A MICROBIOLOGICAL EVALUATION OF BARLEY MALT PRODUCTION

The development of the microflora of barley malt was examined by direct and dilution plating. At all stages of the malting process mesophilic bacteria predominated. Viable counts of bacteria on green malt were 85–600 times greater than on the original barley, but fell to less than one-half of the original level with kilning. Corresponding increases in yeast and, especially, mould counts during malting were smaller. The yeast-like mould Geotrichum candidum was prominent in green malt. Although counts of yeasts and most moulds were considerably reduced by kilning, Mucor spp. proliferated during kilning.     

EVALUATION OF BARLEY AND MALT QUALITY USING NEAR-INFRARED REFLECTANCE TECHNIQUES

A scanning near-infrared reflectance spectrophotometer was calibrated for the prediction of barley aleurone colour and malt moisture. The malt moisture was predicted on malt ground for the determination of malt extract (coarse grind) making the method suitable for moisture correction in malt extract estimation. Calibrations for the prediction of malt extract and endosperm modification from barley and malt were also attempted. A correlation (r= 0.851 n = 135) was found between malt hot water extract and the percentage of the endosperm estimated as being modified by microscopy following staining with Calcofluor. Probably because of this influence of modification on malt extract, the use of near-infrared reflectance to predict malt extract was most successful at predicting the malt extract values obtained following micro-malting in the absence of the additives, gibberellic acid and potassium bromate.     

AREAS OF ABSORPTION RELATING TO MALT EXTRACT VALUE IN MODIFIED NEAR INFRA-RED SPECTRA OF BARLEY FLOUR

Determinations of milling energy, nitrogen, acid-soluble beta glucan and malt extract after micromalting, were made on grain samples of twenty nine barley cultivars. In addition the flour from unmalted grains was scanned over the near infra-red spectrum, and the scan data were subjected to a principal components analysis (PC). Predicted malt extract values resulting from an NIR multiple regression equation with PC terms, correlated well (r = 0.934) with the manual extract values. This confirms previous evidence that malt extract value depends largely on constituents in the resting grain, rather than on malt enzymes. An attempt to locate NIR absorptions relating to malting quality was made by restructuring the NIR spectrum of the samples according to the weightings modified by the regression coefficients in the PC regression equation for hot water extract value. The spectrum reconstructed in this way showed a number of absorption peaks and troughs. From comparison with previous NIR scans it was concluded that a strong peak at the wavelength 2100 nm was due to a starch absorption and this together with minor starch overtone peaks correlated positively with malt extract. Troughs at 2180 nm, 1980 nm and 1700 nm indicated a negative association between malt extract and some proteins. There were also wide troughs at 1830 and 2330 nm indicating a negative relationship between malt extract and beta glucan. Other peaks and troughs in the reconstructed spectrum could not readily be assigned to a constituent. A reconstructed protein spectrum consisted of peaks and troughs that agreed with previous assignations for protein absorbancies. A milling energy reconstruction was approximately the inverse of the malt extract spectrum, and an acid-soluble beta glucan reconstruction was relatively featureless and appeared to be due to the effects of particle size variations.     

EVALUATION OF MILLS FOR MALT ANALYSIS

Two versions of Seck mill and one rotating Disc mill have been evaluated to assess their suitability for malt analysis and particularly for measurement of the Hot Water Extract as described in the Recommended Methods of Analysis of the Institute of Brewing. Measurements of Hot Water Extract and sieve analyses were carried out on a range of malts of different modifications and moisture contents to determine the reproducibility and grinding characteristics of each mill. The mills proved equally reliable for the measurement of Hot Water Extract despite differences in roll speed and despite differences in the sieve analyses. Furthermore, the mills in new condition gave values somewhat higher than those obtained with the mills currently used in commercial laboratories. The rotating Disc mill gave reproducible values for differences in extract using the Institute mashing procedure on coarse and fine grists. It also proved easier to operate than the Seck mills.     

EFFECTS OF GAMMA IRRADIATION OF BARLEY AND MALT ON MALTING QUALITY

Two two-rowed barley cultivars, Tokak and Clerine, were irradiated at two different dose ranges (0.05–0.75 kGy and 0.5–5.0 kGy) using a ⁶⁰Co source. Irradiation of barley at the medium levels before malting had detrimental effects on most of the malt quality criteria. The detrimental effects of irradiation was lower at doses up to 0.25 kGy. Irradiation of malt samples caused either slight or no deterioration of quality characteristics .     

RELATIONSHIP BETWEEN FUSARIUM INFESTATION OF BARLEY AND THE GUSHING POTENTIAL OF MALT

Fifty barley samples, displaying a range of 0 to 100% kernels infested with Fusarium, were collected in North Dakota, South Dakota, and Minnesota during the harvest of 1994. Samples were micromalted, and the levels of the fungal metabolites, deoxynivalenol and ergosterol, were determined. Fusarium infestation and the levels of fungal metabolites were evaluated as predictors of gushing in laboratory trials. Malt samples which were infested with Fusarium or contaminated with the fungal metabolites exhibited a propensity to gush. However, only the levels of deoxynivalenol and ergosterol were found to be strongly correlated with the actual amount of gushing observed. This suggests that their production may parallel that of the component which actual causes gushing, and that screening barley and malt for these metabolites, may offer a means of reducing gushing problems in the brewery. Determination of deoxynivalenol is rapid, when it is present, and necessary because of food safety and malt quality concerns.     

THE USE OF HORDEIN FRACTIONS TO ESTIMATE PROTEOLYTIC ACTIVITY IN BARLEY AND MALT

When the natural barley protein, hordein, is used as a substrate for the assay of exopeptidase and endopeptidase activity in green malts, the enzymic activities found differ significantly from those obtained using non-barley substrates such as dipeptides, gelatin or haemoglobin. Malts having similar total levels of carboxypeptidases as measured using non-barley substrates showed considerable variation in the extent to which these enzymes break down barley hordein. Malts also varied more in their endopeptidase activity with hordein than in their ability to digest gelatin or haemoglobin. Analyses of hordein by gel chromatography and gel electrophoresis indicate that it consists of eight main components, which can be divided into three groups of proteins, with molecular weights in the regions of 15,000, 65,000 and ≥ 100,000. Barley samples differed in their relative contents of these proteins and this variation could be rapidly assessed using gel electrophoresis.     

VARIETAL IDENTIFICATION OF BARLEY AND MALT*

A vertical polyacrylamide — SDS electrophoretic technique, including whole protein extraction and staining steps, was improved with a view to developing it for routine laboratory use with single barley kernels. The pattern consisted of 4 zones: A (albumins-globulins). B and C (hordeins) and D (possibly glutelins) displaying unequal varietal polymorphisms (1, 13, 13 and 4 types respectively). 28% of the barley samples (77 varieties), including most cultivars grown in France, could be unambiguously identified from qualitative differences only, in the B, C and D zones. Adding three other characteristics (hairs and furrow hairiness, peroxidase, zymogram, esterase zymogram), as many as 78% of the varieties could be identified, the other 22% consisting of very closely related barleys. After slight modification of protein extraction conditions, the same methods could be used with malt, based on the same electrophoretic types. A graphic tablet connected to a microcomputer was used for automatic acquisitions of records and comparisons of electrophoretic data.     

A RAPID SMALL SCALE METHOD FOR THE DETERMINATION OF MALT EXTRACT

A rapid, small-scale method was developed using 1 g of ground malt mashed in 10 ml of water at 65°C. The extract was centrifuged and the specific gravity determined using a density meter. The method was compared with an earlier small-scale method and the Institute of Brewing method and was found to have good precision (CV 1.2%). Absolute malt extract values were not significantly different (P = 0.05) from those obtained by the IOB method.     

INSTITUTE OF BREWING: ANALYSIS COMMITTEE RECOMMENDED MILL FOR MALT ANALYSIS

The Miag Disc Mill is now the standard mill for malt analysis. A method of setting the gap between the grinding discs by mean of a feeler gauge has been adopted. Using the recommended setting 5.0 for the measurement of Hot Water Extract the replication error is 0.8 litre °/kg. The error due to the mills is negligible compared with the errors arising from the remaining parts of the measurement.     

DEGRADATION OF HORDEIN BY THE PROTEOLYTIC ENZYMES OF BARLEY AND MALT

Development of the endo- and exo-peptidases that degrade the major barley storage protein, hordein, during malting is affected by treatment with gibberellic acid and potassium bromate, and also by the moisture levels attained during malting. For a given set of malting conditions, cultivars had different peptidase activities, but there were no consistent comparable differences between cultivars in amylase or endo-β-1,3 glucanase activities.     

A RAPID AND SIMPLE METHOD FOR THE DETERMINATION OF STARCH AND β-GLUCAN IN BARLEY AND MALT

A simple and precise method suitable for the routine determination of starch and β-glucan in barley and malt is described. Perchloric acid (50 mM) was used to effect rapid (3 min) and exhaustive extraction of both glucans which were then measured directly from this single extract by specific enzymic hydrolysis of the individual glucans to glucose. The glucose was also measured enzymically. Little or no acid hydrolysis of starch or β-glucan was observed under the extraction conditions used; most or all of the free glucose could be attributed to hydrolysis of sucrose. Complete solubilisation of the gum and hemicellulosic components of β-glucan was achieved. Preincubation of the acid extracts with protease prior to amyloglucosidase digestion resulted in higher measurements (approximately 4% w/w) of starch. The method was used to measure the levels of starch and β-glucan in five varieties of barley with contrasting malting quality, in micro-malts prepared from these samples and in commercial lager and ale malts.     

BARLEY AND MALT ANALYSIS—A REVIEW

This review describes the developments in barley and malt analysis since 1960, the suitability of analyses commonly used at present, and changes which are likely to occur in future. The review is not restricted to analyses suitable for brewers and distillers but also discusses methods used in the control of malting and in the selection of barley for malting.     

QUANTITATIVE IMMUNOELECTROPHORESIS OF BARLEY AND MALT PROTEINS

Quantitative immunoelectrophoresis techniques were applied to the study of barley and malt proteins. By crossed immunoelectrophoresis of malt more than 54 immunochemically distinct proteins were distinguished, whereas only 24 proteins have been included in the E.B.C. system of reference based on electro-immunodiffusion. * 1 Electrophoretic separation followed by immunodiffusion (immunoelectrophoresis ad modum Grabar¹¹) is termed “electro-immunodiffusion” in this paper. The use of this term is substantiated in the initial section of “Results and Discussion”.
Crossed immunoelectrophoresis was also used to estimate four aminopeptidases in organs of germinating barley, and to demonstrate non-identity, identity and partial identity between barley and malt proteins. Tandem crossed immunoelectrophoresis was used to compare the proteins in extracts of barley and malt and rocket immunoelectrophoresis to determine an α-amylase in germinating barley. Fused rocket immunoelectrophoresis was used to detect elution patterns of individual barley proteins after ion exchange chromatography, and line immunoelectrophoresis to compare three barley antisera. Advantages of quantitative immunoelectrophoresis over electro-immunodiffusion are demonstrated and discussed. A new system of reference for barley and malt proteins based on crossed immunoelectrophoresis is suggested.     

THE CAMBRIDGE PRIZE LECTURE 1995: INDIRECT AND DIRECT CONTRIBUTIONS OF BARLEY MALT TO BREWING

The suitability of barley malt as a raw material for brewing is determined by an amalgamation of “indirect” and “direct” contributions to the beer produced. Indirect contributions are considered as those which affect the quality of the brewing process performance whereas direct contributions are considered as those which affect the quality of the product. As a potential indirect contribution of malt to brewing quality evidence is presented that barley malt contains a flocculent which influences mash filterability. As a potential direct contribution of barley malt to beer quality evidence is presented that the mineral silicate found in beer may have a role in moderating dietary aluminium.     

THE EFFECT OF KILNING ON THE CAPABILITY OF MALT TO OXIDISE LIPIDS

The influence of kilning on the ability of malt to oxidise lipids was studied. Barley was malted with a standard programme and subsequently dried with varying kilning procedures. The capability of samples taken during kilning to oxidise lipids was determined by the lipoxygenase (LOX) reaction, i.e. by measuring O₂ consumption in an aqueous suspension of samples upon addition of excess amounts of exogenous linoleic acid. Various kilning programmes from isothermal low-temperature kilnings to kilnings with varying temperature profiles induced a two- to threefold increase in the rate of the LOX reaction in the samples taken during the first two to six hours of kilning. However, when lipid changes in the intact kernels were measured, oxidation of the endogenous malt lipids was very limited during the first half of kilning. Furthermore, the rate of the LOX reaction decreased in samples taken during the latter part of kilning, the rate of decrease depending on the kilning programme and especially the final curing temperatures. These results indicate that a possible risk of a marked ability to oxidise lipids remains at moderate kilning temperatures. In conclusion, kilning induces a significant capability to oxidise lipids but does not affect the fatty acid composition of whole kernels. However, in aqueous suspensions of ground malt the oxidative instability created might lead to oxidation of lipids .     

AN APPROACH TO THE ESTIMATION OF BREWING QUALITY IN BARLEY AND MALT

Methods of assessing the brewing qualities of new varieties are reviewed. A new method for making this assessment is proposed. This is ideally a three-step process but it would be possible to eliminate the third, costly, step without severe loss of effectiveness. The use of the new method is illustrated by reference to trials using 251 samples from recent trials in France.     

RECOGNITION OF TWO LIPASES FROM BARLEY AND GREEN MALT

Lipase was extracted from ground samples of germinating and ungerminated barley, using the detergent Triton X-100. Enzyme activity, measured by the release of oleic acid from radioactively labelled triolein, was approximately half that in suspensions of barley flour. Two distinct lipases, both active at neutral pHs, and having similar molecular weights (around 400,000) but differing in their ionic properties, were isolated from barley. The more abundant lipase was found mainly in the embryo, while the other was located in the endosperm. Both total and extractable lipase activity increased during germination.     

THE INSTITUTE OF BREWING ANALYSIS COMMITTEE CURRENT OUTLOOK ON MALT ANALYSIS

After discussions with the Barley Advisory Committee and the Technical Committee of the Maltsters' Association, it was decided that the Analysis Committee will seek to include in Recommended Methods, additional analytical procedures, which will be helpful in predicting malt preformance in particular brewing circumstances. However, it was first necessary to find a reliable and reproducible mill suitable for measurement of Hot Water Extract, together with such additional methods. A rotating disc mill (Miag) has been evaluated and provides substantial advantages over Seck mills, so that it will be introduced as the standard mill from 1st January 1977 and will be the only permitted mill from 1st January 1978. Introduction of a new mill will cause a shift in the level of extract measured. However, in the longer term it is intended that measurement of the difference in extract from fine and coarse grists, both of which can be produced readily with the rotating disc mill, will supplant the present measurement of Hot Water Extract in Recommended Methods.     

EFFECTS OF THE MYCOTOXINS DIACETOXYSCIRPENOL AND DEOXYNIVALENOL ON MALTING CHARACTERISTICS OF BARLEY

In germination tests, the trichothene diacetoxyscerpanol (DAS) caused reductions in the number and total length of rootlets, and the length of the coleoptile, developing from excised barley embryos, but the effects were less than those of T-2 toxin. Rootlet and coleoptile growth was also inhibited during micromating of barley artificially contaminated with DAS before steeping, whilst α-amylase activity of finished malts were reduced by up to 49%, and α-amino nitrogen levels in worts were also lower than in controls. The effects of deoxynivalenol (DON) were less than those of DAS, e.g. the reduction in α-amylase activity caused by DON applied at the rate of 50 μg g-1 grain was less than one-half of that caused by 20 μg DAS g^?1.