Showing papers in "Journal of The Institute of Brewing in 1991"

The effects of mashing temperature and mash thickness on wort carbohydrate composition

Abstract: Temperature and mash thickness are shown to affect both mash performance and enzyme activity. Alpha amylase was found to be considerably more resistant to heat inactivation than was beta amylase. This difference was reflected by changes in wort fermentability that were manifest at temperatures below those which affected levels of extract. Increasing the mashing temperature from 65°C to 80°C had only a slight effect on extract but reduced wort fermentability from over 70% to less than 30%. At 85°C and over, when temperature had a significant effect on alpha amylase, as well as on beta-amylase, extract was lost and starch was present in the wort. Diluting the mash with liquor had a similar effect to that of increasing temperature on both the amylolytic enzymes and on the mash performance. Thin mashes contained more starch and fewer fermentable sugars than did thick mashes at the same temperature. These changes can be related to the stability of the amylolytic enzymes.

Variability of essential oils of hops, humulus lupulus l.

Abstract: A standard method for distinguishing the essential oils in hops has been developed. Factor, rotation-factor analyses have been used as well as correlation between gas chromatography and organoleptic estimation of aroma. A model for distinguishing 14 groups of oils using 31 descriptors has been developed utilising the variability of components in essential oils. The results are valid for the oils from older established plants, picked at full maturity in Slovenia.

Instrumental evaluation of the mouthfeel of beer and correlation with sensory evaluation

Abstract: Physical and chemical measurements were made on a set of 30 beers which had previously been used to characterize the sensory attributes of the mouthfeel of beer using descriptive analysis techniques; these measurements were then correlated with the sensory attributes. By principal component analysis of the physical and chemical data it was found that the first principal component (PC) was a function of dissolved substances in the beer and the second PC was a function of degree of fermentation. When principal component analysis was performed on the combined sensory and instrumental data, the 30 beers displayed clustering in the PC space based on beer type.

Structure of total barley beta‐glucan1

Abstract: The fine structure of total barley β-glucan, as extracted by hot perchloric acid, was investigated by partial enzymatic hydrolysis. Molecular weight profiles of the resulting oligomeric products were similar to those from hydrolysed 40°C water-soluble β-glucan. Concentrations of individual oligosaccharides from total β-glucan were found to vary between oats and barley and among barley varieties, suggesting variability in β-glucan structure. Methylation studies, using HPLC to separate methylated sugars, showed no evidence for the presence of contiguous β-1,3 links in total barley β-glucan, although not all fractions of total β-glucan were analysed.

Induction of premature yeast flocculation by a polysaccharide fraction isolated from malt husk

Abstract: A husk polysaccharide component from a malt causing premature yeast flocculation was isolated and characterized, and its effect on the fermentation pattern of Saccharomyces cerevisiae 2036 established. A particular malt husk extract, obtained using a mild aqueous extraction procedure, induced premature flocculation when added to fermentations in normal wort. In sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) of the malt husk extract, 4 protein bands (42,600; 17,500; 15,100 and 13,100 daltons) and a high molecular weight polysaccharide were identified. These components were separated by gel chromatography and their effect on the fermentation pattern established. Only the polysaccharide fraction induced premature flocculation. Sugar analysis of this fraction indicated the presence of arabinose, galactose, glucose, mannose, xylose, rhamnose and an acidic sugar component. The polysaccharide fraction showed haemoagglutination activity, which was not inhibited by any of 11 simple sugars tested.

Identification of lambic superattenuating micro-organisms by the use of selective antibiotics

Abstract: The microbial population present in Iambic beer after one year of spontaneous fermentation consists mainly of Brettanomyces yeasts, lactic acid bacteria and acetic acid bacteria. The density of the wort by that time has decreased to around 3.5° Plato. At that time a period of superattentuation is initiated, resulting in a Iambic with sometimes less than 1° Plato. Such old Iambics are used in the production of gueuze. In order to find out which organisms are really necessary for this process. Iambic attenuated to around 3.5° Plato was pasteurized and re-inoculated with a mixed microbial population obtained from fermenting Iambic. By the addition of the antibiotics actidione, pimaricin, gentamycin, oxytetracycline and nisin it was found that Brettanomyces was the main organism responsible for superattenuation, although this was less pronounced when Pediococcus was absent. Acetic acid bacteria were not involved. Bacteria alone were not really superattenuating. The process with Iambic wort which had reached the 3.5° Plato value by a natural spontaneous fermentation was slower than with a Iambic wort pre-fermented to 3.5° Plato with S. cerevisiae. It was found that Brettanomyces but not Saccharomyces survives well under the conditions normally found for a 1 year old Iambic.

The release of yeast proteolytic enzymes into beer

Abstract: A simple assay to screen brewing yeast for the release of proteases into beer is outlined and the impact of the yeast proteases on beer foam stability is discussed.

Cloning of a yeast gene which causes phenolic off-flavours in beer

Abstract: A gene (POF1) has been cloned, which confers upon yeast (Saccharomyces cerevisiae) the ability to decarboxylate phenolic acids such as ferulic and trans-cinnamic acid. This property was previously shown to be a cause of phenolic off-flavour production in wort fermentations. The identity of the cloned gene was confirmed as POF1 by gene disruption techniques. Southern blotting of total genomic DNA revealed that sequences homologous to POF1 are conserved in Pof− brewing strains of Sacch. cerevisiae. The transformation of a Pof− lager strain with the cloned POF1 gene led to the production of an aroma characteristic of a phenolic off-flavour, when the transformed strain was used in wort fermentations. This latter observation suggests that the Pof− phenotype of brewers' yeast is specifically due to the absence of a functional POF1 gene.

Wort enterobacteria and other microbial populations involved during the first month of lambic fermentation

Abstract: Lambic is a special type of Belgian beer obtained by spontaneous fermentation. The micro-organisms occurring during the first month of lambic fermentation were counted using several selective media. During this period a mixed flora is present in which the Enterobacteriaceae predominate. They were isolated from samples of lambic of different ages originating from different breweries and identified using the minitek identification system. Much variation may occur in types of Enterobacteriaceae: Klebsiella aerogenes, Enterobacter cloacae, E. aerogenes, Escherichia coli, Citrobacter freundii, A-D group bacteria and Hafnia alvei are found during the first month of fermentation. E. cloacae is found most frequently followed by K. aerogenes. After 30 to 40 days all Enterobacteria die off because of the activities of yeasts. Lactic acid and acetic acid bacteria are found in very low numbers during the first month of fermentation; Staphylococci and Streptococci are not present.

Use of the hagberg falling number apparatus to determine malt and barley quality.

Abstract: The Hagberg Falling Number measurement, widely used in the milling industry for assessing the baking quality of wheat flour, has been modified and used as a rapid mashing technique to assess malt quality. Barley Malt flour is mixed with cold mashing liquor containing 0.1% calcium chloride and 15 mM beta-mercapto-ethanol. The slurry is heated and mixed by the Falling Number apparatus, and the starch is gelatinized. After one minute of heating/mixing the stirring rods are raised and released. As the gelatinized starch is hydrolysed by amylases, the viscosity of the slurry decreases allowing the stirring rods to fall. The time taken for these rods to fall a fixed distance is called the Falling Number. A relationship has been determined between the Falling Number obtained for a malt and the quality of the malt. Poor quality malts had a high Falling Number (e.g. >200s) whilst good malts had a low Falling Number (e.g. <150s). The correlation coefficient between Falling Number and Hot Water Extract (IOB coarse grind) was −0.89, and between Falling Number and Friability was −0.96. These good correlations indicate the measurement was influenced by the degree of endosperm modification. Being a mashing technique, however, the Falling Number was also influenced by other factors which influence mashing such as enzyme complement and water binding. This technique has the potential to measure malt quality using a commercial apparatus more rapidly than present malt analyses. No significant relationship could be determined between the Falling Number and the malting quality of barley.

A study of beer staling using chemiluninescence analysis

Abstract: 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.

Studies on the binding between yeast and a malt polysaccharide that induces heavy yeast flocculation

Abstract: A factor which causes heavy yeast flocculation of Saccharomyces cerevisiae 2036 was found to be associated with the malt husk by Axcell et al.1 In the present work it was established that the factor is a polysaccharide and immunological techniques were used to show that the factor binds to the yeast cell surface during fermentation. It was shown that the factor is present at significantly higher concentrations in wort causing premature yeast flocculation than in normal wort. A particular malt husk extract, obtained using a mild aqueous extraction procedure, induced premature flocculation when added to fermentations in normal wort. In sodium-dodecyl-sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) of the malt husk extract, 4 protein bands (42,600; 17,500, 15,100 and 13,100 daltons) and a high MW (molecular weight) polysaccharide were identified. Antibodies were raised against electroeluted proteins as well as against the homogenized polyacrylamide gel containing the polysaccharide band. Enzyme-linked immunosorbent assays (ELISA) showed that the protein components were present in similar concentrations in premature flocculent and normal wort. In contrast, the high MW polysaccharide occurred at a significantly higher concentration in wort inducing premature flocculation than in normal wort. Immunogold electron microscopy showed that the high MW polysaccharide bound extensively to the surface of flocculent cells grown in premature flocculent wort. There was markedly less labelling on yeast cells grown in normal wort. Negligible labelling occurred when the yeast cells were incubated with antibodies against the different protein components of malt husk extract.

The effect of pre-isomerised hop extract on the properties of model protein stabilized foams

Abstract: A commercial sample of pre-isomerised hop iso-alpha acids was found to increase the stability of foams stabilized by bovine serum albumin or β-lactoglobulin as determined by a conductimetric technique under a variety of solution conditions. Suspended thin films containing hop iso-alpha acids were found to have drainage kinetics and equilibrium thicknesses distinct from control samples. The surface diffusion coefficient of fluorescent-labelled β-lactoglobulin in films partially destabilized by the presence of the non-ionic detergent, Tween 20 was found to be significantly decreased by the presence of hop iso-alpha acids. These findings support the hypothesis that hop acids stabilize foams by crosslinking surface adsorbed proteins.

Growth of aerobic wild yeasts

Abstract: Wild yeasts of the genera Debaryomyces, Hansenula and Pichia are commonly considered to be associated with spoilage only under aerobic conditions. However, in pure cultures in either wort or a synthetic medium of yeast nitrogen base + 10% glucose, yeasts of these genera grew as well as a brewing strain of Saccharomyces cerevisiae under anaerobic conditions. Growth of S. cerevisiae was increased by the addition of unsaturated fatty acid (Tween 80) or ergosterol to the medium for anaerobic culture. No equivalent requirement was observed for the wild yeasts examined. Indeed, growth of the wild yeasts was often reduced by the addition of Tween 80, which as a surfactant prevented formation of the surface film of growth. Even under anaerobic conditions, these yeasts grew best with a surface pellicle. Although capable of good anaerobic growth in pure culture, growth of the wild yeasts was suppressed under anaerobic conditions in mixed culture with S. cerevisiae, simulating a contaminated brewery fermentation. However, the contaminants competed successfully with S. cerevisiae under aerobic conditions. There was no evidence of a “killer” effect, but prevention of pellicle formation, or production of inhibitory levels of pH or ethanol under anaerobic conditions could explain the suppression of wild yeasts under anaerobic fermentation conditions.

Fast isomerisation of humulone by photo‐reaction: preparation of an hplc standard

Abstract: A rapid photo-isomerisation method is described for the production of photo-isohumulone. The use of photo-isohumulone as an ultra-pure standard for the HPLC analysis of iso-alpha acids is described.

Contamination of immobilized yeast bioreactors

Abstract: Microbiological contamination of immobilized yeast bioreactors for lagering of beer was studied. Four common brewery contaminants and two contaminants isolated from the continuous processing system were tested for their ability to survive and grow in the packed bed DEAE-cellulose bioreactors. Bacterial contaminants were washed out within less than six weeks without causing any alterations in the flavour composition of the beer. The initial contamination levels were 104–106 cells ml−1. Gram positive lactic acid bacteria, Lactobacillus brevis and Pediococcus damnosus, were more persistent than a Gram negative wort bacterium, Enterobacter agglomerans. The wild yeasts Saccharomyces cerevisiae (ex. diastaticus) and Candida krusei were the most persistent contaminants and the only ones able to grow in the reactors. Another wild yeast, Rhodotorula rubra, did not survive in competition with brewer's yeast and was washed out within a few weeks. C. krusei and R. rubra were previously isolated from a spontaneously contaminated system. None of the contaminants caused formation of phenolic or other off-flavour compounds in detectable levels.

SELECTIVE DETERMINATION OF β‐GLUCAN OF DIFFERING MOLECULAR SIZE, USING THE CALCOFLUOR‐FLUORIMETRIC FLOW‐INJECTION‐ANALYSIS (FIA) METHOD

Abstract: When using the calcofluor-fluorimetric flow-injection-analysis (FIA) method to determine β-glucan in wort and beer, the actual range of β-glucan molecular weights effectively complexed by the calcofluor, and consequently the total amount detected, is dependent on the ionic strength of the eluent. In the base eluent of very low ionic strength (20 ppm of calcofluor in aqueous 0.1 M TRIS, pH = 11), only β-glucan molecules of molecular weight greater than approximately 200, 000 daltons are fully complexed by calcofluor, and consequently fully detected. As the molecular weight of β-glucan molecules decreases, β-glucan is only partially complexed by calcofluor, and hence partially detected. By increasing the ionic strength of the base eluent through adding successive amounts of NaCl up to a maximum of 1%, the molecular weight of β-glucan which can be detected by the method decreases down to about 65, 000 daltons, whereas the molecular weights below about 10,000 daltons are not significantly complexed nor detected. Different size ranges of β-glucan have been isolated and characterized by enzymatic degradation of high molecular weight standard β-glucan, followed by classical gel permeation chromatography (GPC), using Sephacryl S-400 HR as stationary phase, pure water as eluent, and dextrans as molecular weight markers.

Effect of ammonia on the malting losses of some improved nigerian sorghum varieties

Abstract: The effect of ammonia treatment as steep liquor on the malting losses and other malting properties of 2 Nigerian sorghum varieties was investigated. Steeping the kernel in 0.1 N ammonia solution for various steeping periods (0 to 18 h) reduced malting losses by suppressing the growth of acrospires. However, mouldiness was not prevented, enzyme development, cold and hot water extracts of the malt were significantly reduced by the application of this chemical. Kernels steeped in 0.3N ammonia solution did not germinate. Malting with ammonia solution may be useful for minimizing malting loss at the expense of optimum development of hydrolytic enzymes, provided the malt produced will only provide malty flavour in beer and external enzymes will be added during processing.

Studies on yeast differentiation using organic acid metabolites part 1. development of methodology using high performance liquid chromatography

Abstract: The separation of organic acids on the column Aminex HPX-87H from Bio-Rad is described. The relationship between column temperature and retention time was studied for both sulphuric and phosphoric acid eluants and an analytical scheme using 0.2% (v/v) phosphoric acid was developed. While the procedure is designed for the commonly occurring non-volatile acid metabolites it was demonstrated that conditions could be established for the analysis of fatty acids to C10. Difficulties in the qualitative and quantitative analysis of organic acids in beer are discussed.

Measurement of endogenous oxygen uptake rates of brewers' yeasts

Abstract: The oxygen requirement of brewers' yeast varies with both the yeast strain and the physiological condition of the yeast and it has been suggested that an estimate of the amount required can be obtained from yeast oxygen uptake values (qO2). Using two techniques (a batch aeration method and a continuous aeration method) it has been shown that the qO2 value can change with time during the evaluation, due to physiological changes in the yeast. Since an assessment of the oxygen requirement is dependent on a representative measurement of qO2 value, tests designed to estimate this parameter should incorporate the following features: (i) Access of the yeast to oxygen should be restricted during sampling and at all times prior to analysis, (ii) qO2 measurements should be made immediately before the yeast is pitched in the brewery, (iii) qO2 value should be expressed on a per cell basis in order to eliminate the need for (time consuming) dry weight determinations. Time dependent changes in qO2 values, which take place during the assay, can affect the precision of the test results. It has been found that the use of high concentrations of cells (1–2 g dry weight Litre−1) reduces this error.

Analytical control of cider production by two technological methods

Abstract: Two cider-production procedures involving direct fermentation of apple juice and a prefermentative clarification step or defecation were controlled microbiologically, while chemical monitoring of the major sugars, polyalcohols and organic acids produced during the fermentation was carried out by HPLC. The defecation process markedly slows down alcoholic fermentation and the malolactic conversion. Good correlations between the contents of D(–) lactate and volatile acidity were obtained for the ciders studied, which indicates that the increased volatile acidity of the ciders was basically a result of metabolism mediated by lactic-acid bacteria, the yield being higher in barrels where enzymatic defecation was not applied. Sucrose was rapidly hydrolysed in the first step of the fermentation process, while glucose is the preferential carbon source for the yeasts. Citric acid was produced by the yeasts in the first step of the fermentation process and was later taken up by these micro-organisms. Conversion of quinic and shikimic acids seemed to point to a signicant activity of heterofermentative lactic-acid bacteria in storage and maturation of ciders.

Cold water extract of malts: soluble carbohydrate and malting behaviour

Abstract: A rapid and simple method for the determination of the carbohydrate fraction of the Cold Water Extract of malts is described. The extraction is preceded by treatment of the malt with barium hydroxide, which is then removed by precipitation with zinc sulphate. This both deactivates enzymes and prevents solubilization of protein. The method was modified so that it was both faster and used smaller samples. A sustainable rate of 80 samples per day can be tested by one operator. This method was used to follow the pattern of modification through malted grain by analysis of pearler residues. Malting and non-malting cultivars differed in the localization of modification through the grain, with modification confined to the outer layers in non-malting cultivars. The method was also used to measure the proportion of soluble carbohydrate formed during malting with increasing modification. The proportion of extract solubilized during malting by malting cultivars was less than that solubilized by feed cultivars.

Tests for selection of malting quality using unmodified barley

Abstract: Various tests for malting potential based on unmodified barley were evaluated. These were based on NearInfraRed Reflectance Spectrophotometry (NIR), sedimentation of meals in cold alcohol or Lactic Acid/Sodium dodecyl sulphate solution, the content of total β glucan as measured by the viscosity of acidic extracts. NIR and sedimentation in Lactic Acid/SDS were found to be the most applicable to the breeding programme at this Institute, whereas the methods based on total β glucan or sedimentation in cold alcohol were unsuitable. The method based on soluble β glucan was only suitable to a breeding programme in which parents with known high β glucan content were used. An hypothesis for the contribution of total β glucan to malting quality is presented. None of the tests investigated were affected by declining dormancy or water sensitivity in the grain.

Kar1‐mediated transformation of brewing yeast

Abstract: Transfer of plasmid between nuclei has been observed in heterokaryons obtained from kar1 × KAR1 crosses3. On this basis, brewing yeast strain CC45 was forced to mate with K5-5A, a kar1 laboratory strain bearing plasmid YEpCR21. This multicopy plasmid carries the gene cyh2 and determines a dominant resistance to cycloheximide. Heteroplasmons having a CC45 nucleus and hosting YEpCR21 were obtained. Plasmid stability and brewing performance have been studied. The utility of kar1-mediated plasmid transference as an alternative method to transform brewing yeast is discussed. Advantages of YEpCR21 as a vector cloning for brewing yeast are considered as well.

The determination of dimethyl sulphide in beer by headspace gas chromatography — a collaborative investigation of precision

Abstract: A method for the determination of dimethyl sulphide in beer by headspace gas chromatography has been collaboratively tested within ten laboratories of one brewing group at 3 levels from 19.8 to 52.4 μg/litre. The repeatability values (r35 were found to be independent of concentration, but a strong linear relationship was found between the mean values (m) and the reproducibility value (R35). The precision data can be summarised as r35 = 3.3 μg/litre, R35 = 3.66 + 0.168 μg/litre.

The influence of grain components on infusion mash performance

Abstract: The conversion of malt starch depends on the availability of water in the mash. At liquor to grist ratios of 3:1 or more, conversion is independent of the quantity of water present. At liquor to grist ratios of 2:1 or lower the amount of starch converted is proportional to the amount of water present. The presence of other water-binding molecules, such as maltose, beta-glucan, or pentosan increases the water dependence of the mash. The presence of protein per se does not affect water availability. However, since the starch content of grain is inversely proportional to the nitrogen level, low nitrogen malts require more water for complete conversion than those with higher nitrogen. The effective gelatinization of an isothermal adjunct mash may also depend on the amount of water available.

Scotch malt whisky distillers' malted barley specifications the concept of fermentable extract — ten years on

Abstract: The validity of the Recommended Methods used as a basis for trading malt by some maltsters and distillers for the decade 1979–1988, during which time there have been some major malting and distilling process changes, have been reviewed. In the ten years, the barley varieties used gradually changed, the use of indirect fired malt kilning, often employing gentler kilning regimes, became widely used, and there was a general move to lauter-type mash tuns. The overall effect of these changes has been a rise in distillery yields. The validity of the fermentability method has been checked and it was confirmed that the attenuation factor of 0.814 remains valid. The calculations of % Fermentable Extract and the Predicted Spirit Yield remain meaningful, and no other such system has been published to challenge the current Recommended Methods.

The use of partially-modified barley for malting quality assessment

Abstract: A series of tests based on the changes in the characteristics of barley caused by partial malting were investigated for selection of progeny with high malting potential from a breeding programme. The characteristics of these partially-modified barleys were investigated using NearInfraRed Reflectance Spectrophotometry (NIR), Pearling Resistance (PR), changes in Viscosity of Acidic Extracts, and changes in weight and translucency of the cut surface of boiled grains. NIR carried out on “day-malts” was found to be accurate, whereas other methods were insufficiently accurate for selection.

The cambridge prize lecture 1989: applications of column chromatography to the analysis of brewing raw materials, wort and beer

Abstract: The applications of column chromatographic methods of analysis to the investigation of the nitrogenous and) carbohydrate constituents of brewing raw materials, wort and beer are reviewed.