THE EFFECTS OF NITROSODIMETHYLAMINE PALLIATIVES ON MALT PROPERTIES*

The mechanisms of formation of NDMA in malting are briefly discussed to allow grouping of methods for NOMA control. The techniques to control NDMA are considered in relation to their effect on other malt properties and the difficulties of balancing all aspects to achieve a malt specification is highlighted. The use of low NO_x conditions, the lowering of hordenine production, the prevention of hordenine nitrosation, the reduction of nitroso-hordenine breakdown and the removal of DMA and NDMA in kiln exhaust are all considered with the aim of producing malt of brewing quality with NDMA less than 5ppb. The outlook for the future is briefly examined when it seems likely that indirect firing of malt may have to be employed.     

DIASTATIC POWER IN MALTED BARLEY: CONTRIBUTIONS OF MALT PARAMETERS TO ITS DEVELOPMENT AND THE POTENTIAL OF BARLEY GRAIN BETA-AMYLASE TO PREDICT MALT DIASTATIC POWER*

The malt parameters alpha-amylase, beta-amylase, limit dextrinase, protein and beta-glucan were each linearly related to the diastatic power measured in malted barley, with beta-amylase having the highest coefficient of variation (r² = 0.63). Multivariate regression analysis derived a model comprising beta-amylase, alpna-amylase and limit dextrinase, with no significant interactions (p < 0.05). The model accounted for over 79% of the variation in diastatic power. These three malt parameters might be usefully targeted in breeding programs aiming to improve diastatic power in malted barley. The analysis of samples from two harvests showed that malt diastatic power is also significantly related to total grain beta-amylase activity (r² ranging up to 0.61). This suggests that total grain beta-amylase can be used as a screening procedure for the diastatic power of experimental barley breeding lines. However the relationship is subject to significant genotypic (cultivar) and environmental influences (p < 0.001) and regression analysis found that diastatic power was significantly related to beta-amylase and cultivar (r² = 0.76). Thus the use of a single regression curve comprising pooled data from several cultivars to relate diastatic power and total grain beta-amylase might be misleading. For barley breeding programs, the most effective use of the beta-amylase model as a criterion to identify experimental lines with unacceptable diastatic powers is to apply as a benchmark the total grain beta-amylase activity of a reference variety at each location, accepting lines with consistently higher beta-amylase activities for micromalting and further testing.     

DEVELOPMENT OF METHODS FOR THE CHARACTERISATION OF NON-VOLATILE N-NITROSO COMPOUNDS IN MALT

The effect of pH on extractability and the chromatographic separation of non-volatile N-nitroso compounds in aqueous wort extracts of malt have been studied. The apparent total N-nitroso compounds (ATNC) contain acidic functional groups and consist of a large number of minor components.     

THE EFFECTS OF INCREASED STEEPING TEMPERATURES ON ENZYME DEVELOPMENT IN MALT

Malts produced by steeping at 30 °C for a total of 24 h including two air rests, frequently give the same results in routine analyses as do malts produced by steeping at 16°C for longer periods. However, the corresponding worts often filter more slowly under controlled laboratory conditions. The increased steeping temperatures can delay or reduce development of endopeptidase and β-glucan solubitase, but generally have little effect on the activity of α-amylase, carboxypeptidase, or endo-β-glucanase. The problems with wort separation are most probably due to high molecular weight β-glucan and disulphide-linked hordein persisting at the end of malting.     

THE β-AMYLASE ENZYMES OF BARLEY AND MALT: I. PURIFICATION OF THE MALT ENZYMES*

Two β-amylase enzymes from malted barley were purified by successively fractionating an extract on CM-cellulose, Sephadex G-75, and DEAE-cellulose. The procedure resulted in a net recovery of 10% of the initial activity and a 10-fold and 16-fold purification of the individual enzymes. Each enzyme migrated as a single protein band during disc electrophoresis at pH 4·5, but each purified protein extract produced two active protein bands at pH 8·9. This heterogeneity within components appeared to be due to oxidation of essential SH groups at high pH that caused loss of enzymic activity.     

ROLE OF ALPHA-GLUCOSIDASE IN THE FERMENTABLE SUGAR COMPOSITION OF SORGHUM MALT MASHES*

The cause of the high glucose to maltose ratio in sorghum malt worts was studied. Mashing temperature and pH strongly affected both the amount of glucose and the proportion of glucose relative to total fermentable sugars. The relative proportion of glucose was higher when mashing was performed. at pH 4.0, close to the pH optimum for sorghum alpha-glucosidase, than at the natural pH of the mash (pH 6.0–5.5). Mashing according to the EBC procedure using an enzymic malt extract with pre-cooked malt insoluble solids producing a wort containing maltose and glucose in an approximately 4:1 ratio, whereas mashing with a malt extract without pre-cooking the malt insoluble solids resulted in a wort with approximately equal amounts of maltose and glucose. Both treatments gave the same quantity of total fermentable sugars and amount of wort extract. Sorghum alpha-glucosidase was confirmed to be highly insoluble in water. All or virtually all activity was associated with the insoluble solids. Hence, it appears that the high amount of glucose formed when sorghum malt is mashed conventionally is due to alpha-glucosidase activity. Pre-cooking the malt insoluble solids inactivates the alpha-glucosidase, preventing the hydrolysis of maltose to glucose.     

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.     

INACTIVATION OF MALT PEPTIDASES DURING MASHING*

Malt contains at least eight different peptidases: three carboxypeptidases (pH optima 4·8, 5·2, 5·7), three aminopeptidases active on aminoacyl-β-naphthylamides (pH optima in hydrolysis of peptides at pH 5·8-6 5), and two (amino)peptidases acting on Leu-Tyr and Ala-Gly at higher pH (pH optima 8·6, 7·8). We have studied the progressive inactivation of these peptidases during mashing with a temperature programme from 45° to 70° C (pH 5·8 → 5·7). All peptidases were stable at 45° C. The five aminopeptidases were inactivated at different rates during a 30-min incubation at 55° C. The carboxypeptidases retained 70–100% of their activities at this temperature, and one of them had 40% residual activity after 60 min at 70° C. Liberation of amino acids continued at a considerable rate during the incubation at 70° C, probably catalysed by the heat-stable carboxypeptidase. Malt carboxypeptidases are therefore more heat-stable in mashing conditions than the aminopeptidases. This property, in combination with their high activities and suitable pH optima, makes them the most important enzymes in the production of free amino acids in mashing.     

THE QUALITATIVE AND QUANTITATIVE MEASUREMENT OF PEAT SMOKE ON DISTILLER'S MALT*

In the course of developing a novel peating process it became apparent that the present methods for determining the intensity of peat smoke on distiller's malt are inadequate. While the colorimetric test for peat phenols is fairly accurate at low levels, it can give misleading results with highly peated malts. Furthermore, the 4-aminophenazone reagent used in this test is not sensitive to some of the major phenol constituents of peat smoke. New qualitative gas chromatographic techniques, which monitor a wider spectrum of peat smoke constituents, are now presented together with some suggested improvements to the existing quantitative colorometric analysis.     

DEVELOPMENT OF AMYLOLYTIC ACTIVITIES IN SORGHUM AND BARLEY MALT

A Nigeria-grown sorghum cultivar was observed to develop more Diastatic Power (DP) and β-amylolytic activity than a previously studied sorghum cultivar grown in Australia. Barley malt produced more Diastatic Power and β-amylolytic activity than the Nigeria-grown sorghum cultivar. In general, the kilned barley malt retained less α-amylolytic activity than kilned sorghum malt. The different diastatic potential of sorghum cultivars may reflect differences in genetic character or growth conditions.     

PREDICTION OF THE LAUTERING PERFORMANCE OF MALT

The lautering performance of malt in a laboratory column can be predicted from the results of a series of simple analytical estimations. For normal commercial malts, prediction of lautering rates requires measurement of particle size after passage through a roller mill, combined with results from a simple sedimentation test. For poorly-modified malts a laboratory scale mashing operation is additionally required. This allows estimation of the volume of fine particles in the exhausted mash bed and a measurement of wort viscosity.     

DEVELOPMENT AND USE OF A METHOD FOR DETERMINATION OF MALT FERMENTABILITY

A method for the determination of the fermentability of unboiled, filtered, malt Hot Water Extracts has been developed. The wort is fermented under carefully controlled conditions, using fresh distillers' yeast. Knowledge of a malt's extract and fermentability allows calculation of its fermentable extract content, which allows spirit yield prediction, and the method is in use as a basis for Malt Purchase Specifications.     

STUDIES ON THE MYCOFLORA OF MALT

The mycoflora of malt which caused gushing beer has been investigated and compared with the mycoflora of malt from nine malting plants in Sweden, Denmark, Finland and England. Malt which caused gushing beer was found to contain a high proportion of grains contaminated by Aspergillus, Penicillium and Rhizopus. The commonest species isolated were found to be Aspergillus fumigatus and Aspergillus amstelodami. These fungi occurred on all malt samples investigated independent of their origin. The mycoflora on malt differs greatly from that found on barley. Evidence is presented showing that barley becomes contaminated during the malting process.     

FACTORS GOVERNING THE MILLING OF MALT

A method has been developed using a laboratory 2 roll mill for reproducibly milling malt produced from European Barley (two-row). The procedure can be readily adapted to give grists of similar particle size distribution to those produced by either commercial four or six roll mills. Factors which were considered likely to affect the milling of malt were studied with particular attention to moisture level, the degree of modification, extent of kilning, influence of storage, differences in grain size and extent of steam conditioning. Most of these factors did exert an effect on milling. However, in the majority of cases the values needed to be outside normal commercial limits before substantial changes in milling performance were observed. Studies employing a laboratory mashing system have shown that by using malts containing c.a. 6% moisture it is possible to reduce wort separation times without affecting extract recovery. Steam conditioning can have a marked beneficial effect on the milling performance of malt providing the extent of moisture pick-up is carefully controlled.     

SEPARATION OF NITROGENOUS CONSTITUENTS OF MALT,WORT AND BEER USING HIGH PERFORMANCE LIQUID CHROMATOGRAPHY

High performance liquid chromatography has been used to separate groups of soluble nitrogenous compounds in malt. Malts are extracted with water at 5°C and the nitrogenous components separated using a column packed with a material designed specifically for the analysis of proteins and peptides. The procedure is suitable for routine use and can be readily adapted to study changes in the development of nitrogenous compounds during the brewing process.     

THE DETERMINATION OF SULPHUR DIOXIDE IN MALT

The Institute of Brewing Recommended Method for the determination of sulphur dioxide in beer has been modified for determination in malt. Three inter-laboratory trials are reported and the resulting procedure is described. It has the advantages of being well tried in its general form and employing relatively cheap equipment. While the inter-laboratory reproducibility achieved was not particularly good the method is published for use in laboratories where it may fulfil a present need.     

RECOMMENDED METHODS OF ANALYSIS OF BARLEY,MALT AND ADJUNCTS ALTERNATIVE TITRATION PROCEDURE FOR THE DETERMINATION OF THE DIASTATIC ACTIVITY OF MALT

The Sub-Committee was unable to recommend the determination of wort fermentability as an alternative to the determination of diastatic activity in the evaluation of malts. Potassium ferricyanide solution is recommended as an alternative to Fehling's solution in the determination of the diastatic power of malt because the titration is simpler and the reproducibility of the determination is less dependent on the volume of cold water extract taken for diastasis.     

USE OF THE FRIABILIMETER TO ASSESS HOMOGENEITY OF MALT

A method has been developed for assessing the homogeneity of a sample of malt using the Friabilimeter. Material retained by the Friabilimeter sieve is further fractionated using a sieve with slits 2·2mm wide by 23mm long, as recommended by the EBC for assessing corn size. Material composed of unmodified grains and large pieces of endosperm is collected from the sieve and weighed. This gives a rapid and reproducible estimate of the proportion of unmodified material in the sample. The technique readily detects small quantities of unmodified grain added to a sample of malt. Staining half corns with Calcofluor gives similar scores for homogeneity but with poorer reproducibility and the technique is much slower. Staining with methylene blue gives much lower figures for homogeneity and is also slower and less reproducible than the Friabilimeter method.     

EVALUATION OF THE INFRAALYZER 400 FOR THE ANALYSIS OF BARLEY AND MALT

A collaborative study is described of the use of infra-red reflectance for the evaluation of the analytical characteristics of barley and malt. Transfer of centrally-prepared calibrations to other reflectance machines was found to be possible for moisture content and protein content in barley and malt but not for malt extract or malt modification. The examination of infra-red reflectance results, obtained at different wavelengths, by step-wise ascending regression rather than step-wise descending regression showed that the former was more satisfactory, especially in being more rapid in execution.