THE USE OF PARTIALLY-MODIFIED BARLEY FOR MALTING QUALITY ASSESSMENT

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.     

ENVIRONMENTAL AND VARIETAL DIFFERENCES IN TOTAL β GLUCAN CONTENTS OF BARLEY AND THE EFFECTIVENESS OF ITS BREAKDOWN UNDER DIFFERENT MALTING CONDITIONS

The total β glucan contents of a number of barley varieties grown at different sites in England have been determined using a direct enzyme degradation method. Variations in values for a single variety between sites or between harvests indicates that environmental factors are involved in regulating β glucan formation while the involvement of genetic factors is inferred from the finding that the ranking order for different varieties at each site and at each harvest is similar. A single variety of barley has been micromalted under varying conditions of moisture, temperature, gibberellic acid concentration and germination time and a very close correlation between the total β glucan levels and the fine-concentrated difference values has been obtained. This work confirms the relationship obtained earlier with different varieties of malts under a specific malting schedule, indicating that the relationship is one which is widely applicable. The measurement of total β glucan can therefore be used in the estimation of modification and the prediction of brewhouse yield.     

The Application of Near Infrared Spectroscopy to Evaluate Malting Quality

Near infrared (NIR) spectroscopy is a rapid technique which is used within plant breeding programs for the analysis of many grain traits. This study investigated the application of NIR analysis of wort samples to select malting quality cultivars in a barley breeding program. An automatic sampling and data capture system was developed which consisted of a Perten filter NIR instrument with a flow through cell module operating in transflectance mode interfaced with a computer, peristaltic pump and sample changer. Calibrations for hot water extract, free alpha-amino nitrogen and soluble protein were developed using multiple linear regression analysis based on four wavelength terms for each trait. The correlation coefficients for both calibration and prediction data sets were highly significant (P<0.01) and the standard error of prediction was similar to that obtained by standard methods. Cultivars with known malting quality were included in the experiments and their ranking by NIR was consistent with the standard methods. The reported calibrations have been used for over four years to screen early generation breeding lines for malting quality.     

EVALUATION OF A MICRO-MALTING PROCEDURE USED TO AID A PLANT BREEDING PROGRAMME

A micro-malting and a malt analysis procedure, using less than 40 g of seed, is described and critically appraised as a means of assessing the malting potential of samples generated in a barley breeding programme. Four barley varieties representing a range of malting abilities were used to evaluate the method. The magnitude of variances due to analyst, batch and cumulative experimental errors were compared to variation attributable to variety for 22 characters examined during seed preparation, malt production and malt analysis. For most characters almost all of the variance was due to variety; these included hot water extract, soluble nitrogen, cold water extract, grain nitrogen and thousand corn weight, which are the characters principally used for assessing malting ability. The results show that the procedure is suitable for determining the grain characters and malting potential of the large numbers of samples submitted from breeding trials and also draw attention to those requiring particular care in defining analytical techniques and requiring consistency in application.     

Assessment of Enzymatic Endosperm Modification of Malting Barley Using Individual Grain Analyses

Enzymatic modification of the endosperm of malting barley is a main feature of the malting process. Uneven enzymatic modification of the endosperm (heterogeneity) can cause brewhouse problems. Although there is a general correlation between endosperm modification, beta‐glucan breakdown and endo‐beta‐glucanase development, it is based on average results from sample analyses and may conceal heterogeneity. The primary aim of this work was to use individual grain analyses to investigate factors that control endosperm modification and beta‐glucan breakdown. In terms of beta‐glucan breakdown and physical modification, the barley variety Chariot malted faster than Decanter. However, both varieties showed similar distribution of endo‐beta‐glucanase in individual grains during malting. Further work on individual grains showed that the correlation between beta‐glucan breakdown and endo‐beta‐glucanase activity was not significant. Surprisingly beta‐glucan breakdown did not always correlate with the physical modification of the endosperm. Both these findings suggest that sample analyses of beta‐glucan levels and malt beta‐glucanase activities are not reliable indicators of the degrees of which malt samples are modified during malting. Since the distribution of beta‐glucan in individual grains of the unmalted barley varieties was similar, the total beta‐glucan levels of the original barley did not determine the rate at which beta‐glucan was broken‐down during malting. Although protein studies are at a preliminary stage, the rate of protein breakdown was not correlated with the rate at which beta‐glucan was broken down in the malting grain. It is possible that the physico‐chemical properties of endosperm storage proteins may limit the rate of beta‐glucan breakdown during malting.     

Re‐Assessment of the Half‐Grain Modification Method for Assessing Malt Modification

The half‐grain mashing (modification) method proposed by Palmer (J. Inst. Brew., 1975, 81: 408) was reassessed. The intention was to quantify the differences in malt modification in terms of β‐glucan breakdown and clarify the relationship between β‐glucan breakdown and overall modification of the endosperm during malting. This was carried out at 45°C as well as at 65°C, the percentage of weight loss was recorded and the endosperm residue was analysed for β‐glucan content. In general, weight loss was related to modification. Samples, which were modified at higher levels, lost significantly more material during the half‐grain mashing procedure than those which were under‐modified. At a malting process time of 96 h all the varieties had similar weight loss. After mashing the half grains, the β‐glucan contents of the grain residues showed an apparent increase because of loss of non‐β‐glucan materials. However, over the malting period β‐glucan decreased. Chariot malted faster than the other varieties studied. The β‐glucan levels of this variety were reduced by 78% between 48 and 72 h of germination. Significant levels of β‐glucan were degraded and large quantities of starch and protein were released. During the same period of germination, the corresponding samples of Decanter did not show a significant reduction in β‐glucan levels. In contrast, Brazilian variety MN698 lost endosperm material and β‐glucan rapidly by 48 h. These early results suggest that during malting, extract solubilization may or may not accompany β‐glucan breakdown. Therefore, β‐glucan levels in malt cannot be used as an overall index of modification of the endosperm.     

The Influence of Lactic Acid Bacteria on the Quality of Malt

In this study three strains of lactic acid bacteria were applied during the malting process to evaluate the impact on malt and wort quality. The trials were performed in a micromalting plant simulating an industrial malting programme. The samples were compared to chemically acidified as well as non‐acidified malt. Bacterial cultures were chosen with reference to their enzymatic (proteolytic/amylolytic) activity, or their good acidifying properties. The effects of lactic acid bacteria on wort characteristics were investigated and compared to wort produced from 100% unacidified malt. A chemical food grade lactic acid was also used to acidify the barley for comparison purposes. Characteristics such as pH, extract, colour, viscosity, total soluble nitrogen, free amino nitrogen, apparent fermentability, β‐glucan and lautering performance of the resultant worts were determined. Results showed improved levels of β‐glucanase in the malt although reduced malt friability was observed where LAB was employed. An improved lautering performance, lower wort viscosity and elevated TSN levels were also reported where LAB exhibiting protease activity were applied.     

Barleys Grown as Cultivar Mixtures Compared with Blends Made Before and After Malting,for Effects on Malting Performance

Four barley cultivars were grown in replicated trials at three sites in Scotland in 2000, both as pure stands and in all four possible three‐component mixtures. After harvest, some grain from the pure stands was used to synthesise four blends of three component varieties. Grain from the pure stands, the mixtures and the blends was malted and all samples were assessed for total β‐glucan content. At two of the sites, field grown mixtures were shown to have lower malt β‐glucan than blends made prior to malting, although their grain β‐glucan contents had not been significantly different from the means of the component varieties. At the other site, the mixtures had higher levels of soluble nitrogen than the blends or the means of their component cultivars although, significant differences had not occurred in grain nitrogen contents. Three component blends were also made from the malted grain of the pure stands and hot water extracts were measured on all samples including the blends made before and after malting. There were considerable differences between sites and also between mixtures, blends and the mean of the mixture components when assessed separately. At all sites and for all varietal combinations, field grown mixtures were shown to be equal or superior to blends made after harvesting, in addition to frequently exceeding the mean of their components. It was concluded that the advantages, in β‐glucan or protein modification, associated with mixtures resulted from interactions between components in the growing environment and that interactions in the malting and mashing environments had little if any effect.     

BRAZILIAN HULL-LESS AND MALTING BARLEY GENOTYPES: I. CHEMICAL COMPOSITION AND PARTIAL CHARACTERIZATION

Barley represents an important source of total dietary fiber (TDF) and β‐glucans. The chemical composition and partial characterization of two Brazilian barley experimental lines, hull‐less and malting, are reported. The range in diameter of the A‐ and B‐type granules was similar in both barley lines, 15 to 28 µm and 8 to 10 µm, respectively. Higher values for total starch, damage starch, ash, TDF and insoluble dietary fiber (IDF) were observed in the malting line while β‐glucan content was similar in both samples. The malting barley line had higher values of total isolated starch, as well as residual protein and total lipids in starch. The starch from the hull‐less barley line had lower swelling power and higher solubility than malting barley.     

Effects of Grain and Malt â‐Glucan on Distilling Quality in a Population of Hull‐less Barley

A population of barley lines, derived by mutation in the hull‐less variety, Penthouse, was included in a replicated trial, along with Penthouse and the hulled malting cultivar, Optic. Samples were assessed for a range of grain quality traits, then malted, with germination for either 4 or 5 days, prior to kilning. Most lines had grain β‐glucan contents lower than that of Penthouse, but there was no significant correlation between grain and malt β‐glucan content. Malt β‐glucan levels were indicative of differences in cell wall breakdown between 4 and 5 days germination, but negative associations with distilling parameters Extract and Alcohol Yield, were not statistically significant. It was concluded that the lines differed in the rate and extent of cell wall breakdown and that grain shape may influence modification in distal parts of the grain. However, a malting regime, optimised to suit Optic may be less suited to discriminating between hull‐less lines of reasonable quality.     

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.     

Malting Performance of Normal Huskless and Acid‐Dehusked Barley Samples

Sulphuric acid dehusked barley had a higher germinative energy and lower microbial infection than normal huskless (naked) barley, suggesting that the pericarp layer harboured microbial infection which may have limited the germination rate. Dehusking the normal huskless barley using sulphuric acid resulted in lower microbial infection, and increased germinative energy. The normal huskless barley sample had a higher β‐glucan content than the acid‐dehusked barley and had slower β‐glucan breakdown during malting. This resulted in the release of seven times more β‐glucan during mashing, and the production of wort of higher viscosity. The normal huskless barley sample had a higher total nitrogen content than the acid‐dehusked barley but both samples produced similar levels of amylolytic (α‐ and β‐amylase) activity over the same malting period. No direct correlation was found between barley total nitrogen level and the amylolytic activity of the malt. When barley loses its husk at harvest, the embryo is exposed and may be damaged. This may result in uneven germination which can reduce malting performance and hence malt quality.     

AN AUTOMATED MICRO-MALTING UNIT FOR QUALITY ASSESSMENT IN A BARLEY BREEDING PROGRAMME

An automated micro-malting unit for quality evaluation of lines from a barley breeding programme, with the capacity to process 87 samples of 15 g grain or up to 129 samples of 5 g grain each weekly batch, is described. Aspects of the design of the equipment, in particular the malting chamber and sample containers, are discussed. The malting unit provided a relatively uniform environment within a batch when tested by malting replicates of one cultivar. There were very small gradients within the malting chamber during steeping and modification which resulted in small differences in the hot water extract of malts depending on container position. However, replicate samples within a batch gave mean extract values with good overall precision with a coefficient of variation of 0·6%. Furthermore, the equipment gave reproducible malting conditions from batch to batch. Hot water extract values of six barleys did not differ significantly between three successive malting batches and the major contribution to variance for all the malting characters measured in this case was attributed to differences between cultivars.     

The influence of steep regime and germination period on the malting properties of some hull‐less barley lines

Following field trials in 2008 and 2010, six lines, derived by mutation in the hull‐less barley cultivar Penthouse, were selected to provide a range in grain β‐glucan content. These lines, along with Penthouse and the hulled, malting variety Optic, were then malted, using four different steeping regimes, with samples kilned after 3, 4 and 5 days of germination. The longest steep regime provided samples with optimum modification after 5 days of germination. Samples from the other steep regimes were under‐modified to varying degrees. In particular, the steeps with a single immersion gave poorly modified samples with low extracts and alcohol yields. One line, with low grain β‐glucan, gave higher alcohol yields than either Penthouse or Optic, following a regime comprising two short immersions and a single air‐rest, but there was no clear association, within the lines, between β‐glucan content and malting properties. Copyright © 2012 The Institute of Brewing & Distilling     

Effects of malting on β‐glucanase and phytase activity in barley grain

The effects of malting on β‐glucan and phytate were investigated in one naked and one covered barley by a full factorial experiment with three factors (steeping temperature, moisture content and germination temperature) each with two levels. Analysis of total content of β‐glucan in the malted samples showed small changes after steeping at the high temperature (48 °C), while steeping at the lower temperature (15 °C) gave a significantly lower content. This trend was even stronger for β‐glucan unextractable at 38 °C. Analysis of the activity of β‐glucanase for the samples steeped at 15 °C showed a strong increase over the time of germination, while those steeped at 48 °C had a much slower development. The other two factors influenced the outcome to a small extent, mainly because the steeping temperature was the most important factor overall where any changes in β‐glucan and β‐glucanase were observed. When β‐glucan was extracted at 100 °C, a larger yield was obtained, and this was influenced by the steeping temperature in a much stronger way than for β‐glucan extracted at 38 °C. Determination of average molecular weight for β‐glucan extracted at 100 °C gave a lower value for samples steeped at 15 than at 48 °C. The design did not have any large effects on phytate degradation and phytase activity. However, it indicated that selective control of the enzymes might be possible, since phytase activity was barely affected by the parameters studied, while β‐glucanase was heavily affected. © 2002 Society of Chemical Industry     

THE EFFECT OF MODIFICATION PERIOD UPON THE ABILITY OF A MICRO-MALTING PROCEDURE TO SELECT BARLEYS FOR MALTING QUALITY

Using an established micro-malting method, designed to assess the malting quality of 20 g samples derived from a barley breeding programme, modification times of 4 and 5 days were found to give a large range of hot water extracts from genotypes of contrasting malting quality. Optimum modification of the grain occurred after 4 days.     

RAPID PREDICTION OF MALT HOT WATER EXTRACT BY NEAR INFRARED REFLECTANCE SPECTROSCOPY STUDIES ON BARLEY

In recent years there has been an increasing awareness of the need for rapid screening tests for malting quality in barley. An infrared reflectance instrument has been calibrated against malt hot water extract (HWE). Results suggest that this type of instrument can be used to estimate HWE on barley and that this might provide a suitable screening method for use in a breeding programme. Greater accuracy is achieved if separate calibrations are made for winter and spring barleys and the correlation coefficients with HWE were 0.70 (n = 168) and 0.82 (n = 134) respectively.     

A COMPUTER CONTROLLED MICROMALTER FOR ASSESSMENT OF THE MALTING POTENTIAL OF BARLEY CROSSBREDS

An automatic, computer-controlled micromalter with several advantages over current designs has been constructed. All operations are carried out in the one cabinet, and it is not necessary to intervene at any point during the malting process. The sample containers were constructed so that mechanical deculming of groups of ten large or fifteen small samples could be carried out in ten minutes. Initially, the capacity of the micro malter was 40 × 100 gm or 70 × 60 gm samples. These capacities were doubled by the use of longditudinal dividers slid into each canister, making the apparatus suitable for screening of samples submitted from the early generations of a breeding programme. The results obtained by malting 36 large and 60 small samples of the same variety; six replicates of six varieties; and subsamples of a bulk of a single variety in 37 subsequent runs all indicated that the instrument provided satisfactory separation and ranking between samples of differing malting qualities and grouped samples of similar malting qualities together.     

RELATIONSHIPS BETWEEN PEARLING RESISTANCES OF BARLEYS AND THE EXTRACT POTENTIAL OF THE SUBSEQUENT MALTS

A modified pearling instrument was used to determine the hardness of samples of barley and the results correlated with the extracts achieved by the malts made from those barleys. The influence of variety was such that the procedure could not be applied to selection of progeny from a breeding programme. However, the method could be used to accurately predict the malting potential of samples of varieties of malting barley if the relationship for the particular variety were known.