THE USE OF CONTROLLED LEVELS OF ACTIDIONE FOR BREWING AND NON-BREWING YEAST STRAIN DIFFERENTIATION

The variability of results using actidione media for the identification of beer spoilage bacteria has been shown to be due to the heat sensitivity of this reagent. Critical evaluation shows that with a particular brewery yeast, media containing 0·06 p.p.m. allow the growth of a single brewing strain but inhibit others. This permits the rapid classification of yeast strains in this pitching yeast. In a further brewery, media containing 0·16 p.p.m. differentiate brewing yeast strains from beer spoilage yeasts and this permits the quantitative assessment of these for process control at all stages of brewing. In a particular instance where a culture yeast strain is not inhibited at 0·16 p.p.m. but is p-aminobenzoic acid dependent, a differential medium incorporating this low level of actidione and omitting the vitamin allows the identification of beer spoilage yeasts in process control. These results illustrate the potential of this approach for microbiological control in specific brewery problems.     

THE INFLUENCE OF 2-ACETOHYDROXY ACIDS ON THE DETERMINATION OF VICINAL DIKETONES IN BEER AND DURING FERMENTATION

During sampling and determination of diacetyl, 2-acetohydroxy acids are easily converted to vicinal diketones. A simple procedure for gas chromatographic determination of diacetyl, 2-acetolactate, acetoin and the homologous compounds is given. By careful sampling, less than 0·01 ppm of diacetyl was detected during the main fermentation in one brewery, whereas another strain of brewer's yeast yielded a maximum of 1·7 ppm of diacetyl. When samples of fermenting liquids are exposed to air at 60°C, complete conversion of 2-acetohydroxy acids takes place in less than one hour. The possibility that part of 2-acetolactate may be converted to acetoin, however, cannot be excluded. In finished beer 2-acetolactate levels of 0·2–0·5 ppm were observed. During the main fermentation the values ranged from 0·5–2·5 ppm.     

LIPIDS IN THE BREWERY—A MATERIAL BALANCE

Lipids, measured as total long-chain fatty acids, have been determined on samples taken from all stages in a pilot-scale brewery. This exercise has identified both the materials which supply the lipids in brewing, and the processes responsible for their removal. The balance demonstrates areas where significant quantities of lipid are generated or lost. Very little of the lipid present in the raw materials survives the brewing process: of the 277 g lipid in 8800 g malt, only 0·1 g (0·03%) remains in the finished beer. Spent grains, hot break and cropped yeast are all effective means of removing lipids.     

FLUOROMETRIC DETERMINATION OF CYSTEINE IN BEER BY HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY WITH PRECOLUMN DERIVATISATION

A high-performance liquid chromatographic procedure (HPLC) is described for the fluorometric determination of cysteine (CySH) in beer. Reduced CySH in beer is reacted with a fluorescent reagent, N-(9-acridinyl) maleimide (NAM), at pH 8·8 for 15 h to form a stable fluorescent derivative. The resulting reaction mixture is analysed by reversed-phase gradient elution HPLC. Under the optimised conditions for chromatography, ca 0·1 mg of CySH per litre of beer can be determined. Total CySH is determined by electrolytic reduction at a Hg pool electrode prior to the HPLC analysis. The levels of reduced and total CySH in 28 brands of commercial lager beers ranged from 0·2 to 0·9 mg/litre, and from 2·1 to 13·5 mg/litre, respectively.     

Effect of high hydrostatic pressure on quality parameters of lager beer

Unpasteurized lager beer samples from a commercial brewery were treated either by high hydrostatic pressure (HHP; 200, 250, 300, 350 MPa for 3 and 5 min at 20 °C) or by conventional heat pasteurization (60 °C for 15 min). The main attributes of the beer, such as ethanol content, extract and pH, were not affected by either treatment; however HHP and heat pasteurization affected colour, chill haze, protein sensitivity and bitterness. Change in bitterness was higher in conventional heat pasteurization, but pressures up to 300 MPa had no significant affect on bitterness. Although more studies should be carried out to investigate the effects of HHP treatment on different types of lagers and ales, our results revealed that HHP could be successfully used to process beer, even at temperatures well below those required for heat pasteurization, without affecting some of the quality attributes. Copyright © 2005 Society of Chemical Industry     

Effects of β‐Glucan,Shearing and Environmental Factors on the Turbidity of Wort and Beer

The presence of added β‐glucan in wort caused increased turbidity levels, which increased at higher molecular weights and concentrations of the polymer. Levels of pH, maltose and ethanol, and shear experienced in a brewery also influenced the turbidity of wort and beer. Haze levels of beer after 0.45 μm membrane filtration were found to decrease due to the removal of non‐β‐glucan particles. Cold storage at 4°C for two weeks was found not to lower the turbidity caused by high concentrations of high molecular weight β‐glucan polymers.     

Group-specific PCR-RFLP and real-time PCR methods for detection and tentative discrimination of strictly anaerobic beer-spoilage bacteria of the class Clostridia

The strictly anaerobic brewery contaminants of the genera Pectinatus, Megasphaera, Selenomonas and Zymophilus in the class Clostridia constitute an important group of spoilage bacteria of unpasteurised, packaged beers. The aim of this study was to develop and evaluate group-specific PCR methods to detect and differentiate these bacteria in beer. A group-specific primer pair targeting a 342-bp variable region of the 16S rRNA gene was designed and evaluated in end-point PCR with gel electrophoresis and in real-time PCR with SYBR Green I dye. Significant cross-reactions with DNAs from any of the forty-two brewery-related, non-target microbes or from real brewery samples were not detected in either PCR system. The group-specific end-point and real-time PCR products could be differentiated according to species/genus and spoilage potential using restriction fragment length polymorphism (KpnI, XmnI, BssHII, ScaI) and melting point curve analysis, respectively. In combination with a rapid DNA extraction method, the PCR reactions detected ca 10(0)-10(3) CFU per 25 ml of beer depending on the strain and on the PCR system. The end-point and real-time PCR analysis took 6-7 h and 2-3 h, respectively. Pre-PCR enrichment of beer samples for 1-3 days ensured the detection of even a single cultivable cell. The PCR and cultivation results of real brewery samples were mostly congruent but the PCR methods were occasionally more sensitive. The PCR methods developed allow the detection of all the nine beer-spoilage Pectinatus, Megasphaera, Selenomonas and Zymophilus species in a single reaction and their differentiation below group level and reduce the analysis time for testing of their presence in beer samples by 1-2 days. The methods can be applied for brewery routine quality control and for studying occurrence, diversity and numbers of the strictly anaerobic beer spoilers in the brewing process.     

DETECTION AND IDENTIFICATION OF LACTOBACILLUS LINDNERI FROM BREWERY ENVIRONMENTS

Ten detection media and six cultivation techniques were evaluated for the detection of a harmful brewery contaminant, for which the name Lactobacillus lindneri was recently revived. These bacteria showed slow and weak growth on solid media. However, enrichment of beer with NBB-C or the use of a mixture of MRS and beer (4:1 v/v) reduced the detection time by 2 days or more, depending on the strain, compared to cultivation on solid brewery media. Eight brewery isolates from different origins, the type strain and a test strain were characterized by carbohydrate fermentation tests (API 50 CHL), by a chemotaxonomical (SDS-PAGE) and by a genomic fingerprinting (ribotyping) method. The results obtained by all these methods indicated that the isolates studied form a single group and can be assigned to the species L. lindneri. However, using the current standard reagents, ribotyping cannot discriminate the strains isolated from different sources .     

The Occurrence of Beer Spoilage Lactic Acid Bacteria in Craft Beer Production

Beer is one of the world's most ancient and widely consumed fermented alcoholic beverages produced with water, malted cereal grains (generally barley and wheat), hops, and yeast. Beer is considered an unfavorable substrate of growth for many microorganisms, however, there are a limited number of bacteria and yeasts, which are capable of growth and may spoil beer especially if it is not pasteurized or sterile‐filtered as craft beer. The aim of this research study was to track beer spoilage lactic acid bacteria (LAB) inside a brewery and during the craft beer production process. To that end, indoor air and work surface samples, collected in the brewery under study, together with commercial active dry yeasts, exhausted yeasts, yeast pellet (obtained after mature beer centrifugation), and spoiled beers were analyzed through culture‐dependent methods and PCR‐DGGE in order to identify the contaminant LAB species and the source of contamination. Lactobacillus brevis was detected in a spoiled beer and in a commercial active dry yeast. Other LAB species and bacteria ascribed to Staphylococcus sp., Enterobaceriaceae, and Acetobacter sp. were found in the brewery. In conclusion, the PCR‐DGGE technique coupled with the culture‐dependent method was found to be a useful tool for identifying the beer spoilage bacteria and the source of contamination. The analyses carried out on raw materials, by‐products, final products, and the brewery were useful for implementing a sanitization plan to be adopted in the production plant.     

THE RELATIONSHIP OF DIMETHYL SULPHIDE LEVELS IN MALT,WORT AND BEER

The half-life for the conversion of malt dimethyl sulphide (DMS) precursor to free DMS has been determined at various temperatures and pH values. At pH 5·2 the half-life of the precursor in wort (S.G. 1·060) at its boiling point is 38 min, and is doubled for each 6°C fall in temperature. At pH 5·5 the half-life at the boiling point is 32·5 min. Knowing the stability of the precursor at the various temperatures in the brewing process, the extent of conversion to free DMS in wort at pitching can be predicted for malt of a given precursor content and for a given set of process conditions. The results of DMS analyses of samples taken during brewery trials are in reasonable agreement with the predicted values. This work involved infusion mashing only, but the same principles apply to decoction mashing. The fate of precursor and free DMS during fermentation and conditioning has been followed on a production scale. With some brews, where high levels of free DMS were present at pitching, much free DMS was lost during fermentation. Also, precursor DMS reappeared in the beer after a few days and there was some increase in the level of free DMS. The DMS precursor in green malt has been isolated by ion-exchange and gel-filtration chromatography. A preparation has been obtained which has 0·6 mol potential DMS per mol amino nitrogen. Thin layer chromatography showed that the preparation and its hydrolysis product had the same R_f values as S-methylmethionine and homoserine respectively.     

High Gravity Brewing by Continuous Process Using Immobilised Yeast: Effect of Wort Original Gravity on Fermentation Performance

The present work evaluated the influence of all‐malt wort original gravity on fermentative parameters and flavour‐active compound formation during primary fermentation of high gravity brewing by a continuous process using a lager yeast immobilised on a natural carrier obtained from brewer's spent grain (the main brewery by‐product). The all‐malt worts with original gravity (OG) ranging from 13.4 to 18.5°Plato were prepared by diluting a very‐high‐gravity wort (20°Plato) with sterile brewery water. The continuous assay was carried out in a bubble column bioreactor with a total working volume of 5.2 litres, at 15°C, using a constant gas flow rate of 250 mL/min (200 mL/min of CO₂ and 50 mL/min of air) and a dilution rate of 0.04 h^?1 (residence time of 25 h). The results indicated that as the wort OG was increased, the ethanol concentration of the outflowing beer increased. On the other hand, the continuous fermentation of the most concentrated worts (16.6 and 18.5°Plato) resulted in beers with unbalanced flavour profiles due to excessive ethyl acetate formation. The immobilised cell concentration appeared to be nearly independent from increasing wort OG.     

啤酒酵母的综合利用

论述了啤酒厂废弃酵母的开发利用,针对啤酒工业中利用啤酒酵母开发高附加值产品进行综述。     

GAS CHROMATOGRAPHIC DETERMINATION OF TYROSOL AND TRYPTOPHOL IN WINES AND BEERS

A gas chromatographic method for the determination of tyrosol and tryptophol in wines and beers has been developed. The aromatic fusel alcohols are extracted with ether or ethyl acetate from a sample made alkaline with Na₂CO₃ and saturated with NaCl. In beer determinations the extraction is performed with ethyl acetate in order to avoid complications caused by emulsion. Most of the solvent is removed by distillation and the rest is cautiously allowed to evaporate. The gas chromatographic determination of tyrosol and tryptophol is performed in a 0·5-m. Apiezon M-DEGS column at 190°C. According to the infra-red spectra, both components are eluted without being decomposed at this temperature. In the grape wines investigated, tyrosol was found in amounts of 10–40 mg. per litre, in two Finnish berry wines 10–15 mg. per litre and in two different types of pale lager beers 5–10 mg. per litre. The same samples contained about 1–4 mg. tryptophol per litre. The two white grape wines and one red berry wine were exceptional, with only 0·2–0·3 mg. tryptophol per litre.     

A study of beer bitterness loss during the various stages of the Romanian beer production process

Beer is one of the oldest known alcoholic beverages produced by a yeast fermentation of a cereal extract that was germinated in water beforehand. The bitter taste of beer comes from the group of substances introduced during wort boiling, which are the extracted components of hops. The aim of this study was to determine some characteristics of beer (original extract, alcohol content, colour, pH, total acidity, carbon dioxide and bitterness values) during the three stages of the beer production process in a typical Romanian brewery. Measurements were carried out on 60 samples of beers, 10 measurements for each step of the process examining wort, unfiltered fermented beer and bottled beer (final product) from two different types of beer (light and dark). Statistical process control of the beer was performed. Losses in the bitterness units during the production process were between 24.7 and 41.54%, reported in terms of final product. Copyright © 2013 The Institute of Brewing & Distilling     

THE ISOELECTRIC FOCUSING OF BEER PROTEINS IN POLYACRYLAMIDE GEL

A technique has been developed for fractionating beer proteins by isoelectric focusing in polyacrylamide gel which enables protein species with isoelectric points differing by as little as 0·1 pH unit to be separated as clearly defined bands. The isoelectric profile of an all-malt beer was found to be similar to that of the parent wort but significant changes occurred when a beer was stabilized in the laboratory by three different treatments.     

西瓜啤酒制作工艺的研究

以西瓜汁和大麦芽为主要原料,采用啤酒独特的低温发酵工艺酿制西瓜啤酒。通过单因素试验和响应面分析试验,以感官评分为评价标准,结合理化指标研究了西瓜汁添加量、西瓜汁添加时间和原麦汁浓度对西瓜啤酒品质的影响。确定了西瓜啤酒的最佳发酵工艺条件为：西瓜汁添加量14.0%,在发酵的第4.5天添加西瓜汁,原麦汁浓度11.2°P。在此条件下,进行了400 L发酵罐的验证试验,获得了一种具有西瓜清爽口感和啤酒典型口感的西瓜果味啤酒。     

AMINO ACID ANALYSIS OF BEER POLYPEPTIDES

The principles of amino acid analysis of proteins and polypeptides are reviewed. Analysis of the amino acid composition of dialysed beer material prepared from a wide variety of commercial and pilot brewery beers showed that the principal amino acids comprised glutamic acid/glutamine, proline, glycine and aspartic acid/asparagine. The results from the analysis of a series of pilot brewery beers brewed under standardised conditions showed that the composition of the grist may influence the amino acid composition of beer polypeptide fractions. Dialysed beer material prepared from beer brewed from grists containing torrified wheat, wheat flour and malted wheat contained greater proportions of glutamic acid/glutamine compared to material prepared from all malt beers. Further fractionation and analysis of dialysed beer material prepared from pilot brewery beers suggested that fractions MW>60000 contained polypeptide material derived from yeast mannan-protein. In addition fractions MW>60000 prepared from beer brewed from grists containing torrified wheat, wheat flour or all malted wheat may contain high molecular weight polypeptide material derived from wheat proteins. The results from the analysis of fraction MW 40,000–60000 prepared from beers brewed from grists containing all malt, 80% malt and 20% torrified wheat and 50% malt and 50% malted wheat are consistent with the presence of polypeptide material derived from cereal albumins and globulins whereas fractions MW 40,000–60000 prepared from beers brewed from 80% malt and 20% wheat flour and 100% malted wheat may contain polypeptide material derived from wheat prolamins and glutelins. The amino acid composition of fraction MW 20,000–40,000 from all pilot brewery beers investigated is consistent with the presence of polypeptide material derived from cereal prolamins and glutelins. The amino acid composition of beer polypeptide fractions may be used to detect the use of wheat adjuncts in beer brewing.     

IDENTIFICATION OF A GROWTH FACTOR IN TOMATO JUICE FOR A NEWLY ISOLATED STRAIN OF PEDIOCOCCUS CEREVISIAE

A newly isolated strain (L-73) of Pediococcus cerevisiae showed very slow growth in the Nakagawa medium which has been routinely used for the detection of lactic acid bacteria in the brewery. When the Nakagawa medium was enriched with 2% tomato juice extract or when the medium was prepared with the use of unhopped beer, strain L-73 showed good growth. The growth-stimulating factor in tomato juice was purified by chromatography on a charcoal column and it was finally identified by bio-autography as 4′-0-(β-D-glucopyranosyl)-D-pantothenic acid.     

THE QUANTITATIVE DETERMINATION OF GLYCEROL IN BEER BY GAS-LIQUID CHROMATOGRAPHY

The glycerol present In beer in conjunction with the constituent sugars was resolved as the trimethylsilyl derivative on a 2 ft. × 1/4 in. o.d. stainless steel column packed with 1% OV 17 on Chromosorb W-H.P., 80–100 mesh. Complete separation and quantitative estimation were obtained. Coefficients of variation for determination of glycerol in aqueous solution were found to be 2·7% for machine operation alone and 4·1% for the total procedure. For glycerol determination in the presence of beer the coefficient of variation for the total procedure was doubled. A survey of Canadian beers indicated a glycerol level of approximately 2 mg./ml. and showed no trend according to type, locality or brand. Taste test studies revealed the threshold level of glycerol detection in a test beer to be 10 mg./ml. The addition of glycerol to beer above and below the threshold level was found to modify the flavour of the product.