Free radical reactions in beer during pasteurization

Oxidative reactions during beer pasterization were studied using chemiluminescence (CL) and electron spin resonance (ESR) analyses. the CL production of beer was acclerated by pasteurization and the maximum CL intensity appeared sooner than that in non-pasteurized beer. Beers pasteurized with 15–30 pasteurization units (P.U) had the same CL producing activities as the non-pasteurized beers stored at 20°C for 6–10 days. Free radicals were produced and some of them were consumed by beer oxidation during pasteurization. It seems that free radicals were consumed by beer oxidation during pasteurization. It seems that free radical reactions occur in beer during pasteurization and that the degree of oxidation during pasteurization generally corresponded to that of non-pasteurized beer stored at room temperature for about 1 wee.     

A STUDY OF BEER STALING USING CHEMILUNINESCENCE ANALYSIS

The chemiluninescence (CL) analysis has been used to study beer staling. Several types of commercial Japanese beers were stored at 37°C and their CL development analysed at 60°C. The CL level in beer developed as the beer was stored to reach a maximum level and then decreased. The sum of the CL intensities for the first 1 hour showed a good relationship with staling degree as assessed in mean panel scores. It is postulated that the deterioration rates of beers might be assessed from the CL producing patterns in the fresh beers before storage. The presence of sulfite in beer depressed the CL production during its storage indicating that there is some contribution of sulfite to flavour stability due to its inhibitory effect on radical reactions in beer.     

Evaluation of Beer Deterioration by Chemiluminescence

The application of chemiluminescence (CL) analysis for the evaluation of staling beer was studied. Commercial Japanese lager beer was stored at 30°C, 37°C, and 60°C and its CL generation was analyzed at 60°C. The CL production was accelerated to a greater degree and its intensity reached maximum level more rapidly with increase in incubation temperature and/or time. The sum of the CL intensity for the first 1 hr showed a good relationship with staling degree in mean flavor panel scores. Therefore, CL determination may be useful for evaluating oxidation deterioration of beer.     

Yeast Proteolytic Activity During High and Low Gravity Wort Fermentations and its Effect on Head Retention

The aim was to discover the effect of high gravity brewing on yeast protease activity during fermentation, on the loss of hydrophobic polypeptides from wort during fermentation, and on the foam stability of stored beer. The hydrophobic polypeptide content of low (10° Plato) gravity worts showed a steady decline throughout fermentation, but for the 20° Plato wort there was a rapid decline over the first 8 days of fermentation, followed by little change over the remaining period. The decrease in hydrophobic polypeptides was greater in the high gravity fermentation. Proteinase A increased during fermentations with the highest levels being present at the end of fermentations. High gravity fermentations exhibited levels of yeast protease that from the 3rd to 11th day of fermentation were at least twice the values of the low gravity fermentations. The high gravity brewed beer contained significantly higher levels of proteinase A activity than the low gravity brewed beer. The inclusion of FERMCAP™, an antifoam, in high gravity wort did not affect either the hydrophobic polypeptide levels or foam stability of the resultant beer. This suggests that proteinase A, rather than fermenter foaming, must be the major contributor to the lack of foam stability of high gravity brewed beer. Head retention measurements conducted on the high and low gravity brewed bottled beers, over a five month period, demonstrated a steady decline in foam stability for both beers. The declines in head retention did not occur in high and low gravity beers that had been pasteurised.     

硅凝胶对提高啤酒非生物稳定性的应用研究

本试验研究是利用硅凝胶吸附高分子蛋白质的特点,以提高啤酒非生物稳定性的应用研究。试验筛选出适用于啤酒的,经特定制备方法制得的C-Ⅰ型硅凝胶,其对啤酒中高分子含氮物质具有较强的选择性吸附作用,可有效地提高啤酒的非生物稳定性,且不改变啤酒的其它纽分和外观质量。试验结果表明:适宜的吸附处理时间为5～30分钟,吸附温度为0℃,起到了提高啤酒非生物稳定性和不改变啤酒其它质量指标的作用。     

啤酒生产贮存过程中风味物质的探讨

啤酒生产过程中,氧化还原酶与啤酒风味陈化紧密相关,其主要原因就是氧化。因此,氧化还原酶对啤酒风味具有不可忽视的影响。高级醇是啤酒中一种重要的风味物质。影响高级醇含量的有酵母菌种、接种量、麦汁浓度,以及发酵的温度等。在成品啤酒贮存过程中,由于单多酚能够氧化生成聚多酚而造成啤酒涩味和苦味。因此,减少成品啤酒中的单多酚含量,有利于啤酒的风味和质量。     

高效液相色谱-Ru（bipy）32+-Ce（SO4）2化学发光体系检测啤酒中的亚硫酸钠

在酸性条件下,Ce(SO4)2氧化Ru(bipy)32+时,在Na2SO3存在下,对该化学发光具有很强的增敏作用,据此建立通过HPLC分离、用化学发光检测器测定亚硫酸钠的方法。在优化的实验条件下,测定亚硫酸钠的线性范围为2.0×10-6～5.0×10-4g/mL,方法的检出限为6.0×10-7g/mL,定量下限为2.0×10-6g/mL,线性回归方程:△I=3.578c+19.721(c:g/mL;r2=0.9984),对5.0×10-5g/mL亚硫酸钠进行了11次平行测定,其相对标准偏差为3.7%。该法已成功的运用于实际啤酒样中亚硫酸钠的含量。     

Determination and fractionation of metals in beer: a review.

Major, minor and trace metals are important in beer fermentation since they supply the appropriate environment for yeast growth and influence yeast metabolism. A real concern is the content of copper (Cu) and iron (Fe), which are involved in beer conditioning and ageing through reactions resulting in formation of reactive oxygen species. The reactive oxygen species readily oxidize organic compounds present in beer, changing the quality of foaming and the flavour stability of beer. In view of brewing technology and beer processing, knowledge regarding functions of metals and their speciation in brewing liquors and beer is of special significance. Metals in beer also have a certain nutritional importance, but their actual effect related to beer consumption depends on the type of species they form with low and high molecular mass organic ligands which naturally occur in beer. This review covers the determination and fractionation of metals in beer using atomic spectrometry methods. Special attention is drawn to the role of metals in beer and brewing, possible metal associations, methods of beer preparation before analysis on the total metal content, and approaches to metal partitioning in beer.     

Determination and fractionation of metals in beer: A review

Major, minor and trace metals are important in beer fermentation since they supply the appropriate environment for yeast growth and influence yeast metabolism. A real concern is the content of copper (Cu) and iron (Fe), which are involved in beer conditioning and ageing through reactions resulting in formation of reactive oxygen species. The reactive oxygen species readily oxidize organic compounds present in beer, changing the quality of foaming and the flavour stability of beer. In view of brewing technology and beer processing, knowledge regarding functions of metals and their speciation in brewing liquors and beer is of special significance. Metals in beer also have a certain nutritional importance, but their actual effect related to beer consumption depends on the type of species they form with low and high molecular mass organic ligands which naturally occur in beer. This review covers the determination and fractionation of metals in beer using atomic spectrometry methods. Special attention is drawn to the role of metals in beer and brewing, possible metal associations, methods of beer preparation before analysis on the total metal content, and approaches to metal partitioning in beer.     

Determination and fractionation of metals in beer: a review

Major, minor and trace metals are important in beer fermentation since they supply the appropriate environment for yeast growth and influence yeast metabolism. A real concern is the content of copper (Cu) and iron (Fe), which are involved in beer conditioning and ageing through reactions resulting in formation of reactive oxygen species. The reactive oxygen species readily oxidize organic compounds present in beer, changing the quality of foaming and the flavour stability of beer. In view of brewing technology and beer processing, knowledge regarding functions of metals and their speciation in brewing liquors and beer is of special significance. Metals in beer also have a certain nutritional importance, but their actual effect related to beer consumption depends on the type of species they form with low and high molecular mass organic ligands which naturally occur in beer. This review covers the determination and fractionation of metals in beer using atomic spectrometry methods. Special attention is drawn to the role of metals in beer and brewing, possible metal associations, methods of beer preparation before analysis on the total metal content, and approaches to metal partitioning in beer.     

THE CONTRIBUTION OF DEXTRINS TO BEER SENSORY PROPERTIES PART I. MOUTHFEEL

The effect of dextrins on the mouthfeel of beer was assessed using instrumental and sensory techniques. By measuring the viscosity of beer with a rheogoniometer, it was shown that beer is a newtonian fluid, i.e., shear stress increased linearly with shear rate. A capillary viscometer and a rheogoniometer gave viscosity measurements that did not differ significantly for six beers ranging in viscosity from 1.1 to 2.6 centipoise (cP). In carbonated beer, the amount of dextrins needed to produce an increase in viscosity detectable by judges was 52 g/litre, which raised the viscosity by 0.31 cP as measured by capillary viscometry. Since beer usually contains between 10 and 50 g/litre of dextrins, it is concluded that dextrins are not the sole determinant of beer viscosity.     

Influence of Pasteurising Intensity on Beer Flavour Stability

While it is preferred that flavour improves during the beer maturation process, formation of undesirable flavours inevitably occurs during beer storage. Beer ageing problems occur during beer storage and can damage the beer style, especially for lager beer of a more delicate style. In this research, the impact of pasteurising intensity on beer ageing and flavour stability was studied. Through process adjustments, three types of bottled beer were obtained from one fermenter and classified by their PU values as 2 PU, 8 PU and 14 PU. The dynamic changes of related indices (taken every month) characterizing the ageing and flavour of the beer under different pasteurising intensities were investigated during a 6‐month room temperature storage period. The key factors of colour, the thiobarbituric acid (TBA) index, 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) radical scavenging activity, bitterness and total polyphenol composition, the concentration of beer volatile compounds (BVCs), and 5‐hydroxymethyl furfural (5‐HMF) were examined. Statistically, the 14 PU sample showed the highest degree of damage, with the greatest flavour change compared to the other samples.     

INFLUENCE OF pH ON FLAVOUR STALING DURING BEER STORAGE

A decreasing pH accelerated an increase in the chemiluminescence production and degradation of isohumulones and procyanidins during the storage of beer and using a model system. The sensory test showed that the addition of HCI to fresh beer accelerated the flavour staling during beer storage but that the addition of HCI to stored beer did not significantly accelerate the flavour staling. Therefore, it was thought that the acceleration of beer flavour staling is not dependent on a decrease in pH such that the decreasing pH isolates stale flavour aldehydes by a dissociation from staling-flavour aldehyde adducts but based on the fact that the decreasing pH accelerates the flavour staling reactions, free radical reactions, during beer storage.     

THE INFLUENCE OF FREE ALPHA-AMINO NITROGEN IN SORGHUM BEER FERMENTATIONS

The interactions of wort free α-amino nitrogen (FAN) and sugar in sorghum beer fermentations were quantified and a simple equation derived. This equation describes the wort FAN demand as a function of the sugar concentration necessary to produce a fully fermented beer within 48 hours. The influence of wort FAN on sorghum beer fermentations had not been quantified so research was undertaken to define sorghum beer yeasts' requirement for wort FAN and the interactions that occur between wort FAN and sugar. Laboratory, sorghum malt and adjunct, worts mashed to cover a wide range of FAN and wort sugar concentrations, were fermented and analysed. The initial wort FAN affects the ethanol production rate, FAN uptake and sugar utilisation rates.     

High Pressure Inactivation of Lactobacillus plantarum in a Model Beer System

ABSTRACT: The effects of hop extract and ethanol on growth, high pressure inactivation, and survival of Lactobacillus plantarum were determined in model beer. Corresponding to the beer spoiling ability of this strain, levels of hops and ethanol typical for beer did not inhibit growth. Pressure death time curves determined at 300 MPa were described by an empirical model taking into account the sigmoid shape of survivor curves, sublethal injury, and the presence of baroresistant cells. Ethanol (5 and 10%) enhanced pressure effects on L. plantarum whereas hop extract (50 and 100 ppm) was less effective. In contrast, hop extracts killed pressurized cells during subsequent storage in beer but ethanol did not.     

THE ROLE OF ACTIVE AND INACTIVATED PAPAIN IN BEER CHILLPROOFING

The mechanism of chillproofing of beer by papain has been studied in a series of three experiments. Changes in the molecular size of proteins and polypeptides have been monitored by chromatographic profiles on Sephadex G-25 columns. Simultaneously the production of free amino acids and changes in the colloidal stability of the beer were determined. The addition of active papain to beer affected all three parameters. By contrast when inactivated papain was added to beer neither the chromatographic profile nor the concentration of free amino acids were altered but an increase in colloidal stability occurred. The removal of active papain from beer did not affect its colloidal stability but the removal of inactivated papain from beer stabilised with this agent eliminated the chillproofing effect.     

Measurement of Human Brain Activity Evoked by Stimulation of Beer Bitterness Using Magnetoencephalography

ABSTRACT: We tried to detect the human brain activity evoked by beer taste using magnetoencephalography Subjects did not perceive bitterness and tactile stimulus differences between water and commercial beer, through a small hole of the taste stimulator, but they perceived bitterness for the beer enriched with isohumulones. The increase in the magnetic fields after the stimulation onset was observed for the stimulus of the beer with addition of isohumulones but was not observed for the stimulus of water or commercial beer, supporting the subject's comments. In 76.2% of the all measurements for the beer enriched with isohumulones, the equivalent current dipoles, placed on a subject's 3-dimensional magnetic resonance imaging, were located at the transition between the parietal operculum and the insular cortex with latency at 326.7 ± 115.5 ms. These results indicated that the brain activity stimulated by beer bitterness could be detected.     

The use of Oxygen 18 in appraising the impact of oxidation process during beer storage

To appraise the incidence of oxygen in bottled beer, the stable nonradioactive oxygen isotope 18O₂ was injected into the headspace just before ageing and subsequently analysed by proton bombardment and isotopic mass spectroscopy of all the most interesting beer fractions. Although oxygen did cause considerable oxidation of sulphites, polyphenols, and isohumulones, it was not incorporated into the carbonyl fraction, indicating that the cardboard flavour in beer is not due to lipid oxidation but to wort preparation. Nonenal potential measurement was found to be a good indicator of beer flavour staling. The impact of beer stabilisation treatments (addition of polyvinyl pyrolidone powder, potassium metabisulphite, ascorbic acid) was also investigated.     

Simulation of vacuum distillation to produce alcohol-free beer

Several processes have been developed for producing alcohol-free beer while maintaining desirable sensory characteristics. One of the most popular thermal processes used is distillation, where not only ethanol but volatile aromatic components are partly or completely removed from the beer. Based on data from the literature and using the Aspen Plus simulator, this study evaluates and compares the aroma profiles of alcohol-free beers obtained by continuous vacuum distillation with different pressures and processes. Three processes were simulated at pressures of 60, 102, and 200 mbar. The first (Process A) was a standard continuous vacuum distillation, where the bottom product was an alcohol-free beer. In the second (Process B), the bottom product was blended with a standard beer that had not undergone any thermal process. In the third (Process C), part of the top stream was mixed with the bottom product. This study considered eight major compounds in beer: ethanol, propanol, isobutanol, 2-methyl-1-butanol, 3-methyl-1-butanol, ethyl acetate, diacetyl and isoamyl acetate. The three simulated pressure ranges showed similar results, indicating that reducing the pressure below 200 mbar did not improve separation. Further, vacuum distillation did not remove diacetyl from the beer. Processes B and C resulted in beer that was richer in flavour compounds. Furthermore, when these processes were compared to Process A, the concentration of esters was markedly higher. © 2019 The Institute of Brewing & Distilling     

LAGER-TYPE BEER MADE FROM EXTRUDED MALT; SENSORY AND CHEMICAL ANALYSES

A lager-type beer was brewed from a mixture of partially dried green malt and extruded green malt (9:1). Small flavour differences were observed in the beer made from the extruded malt when compared with two other types of beer, namely standard lager and beer made from 100% green malt which was partially dried. More than 90 flavour components were described upon sniffing of the GC eluate. Most of them were present in trace amounts which did not allow their identity to be established. However, in all beer samples several unidentified components were described as giving a “roasted”, “burnt”, “bread crust” or “biscuit” odour. These odour characteristics probably derive from the alkylpyrazines present. Positively identified pyrazines were only found in the “extruded” beer, namely methylpyrazine and 2,5 (and/or-2,6)-dimethylpyrazine. However, when the beer was tasted, no characteristics associated with a roasted or burnt flavour were registered. Among the identified flavour components esters and alcohols were abundantly represented.