REQUIREMENTS FOR INNOVATORY RESEARCH IN SUPPORT OF MALTING AND BREWING

The balance of research within the malting and brewing industries has been assessed using the studies reported at the 18th and 19th EBC Congresses. These studies have been arranged in four categories depending upon the innovatory/supportative nature of the work. The innovatory proportion is judged to be 25% and it is argued that this value, while highly respectable, will need to be increased because of the maturity achieved by malting and brewing processes since the frenetic changes of a decade or so ago. Some areas requiring innovatory effort have been identified. Attention is drawn to the fact that innovatory research involving the whole malting/brewing process is largely absent and that it is this area that presents the largest challenge and the greatest rewards.     

FILTRATION IN BREWING—A REVIEW*

The processes involved In wort separation are discussed in terms of the underlying mathematical principles as exemplified by the Carman-Kozeny equation, which is applicable to cake filtration, the Moncrieff equation, which is relevant to sparging, and Stokes' Law, which is concerned with settling of particles in regions of viscous flow. The behaviour of small-scale mashes of different types is illustrated photographically. Beer clarification, polishing and sterilization are discussed as further examples of filtration in brewing.     

THE INDUSTRIAL USE OF GIBBERELLIC ACID AND ITS SCIENTIFIC BASIS—A REVIEW

Over the last 15 years numerous studies, both fundamental and applied, have ensured for gibberellic acid (GA₃) a firm place in the routine commercial malting of barley and the production of fruits. A large number of the thirty-eight gibberellins so far characterized occur naturally, e.g. gibberellic acid in germinating barley. Commercial application of gibberellic acid during malting therefore supplements the natural endogenous levels of this hormone. Small additions of gibberellic acid accelerate the production and release into the endosperm of enzymes which degrade the hemicellulosic-protein-starch complex into essential brewing materials such as sugar, peptides and amino acids. A combination of abrasion with gibberellic acid application results in further acceleration of the malting process. Abrasion of the pericarp at the distal end of barley grains allows them, in the presence of normal levels of gibberellic acid, to malt simultaneously from both their embryo and non-embryo ends: malting time is drastically reduced and soluble malt extract is increased. In spite of the widespread industrial use of gibberellic acid, the cellular mechanisms through which gibberellic acid elicits its various actions on plant growth and development are not yet known; however, with barley aleurone cells gibberellic acid can induce drastic reorganization and synthesis of subcellular organelles. The net result of gibberellin treatment may be vigorous production and secretion of hydrolytic enzymes or, in other circumstances a rapid acceleration of growth and development. It is as yet unknown whether these apparently diverse expressions of gibberellin action have a similar biochemical basis.     

THE CHEMISTRY OF NITROSAMINE FORMATION: RELEVANCE TO MALTING AND BREWING

This paper reviews the chemistry of nitrosamine formation with special reference to malting and brewing. Whilst the main emphasis is on the formation of nitrosodimethylamine (NDMA), the chemistry is also related to the formation of other nitrosamines and certain other nitrocompounds. It seems likely that in malting and brewing the only important source of the nitroso group is the mixture of oxides of nitrogen (NO_x) in the hot air in contact with malt during kilning. Under normal commercial conditions there appears to be little if any formation of nitrosamines at other stages of malting or brewing. It is suggested that much of the nitrosation is due to NO_x which exists temporarily in the form of nitrogen trioxide (N₂O₃) and nitrogen tetroxide (N₂O₄) as it dissolves in water in the moist malt or in malt lipids. The dissolved NO_x subsequently reaches equilibrium with nitrite and nitrate ions formed from it. The origin of the dimethylamine portion of the NDMA is still not clear. The most likely sources are free DMA, gramine and hordenine, all of which are produced in germinating barley. On balance it seems that hordenine is the most important source of NDMA in the malt at the end of kilning. The reasons for the low yield of nitrosamines from the precursors and NO_x present during kilning are discussed and related to the formation of other nitroso- and nitro-compounds. The occurrence of competing reactions which reduce nitrosamine formation is also described.     

AUTOMATION OF BREWING ANALYSES—A REVIEW

Automated methods of analysis available to the brewing industry for in-line analysis, quality control and assurance purposes are reviewed.     

DIMETHYL SULPHIDE FORMATION IN MALT—EFFECT OF MALTING CONDITIONS

The dimethyl sulphide (DMS) content of kilned malt, and, presumably, the level of precursor in green malt, is significantly affected by malting conditions. Increasing proteolysis favours increased DMS formation in the malt, particularly when induced by higher germination temperatures. The additives gibberellic acid and potassium bromate have opposing effects, some increase being caused by the former and significant reduction being achieved by the latter.     

HOP CHEMISTRY IN RELATION TO BREWING—A REVIEW*

The synthesis of hop components of brewing value—viz., essential oils and α and β acids—from fundamental structural units such as acetic acid and isoprene, is outlined. Quantitative relationships between essential oils and resin acids are shown to result from common steps in the synthetic pathways of the two classes of compound. Changes in α and β acids resulting from oxidation and from boiling are discussed. Bitter values obtained by adding hops on the basis of polarimetric analysis are contrasted with those found in beer bittered at a constant hop rate, and thin layer chromatography is shown to afford a reproducible means of analysing beer for different hop constituents.     

HEAT SENSITIVITY,OPTIMUM pH AND CHANGES IN ACTIVITY OF SORGHUM PEROXIDASE DURING MALTING AND MASHING

Peroxidase activity was demonstrated in dry and germinating sorghum seeds. The specific activity increased about 14-fold during malting for a 96-hour period. On the average about 41% of peroxidase activity was located in the endosperm, and the remaining 56% in the acrospire and rootlet of sorghum malt. The crude enzyme extract retained 77%, 17.5% and 7.6% of activity after heating at 60°, 70° and 80°C, respectively. More than 50% of the peroxidase activity in the finished malt survived mashing at 65°C. Optimum activity was recorded at pH 5.5 which falls within the observed pH range of sorghum worts. The level of residual peroxidase activity in the wort differed with sorghum species.     

HORDEIN IN BARLEY AND MALT—A REVIEW

The chemical nature of hordein and current methods of extraction and fractionation are reviewed. The importance of hordein in identifying barley varieties and in predicting and assessing malting performance is discussed. Proteolytic breakdown of hordein during malting and mashing is summarized and the composition of hordein from barley, malt and spent grains is compared.     

THE PROTEIN RESERVES OF THE BARLEY GRAIN AND THEIR DEGRADATION DURING MALTING AND BREWING

The hordeins of barley are the main components of the grain protein, comprising B (sulphur rich), C (sulphur poor) and D (high relative molecular mass) species. A gel fraction can be isolated that consists of the D and part of the B hordein. Other important components of the reserve protein are β-amylase, protein Z and enzyme inhibitors as well as endosperm cell wall protein and protein associated with the starch granules. Degradation of protein is mediated by peptidase enzymes, most important of which are the endopeptidases and the exopeptidases; the latter having specificity for the carboxy- or amino-terminal region of a polypeptide chain. A very high activity of carboxypeptidase develops in the germinating barley grain. Five carboxypeptidases have been identified in malt and three fully characterized. Several endopeptidases have been identified, which have optimum activity close to pH 5.0 (that of the starchy endosperm) and studies with active site inhibitors suggest that sulphydryl dependent species are the most important. However, only limited use has been made of hordein as a substrate in the measurement of peptidase activity in malt. Lack of a complete understanding on the peptidases and their regulation in the germinating barley is a major limiting factor in the knowledge on the mobilization of the protein reserves during malting and mashing. Both de novo synthesis and activation of the peptidases have been demonstrated and the hormones gibberellic acid and abscisic acid appear to have a regulatory role. A controlled modification of the protein reserve is required so that there is an appropriate supply of amino acids for the brewers yeast but retention of proteins important in the desirable foaming component of beer. It is also important that proteins which can interfere in the final stages of brewing, e.g. those with chill haze forming potential, are broken down. An early hydrolysis is required of cell wall proteins and those proteins intimately associated with the starch granules.     

STARCH HYDROLYSIS IN MALTING AND MASHING

Starch hydrolysis in malting and mashing processes was studied by gel chromatography on Sepharose Cl 4B. The final molecular weight distribution of starch components in malt differs from those in barley. During malting a molecular weight fraction close to the void volume appears as an intermediate product. Minor differences in starch hydrolysis in mashes with different malts is obtained, though the final dextrin composition of the worts is similar.     

DIFFERENCES IN MALTING PERFORMANCE BETWEEN BARLEYS GROWN IN SPAIN AND SCOTLAND

Two barley genotypes were grown, in 2 seasons, at sites in both Scotland and Spain. The development of enzyme levels and endosperm modification were assayed, over the final 3 days of malting. Spanish grown samples demonstrated faster and more extensive synthesis of both α-amylase and β-glucanase, more rapid cell wall modification and a greater reduction in milling energy during malting than Scottish grown samples. Malt milling energy was strongly associated with cell wall breakdown, which was a limiting step in modification of Scottish, but not Spanish, grown samples. Extract levels were not related to α-amylase activity, but Kolbach index exhibited an association with extract at both sites.     

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.     

MEASUREMENT OF CARBOHYDRATES IN WORT AND BEER—A REVIEW

Methods are reviewed for measuring total wort and beer carbohydrate and carbohydrate fractions, such as dextrins, oligosaccharides, fermentable sugars, β-glucans, total fructose and fructosans, pentose and pentosans. The methods are conveniently classified under the following headings: reductometry, colorimetry, enzymic procedures, automated analyses, paper and column chromatography, thin layer chromatography, gas liquid chromatography and high performance liquid chromatography. Techniques involving chromatography are particularly useful for separating and estimating individual sugars.     

CHANGES IN ACTIVITY OF SORGHUM LIPASE DURING MALTING AND MASHING

Lipase activity was monitored during malting and mashing of sorghum grains. All three sorghum varieties contained detectable lipase activity in the ungerminated form. Lipase activity changed only slightly during steeping for 24 hours but increased several fold in the course of germination. Between 24% and 60% of the lipase activity of the green malt was retained after kilning at 48°C but no activity was detected in the wort after mashing at 65°C. About 68% of the lipase activity of 72 hours old malt was detected in the plumule, while 29% and 3% were detected in the endosperm and radicle, respectively. Optimum activity was observed at pH 7.0.     

ASSESSMENT OF MODIFICATION PATTERNS IN MALTING BARLEYS

Three cultivars of diverse melting quality were melted end samples taken daily between 2 end 7 days germination. Over this period a linear relationship wee observed in all 3 cultivars, between cell well modification, measured by loss of calcofluor fluorescence, and both wort nitrogen content end loss of milling energy. Differences in the slopes of regression lines suggested variation in patterns of modification, with very rapid proteolysis in Triumph, but a time leg between cell wall modification and degradation of the protein matrix in Koru. These predicted patterns were confirmed by Scanning Electron Micrographs of endosperms from germinated grains.     

EFFLUENTS FROM MALTING AND BREWING*

Following a general discussion of the effects of different types of industrial waste on the waters receiving these wastes, and a survey of methods available for assessing the polluting strength of effluents (e.g. Biochemical Oxygen Demand and Chemical Oxygen Demand) analyses are given of the occurrence and nature of specified malting and brewery effluents. Methods of treatment, including the use of bacteria beds and of activated sludge are described and evaluated and estimates of costs of treatment and disposal are suggested.     

MODIFICATION IN MALTING BARLEY

The patterns and degrees of modification found in the same grains, by successively applying the Calcofluor and Methylene Blue techniques, while similar were not identical. The Methylene Blue technique over-estimated modification in short-grown grains because the dye spread around the sheaf-cells, into cracks, and into mealy regions of the starchy endosperm. Calcofluor gave slightly higher modification scores in more completely modified grains. Reasons for the discrepancies are suggested. Differences in staining indicate that the nature of endosperm degradation caused by enzymes from the scutellum is different to that caused by enzymes from the aleurone layer. Sometimes patches of unmodified endosperm tissue occured adjacent to the aleurone layer between the zones of modification caused by the two groups of enzymes. Modification sometimes extended around cracks in the starchy endosperm. Various patterns of modification were detected. Other patterns indicate that the aleurone sometimes more or less fails to generate wall-degrading enzymes. Both light and scanning-electron microscopy indicated that cell walls of the starchy endosperm become fragmentary, and were totally degraded in completely modified regions.     

NITROSAMINES IN MALT AND BEER

A brief account is given of the co-operation between the malting and brewing industries and the Ministry of Agriculture, Fisheries and Food in solving the NDMA problem in beer. The formation and removal of NDMA during processing is discussed with emphasis on methods used commercially to limit NDMA in the products.