反吹-气相色谱法快速检测啤酒中的主要风味物质

采用反吹技术改进了气相色谱检测啤酒中乙醛、高级醇、高级酯等10种主要风味物质的方法。用配备毛细管色谱柱、氢火焰离子化检测器及微板流控装置的气相色谱仪,对啤酒直接进样,建立了一种快速分析的气相色谱分析方法。结果表明,采用内标法定量,啤酒中10种主要的风味物质具有良好的线性关系（R2＞0.999）。对同一啤酒五次进样,测得的相对标准偏差为0.13%～2.77%。对啤酒加标回收,回收率达到96%～104%。采用反吹技术可以省去复杂的样品前处理,有效降低样品基质的影响,缩短样品的分析时间,提高效率,减少材料消耗。该方法以期能快速检测生产过程中啤酒的风味物质含量,有针对性控制啤酒的生产工艺,提高啤酒的质量。     

Improvement of beer flavour with extruded rice as adjunct

Extruded rice used as adjunct for beer fermentation was prepared using a single‐screw extruder. Extrusion pretreatment facilitated the saccharification and gelatinization of the rice starch as well as the formation of a glassy cellular structure, which was evaluated through scanning electron microscopy analysis. The effects of different parameters, including barrel temperature, water content, nozzle diameter and screw speed, as well as their interactions with rice expansion rate, were evaluated by response surface methodology to determine the optimum extrusion conditions. Extruded rice was acquired using the optimum extrusion parameters (water content, barrel temperature, screw speed and nozzle diameter of 22.4%, 103°C, 8 mm and 191.6 rpm, respectively), and the expansion rate reached 275.1%. The effect of the extruded rice adjunct on beer flavour compounds was investigated by comparing flavour compounds with those of traditional rice‐adjunct beer through sensitive static headspace–capillary gas chromatography spectrometry. The contents of esters, a highly important flavour group, in extruded‐rice‐adjunct beer (ethyl acetate, isoamyl acetate, ethyl hexanoate and ethyl caprylate at 11.6, 2.4, 0.2 and 0.3 mg L⁻¹, respectively) were higher than those of the traditional rice‐adjunct beer. The contents of high alcohols were lower in the traditional rice‐adjunct beer than those in the extruded‐rice‐adjunct beer, but both levels satisfied the national standard for beer. Gas chromatography–mass spectrometry was employed to identify the flavour compounds of both beer samples through headspace–solid‐phase microextraction. Copyright © 2017 The Institute of Brewing & Distilling     

气相色谱法在啤酒分析中的应用

采用气相色谱法可对啤酒中的高级醇、酯类、羰基化合物及含硫化合物等挥发性物质进行检测,既可研究啤酒的感官品质,也可用于指导生产,优化啤酒工艺。应用气相色谱法对啤酒中挥发性物质检测的前处理方法主要有顶空进样、蒸馏、有机溶剂萃取3种。针对啤酒酒中不同的挥发性物质可选择PEG柱和氢火焰离子化检测器（FID）法进行检测;还可用内标法和外标法对啤酒中的不挥发组分进行定量检测分析。（孙悟）     

毛细管柱顶空气相色谱/质谱法分析奶啤中的风味组分

采用毛细管柱顶空气相色谱/质谱法分析奶啤中的风味组分,共检测出20种主要风味成分,它们分别属于酯类、醇类、醛类化合物。此方法操作简便、快速,为研究工作者提供了一种检验产品风味的有效手段。     

Technical Note — Analysis of Beer Aroma Compounds by Solid‐phase Microcolumn Extraction

Due to their low dead volumes, microcolumns with Tenax TA coupled to a capillary column in the modified GC inlet allow analysis of a broad range of compounds (from acetaldehyde to 2‐phenylethanol) in a single sample run. In this study, a micro‐column was filled with 10 mg of Tenax TA. Chromatograms showed well‐resolved peaks even at the beginning of the run. Static headspace was used to pre‐concentrate the compounds. The method is rapid, simple and inexpensive.     

顶空进样-毛细管气相色谱法测定啤酒的香味组分

研究了采用毛细管气相色谱分析测定啤酒中香味组分的方法。以高纯氮气作为载气 ,结合自动顶空进样技术 ,可以对啤酒中 12种主要挥发性香味组分进行定性和定量分析 ,此方法具有良好的重现性     

Analysis of flavour compounds in beer with extruded corn starch as an adjunct

Extruded corn starch (ECS) was used as an adjunct during beer fermentation and the fermentable sugars in the wort made with ECS and cooked corn starch (CCS) were determined using high‐performance liquid chromatography. The flavour compounds of beer made using ECS and CCS were determined using headspace solid‐phase micro‐extraction gas chromatography–mass spectrometry, and eight volatile compounds in ECS and CCS beer were quantified using gas chromatography (GC). Five fermentable sugars (fructose, glucose, sucrose, maltose, maltotriose) were detected in both samples, and their content in ECS wort was higher than in CCS wort, except for maltose. Seventy‐three flavour compounds were identified and quantified in ECS beer, while 58 compounds were determined in CCS beer. Both ECS and CCS can be used to produce beer; however, the concentration of characteristic beer flavour compounds in ECS beer was higher than in CCS beer. Copyright © 2018 The Institute of Brewing & Distilling     

Analysis of flavour compounds in beer with extruded sorghum as an adjunct using headspace solid‐phase micro‐extraction and gas chromatography–mass spectrometry

Sorghum is a widely used adjunct that is used in the production of beer and increasingly affects beer flavour as the amount added increases. The aim of this work was to establish a simple, solvent‐free technique, without derivatization, to analyse flavours and typical volatile compounds present in extruded and unextruded sorghum beer, and to compare the flavour differences of the two types of beer. Headspace solid‐phase micro‐extraction gas chromatography–mass spectrometry was used to determine the flavours in the two beers and eight typical volatile compounds were quantified using GC. Forty‐five flavour compounds were identified and quantified in extruded white sorghum beer, while 31 flavour compounds were identified in unextruded white sorghum beer. Extruded or unextruded white sorghum can be used to produce ale beer, but the primary flavour content in the extruded white sorghum beer was higher than in the unextruded white sorghum beer. Copyright © 2016 The Institute of Brewing & Distilling     

GC-MS法分析西瓜精酿啤酒中的风味物质

为了研究分析西瓜精酿啤酒中的风味物质,采用静态-顶空固相微萃取（HS-SPME）结合气相色谱-质谱（GC-MS）联用的方法,对西瓜精酿啤酒及普通精酿啤酒中的风味物质进行了对比分析。结果表明,从西瓜精酿啤酒中共分离出48种物质,确定了其中的36种物质;从普通精酿啤酒中共分离出42种物质,确定了其中的41种物质。与普通精酿啤酒确定风味成分相比,己酸乙酯、癸醛、可卡醛、壬酸乙酯、癸酸乙酯等11种物质仅在西瓜精酿啤酒中检出,这些成分赋予了西瓜精酿啤酒独有风味。     

A CHEAP,DIRECT METHOD FOR THE ESTIMATION OF DISSOLVED AIR IN BEER

A plastic medical syringe is used to collect a beer sample and to apply vacuum to de-gas it. The beer is then replaced with sodium hydroxide solution and alkali-insoluble gas is displaced into a calibrated plastic capillary tube. Dissolved-air contents in the range 2 ml/litre to 50 ml/litre have been estimated with a repeatability adequate for many process investigations.     

Effect of oak wood on the quality of beer

Maturation in wood is an important practice that is widely used in the production of high‐quality beverages. The effect of French oak cubes on young lager beer was studied. Oak cubes (with light, medium or heavy toasting) were added to the beer, which was stored at 0°C for 3 months. Beer samples were analysed monthly, and an acceptance test was performed at the end of 3 months. The content of volatile compounds (aldehydes, esters and higher alcohols) was determined by gas chromatography using a flame ionization detector, and the content of low molecular weight phenolic compounds was determined by high‐performance liquid chromatography. The contents of aldehydes, esters, higher alcohols and wood‐derived compounds increased during the 3‐month maturation period. Lager beer stored with heavily toasted oak cubes had the highest concentration of low‐molecular‐weight phenolic compounds, followed by the beer matured in an oak barrel. These results suggest that beer maturation in wood barrels or with oak cubes changed the composition of their oak‐related aromatic compounds, indicating that interactions between the beer and the wood occurred. Copyright © 2015 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     

VOLATILE BASIC COMPOUNDS DERIVED FROM ROASTED BARLEY

By gas chromatography/mass spectrometry twenty-three basic heterocyclic compounds have been identified in an extract from roasted barley. Several other such compounds have been identified tentatively. The classes of compounds include pyridines, pyrazines, thiazoles and oxazoles. Such compounds appear to contribute to the flavour of beer brewed with grists containing roasted barley.     

静态顶空进样分析啤酒的挥发性风味物质

用标准曲线代替传统的校正因子，以内标法作定量分析，采用静态顶空法的气相色谱分析技术对啤酒中的五种风味物质进行定量测定，取得明确的结果，为啤酒生产中的质量控制提供了数据说明。     

DETERMINATION OF THE FILTERABILITY OF BEER

A method for the determination of the filterability of beer has been evaluated by members of the European Brewery Convention Analysis Committee. The method is based on the filtration of a beer sample, with a standard amount of diatomaceous earth (DE), under standardised conditions. Repeatability of the test was quite good, however the predictive value of the test is still questionable since no direct correlation could be established between the different filtercake values and industrial filtration problems. No collaborative test was performed as the filterability has to be determined on unfiltered beer; the test is easy to run, and as for the other filterability tests, day to day practice in a brewery will reveal its usefulness.     

啤酒中挥发性风味物质的分析及风味评价

应用气相色谱定量分析啤酒中的挥发性风味物质如醇类,酯类,连二酮,含硫化合物等,通过风味强度进行风味特征评价及风味差别度的判别,达到控制质量的目的,结合应用GC－MS,气相色谱－气味测定法（GCO）,电子自旋共振（ESR）等技术对啤酒,酿造过程及原料中的风味化合物和异味组分进行测定的探讨。     

Part III: the influence of serial repitching of Saccharomyces pastorianus on the production dynamics of some important aroma compounds during the fermentation of barley and gluten‐free buckwheat and quinoa wort

The present paper is the last report of a comprehensive study regarding the influence of the serial repitching of Saccharomyces pastorianus TUM 34/70 on the composition of a barley, buckwheat or quinoa fermentation medium. In particular, it focuses on the production dynamics of important volatile compounds typically associated with the aroma of beer. Samples were taken every 24 h after 11 serial repitchings of a single starter culture, analysed for the particular aroma compound content by distillation followed by gas chromatography with flame ionization detection. The term ‘serial repitching factor’ is used for the first time to support the visual evaluation of the influence of serial repitching. Results showed that the levels of methanol in the quinoa wort fermentation were only slightly higher than in barley and in practical terms independent of successive fermentation. The behaviour of acetaldehyde in quinoa was similar to that in barley. However, there was a final 2‐fold lower production of some important aroma compounds compared with barley and buckwheat and for this reason quinoa cannot be recommended as a gluten‐free substitute to produce a bottom‐fermented beer. Regarding the buckwheat wort fermentation, a 2‐ to 3‐times lower final acetaldehyde content than in barley is desirable, whereas a relatively high methanol content is not desirable. Barley and buckwheat showed comparable sum concentrations and similar overall profiles of some important aroma compounds. From this perspective, buckwheat appears to be a promising substitute for barley as a brewing raw material. The overall conclusions of our comprehensive study (Parts I–III) are that buckwheat shows adequate brewing properties to substitute for barley in the commercial preparation of a bottom‐fermented gluten‐free beer‐like beverage, and yeast can be repitched at least 11 times. In contrast, quinoa in practical terms shows no substitutional potential for barley in beer; however, it has many nutritious advantages, thus the commercial preparation of a unique, bottom‐fermented gluten‐free ‘non‐beer‐like’ beverage – where the yeast could be repitched six times at most – appears feasible. Copyright © 2015 The Institute of Brewing & Distilling     

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.     

Determination of flavour compounds in beer using stir‐bar sorptive extraction and solid‐phase microextraction

The analysis of volatile compounds in beer is important for quality control in the brewing industry. In this study, stir‐bar sorptive extraction (SBSE) and solid‐phase microextraction (SPME), two solvent‐less enrichment techniques, were applied in combination with gas chromatography flame ionization detection (GC/FID) for the determination of four flavour compounds (isoamyl acetate, ethyl hexanoate, benzaldehyde, myrcene) in beer. Limits of detection, linearity and repeatability of both methods were determined using standard ethanol solutions, while accuracy was determined by conducting recovery tests on commercial beer samples. Both methods were characterized by high linearity (r > 0.996) and repeatability (RSD = 1.76–10.66%). When both methods were compared, higher recoveries were obtained by SBSE, with limits of detection 1.8–2.8 times lower compared with SPME. In the analysis of commercial beer samples using both methods, SBSE analysis resulted in higher recoveries, therefore demonstrating promise for the analysis of beer volatiles. Copyright © 2015 The Institute of Brewing & Distilling