scatter light. Protein-polyphenol interaction is non-covalent and, at least initially, reversible. The size of haze particles and the haze intensity are both affected by the ratio of haze-active (HA) polyphenol to HA protein. Alcohol content and pH also exert strong influences. Particle size in a model system does not vary smoothly as conditions change; rather shifts in the proportions of particles of a few discrete sizes are seen. Haze development occurs over time in packaged products. In clear beverages a treatment (fining, adsorption or ultrafiltration) is normally applied to reduce the concentration of either HA protein or HA polyphenol in order to delay the onset of haze formation beyond the intended product shelf life. A nephelometer observation gives a good indication of the amount of haze people can perceive.     

A Discussion of Polyphenols in Beer Physical and Flavour Stability

Generally referred to as polyphenols (PPs), beer flavonoids such as the flavan‐3‐ols and their condensed products, the proantho‐cyanidins, represent a class of readily oxidizable compounds capable of hindering or preventing the oxidation of other molecules present in beer. Flavan‐3‐ol and proanthocyanidin capacity to improve oxidative stability has been well established in other food systems, and thus these antioxidants have recently gained significant consideration as potential beer flavour modifiers and/or stabilizers. The duality of their presence in beer is that PPs complex with proteins in the beer matrix to form temporary and permanent hazes. Undesirable physical instability caused by PP‐protein interactions can be resolved via use of adsorptive resins such as polyvinylpyrrolidine. While there is no doubt that polyphenol removal increases beer shelf stability in terms of haze formation, the impact of polyphenol removal on beer flavour remains unresolved. This review discusses the sources, content and impact of polyphenol presence and removal on beer physical and flavour stability.     

A SCIENTIFIC BASIS FOR BEER FOAM FORMATION AND CLING

The most complex types of nitrogen compound in beer (here termed “proteoses”) are, when not combined with polyphenols, highly surface active and hence concentrate in the foam. With unhopped beer, the foam is of the “liquid-viscous” type, which eventually drains and collapses leaving no residual solids. The iso-α-acids in hopped beers are also surface-active, so they too are concentrated in the foam. At the corresponding concentration in bulk solution the solubility limits of some isohumulates* are exceeded. Thus we believe that solids are similarly formed in the bubble films, so that these are reinforced and stiffened to give “cling”. One consequence of the increased concentration of iso-α-acids in the foam is that there can be precipitation of iron, nickel, cobalt and zinc isohumulates. This results in concentration of these metals in foam. The most significant finding is that the concentration of both proteoses and iso-α-acids in the foam exceeds the bulk solubility limits and results in the formation of proteose-isohumulate salts which make the main contribution to the solid reinforcement of bubble films. These findings make it possible to explain satisfactorily “lacing” or “cling” and also isohumulone losses (a) during boiling and trub separation, (b) during post-fermentation bittering, and (c) during any subsequent foam formation. An explanation is also provided why losses of bitterness and of head retention are linked. Consequently, linked recovery of both bitterness and head retention can occur, as has been found is some recent fermentation improvements, such as continuous fermentation.     

Cognitive and emotional differentiators for beer: An exploratory study focusing on “uniqueness”

The current explosion of micro-brewed beers has created a category that varies greatly in style, quality, ingredients, sensory attributes and brand images. To establish a niche in this market, brewers often differentiate their product through the tailoring of sensory characteristics of the beer or its brand image. However, many other consumer-based attitudinal and cognitive variables can be used to differentiate beers. These include perceived familiarity, novelty and situational appropriateness, as well as attitudinal and emotional product associations. In the present study, these variables were evaluated for their effectiveness in differentiating a variety of New Zealand beers. Two sets of 8 beers were evaluated by consumers (n = 203 beer enthusiasts) by: (i) classifying them for familiarity/novelty, (ii) answering attitudinal questions, (iii) assessing appropriateness for 15 common use situations and (iv) identifying emotional associations. Results showed each of the variables to be important differentiators. Although perceived familiarity and novelty were inversely related, familiarity better differentiated among the familiar beers, while novelty better differentiated the novel beers. Attitudinal data showed the most familiar beers to be “ordinary”, “boring” and “simple”, and those judged novel to be “unusual”, “intriguing”, and “complex”. In spite of this, “appealing” beers could be found among both the familiar and novel samples. Situational appropriateness data showed familiar beers to be appropriate for “casual” and “everyday” situations, while novel beers were most appropriate for “special occasions”. Lastly, emotion data showed the beers to differ along “active/passive” and “hedonic” dimensions, with familiar beers having passive emotional associations and novel beers having more active associations. In summary, this novel, consumer-based multi-faceted approach was extremely effective in differentiating among beers and provided useful insights for the identification of what may be considered “unique” beers.     

THE ESTIMATION AND SIGNIFICANCE OF CATECHIN AND DIMERIC CATECHIN IN BEER

A gas-liquid chromatographic method for the estimation of monomeric and dimeric catechin in beer is described. This method has been used to estimate the concentrations of these compounds in a number of beers, which were found to contain 0·5 to 8·0 ppm of monomeric catechin and up to 22·0 ppm of dimeric catechin. Beers bottled with a high level of air in the headspace can have a long shelf-life providing the level of dimeric polyphenols is low. The shelf-lives of beers which contain high concentrations of dimers are very sensitive to the levels of air in the headspace. At the levels found, monomeric catechin has no significant effect on haze whether or not headspace air is present.     

EFFECT OF VARIOUS POLYPHENOLS ON THE RATE OF HAZE FORMATION IN BEER

The effect of the addition of a range of monomeric, dimeric and polymeric polyphenols to beer on the rate of haze formation has been examined. Monomeric polyphenols had no significant effect on haze formation. The addition to beer of dimeric or polymeric polyphenols caused a large increase in the rate of haze formation.     

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     

Expertise and memory for beers and beer olfactory compounds

Do beer experts have better recognition memory for beers than novices? And can recognition memory for beers be predicted on the basis of recognition memory for beer odor compounds? We compared the memory performance of “beer experts” and novices in two recognition tasks. The first task was performed ortho- and retronasally with beers, and the second orthonasally with beer odor compounds. As a control we also compared the performance of “experts” and novices on an identification task and a same/different discrimination task. “Beer experts” outperformed novices in both the identification task and the recognition memory task with both beers and odor compounds, but only for beers they had been trained on (familiar beers), and regardless of the type of odors (familiar vs. unfamiliar). “Experts” were only marginally superior in the beer discrimination task. This suggests that the experts’ advantage in recognition memory is likely to have its source in more efficient coding and retrieval in long-term memory, rather than in better perceptual ability. No significant correlation was found between odor and beer memory performance, which suggests that, during training, “experts” might develop independent memory structures for odor compounds and for beers.     

Turbidity and Haze Formation in Beer — Insights and Overview

Beer is a complex mixture of over 450 constituents. In addition, it contains macromolecules such as proteins, nucleic acids, polysaccharides and lipids. Proteins influence the entire brewing process with regard to enzymes, which degrade starch, β‐glucans and proteins; with protein‐protein linkages that stabilize foam and are responsible for mouthfeel and flavour stability; and in combination with polyphenols, thought to form haze. With this complexity, problems in processability are as various as the constituents. Several substances in beer are responsible for haze formation. Organic components such as proteins, polyphenols and carbohydrates (α‐glucans, β‐glucans) are known to form haze. In addition, inorganic particles such as filter aids and label remains can cause increased turbidity. In this article only non‐microbiological induced hazes are described. Many studies have been conducted on the identification of haze and foam active components in beer. Hence the aim of this work was to survey the different possibilities of haze formation and for haze identification. A summary is provided on methods for haze identification including dyeing methods, microscopic analyses and size exclusion chromatography.     

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.     

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     

苹果汁中活性蛋白的性质及其稳定化处理研究进展

苹果汁中活性蛋白质 (HAP)是澄清苹果汁产生混浊沉淀的重要原因之一 ,疏水性氨基酸易于和多酚聚集 ,形成混浊。苹果汁中不同浓度的活性蛋白质与低分子的多酚以及简单酚所引起混浊的反应机理不同 ;活性蛋白质的种类、分子结构、反应的时间、温度、反应体系的 pH、无机离子及其离子强度对浑浊的产生有重要影响。单宁酸、膨润土、硅溶胶和聚乙烯聚吡咯烷酮 (PVPP)是有效的稳定化处理措施。