A substantial proportion of the UK economy is underpinned by the brewing and distilling industries, with nearly £3.5 billion in exports in 2010 for Scotch Whisky alone. The brewing industry supports the jobs of more than 600,000 people in the UK in agriculture, brewing, hospitality and the retail trade. Brewing and distilling in turn are heavily dependent on a supply of good malting quality barley. Such barley is produced in the UK from elite varieties that have been bred and selected specifically for the malting, brewing and distilling industries. Whilst the varieties that have and are being produced by breeding activity produce good levels of malt extract under optimum conditions, procuring supplies of barley grown under such conditions is not guaranteed and likely to become more difficult under the more varied climate envisaged by projected climate change scenarios. Under such conditions, some accepted malting varieties do not process efficiently during the malting process, increasing financial and environmental costs. An older variety, Maris Otter, has acquired the reputation of processing well under a range of different nitrogens, an attribute that is necessary to meet malt specifications for various brewing and distilling applications. We have confirmed this from the results of pilot brews (Figure 1) conducted by Campden BRI during the ‘Association Genetics of UK Elite Barley’ (AGOUEB) project. Maris Otter was first recommended in 1965 and was the result of a cross between a spring and winter malting varieties. Despite being outclassed by newer varieties on the recommended list, it is actively sought by craft brewers so that it still accounts for 4% of brewing malt purchases. Whilst all UK bred Institute of Brewing and Distilling (IBD) approved winter varieties have Maris Otter in their pedigree, maltsters and brewers feel that its processability has not been transmitted, especially to newer varieties. Given that malting quality is assessed on samples grown under low nitrogen conditions, it is perhaps not surprising that Maris Otter’s processability characteristics may have been lost due to genetic drift.
Our results clearly demonstrated that Maris Otter continues to process well even under high nitrogen conditions whereas samples of Pearl grown in the same high and low nitrogen environments were problematic and required raking for lautering (the process after mashing by which the liquid wort is run off from the residual spent grains) to continue, even under low nitrogen conditions. Under commercial conditions, this would consume more resources. Similar problems also occur amongst spring cultivars.
Problems in lautering largely arise when malt is poorly modified and cell wall components that have not been hydrolysed affect run off and can necessitate raking. The grain components likely to cause problems are principally protein, beta glucans, and arabinoxylans and it has been suggested that problems in the homogeneity of samples for grain nitrogen and beta glucan can lead to filtration problems (Palmer, 2000). Standard malt tests which give a mean value for all the grains within the sample do not detect this problem. For certain commercial varieties, a significant positive correlation has been found in a study of grain nitrogen levels in relation to grain texture, as measured by milling energy (Cowe et al., 1989), suggesting that varieties differ with regard to the effect of increased N levels on grain texture. The successful spring variety Triumph, which showed no correlation, subsequently featured in the pedigree of a large number of malting cultivars and it is likely that this lack of relationship will have been transmitted to its progeny. Chandra et al. (1999) showed differences in protein deposition between mealy (floury) and steely (vitreous) grained cultivars, as N levels increased. In mealy grain, protein levels increased in the embryo, whereas steely grain showed higher protein in the central endosperm. This may be one reason why Koliatsou and Palmer (2003) found mealy cultivars to release starch granules more readily when finely milled flour was suspended in ethanol. They detected this by measuring the turbidity of the suspension and also found a good correlation between their turbidity measurements and SKCS determinations of hardness. Additionally, mealy endosperms permit easier diffusion and more rapid water uptake during the steeping phase of malting. Most varieties need to reach around 42-46% moisture to ensure even germination (Bamforth and Barclay, 1993), so grains, within a sample, which do not achieve the required moisture content, may not modify properly. The malting process may thus magnify heterogeneity within grain samples from certain varieties. Variation in processing, over a range of nitrogen values, is a GxE interaction, so, where environments are likely to become more variable, the most effective approach may be to select for genetic factors that make varieties more stable across environments.
The major genes responsible for the synthesis and breakdown of cell wall components, together with some of the genes for protein accumulation and proteolysis, are well known and have been located on genetic maps and thus are potential candidate genes for processability. Whilst we do not rule out the possibility that processability differences may be the result of functional variants in one or more of the genes involved in the synthesis or breakdown of beta glucan and arabinoxylan, we believe that selection for good malting characters over time would have led to more or less complete fixation of the most suitable alleles in elite varieties, particularly in the spring genepool. Using our SNP maps of barley, we can identify small chromosomal regions containing genes affecting beta glucan and arabinoxylan synthesis and degradation and, using data generated during the AGOUEB project, survey the variation across a number of genotypes. For example, 70% of almost 550 elite barley lines have the same haplotype in the region on chromosome 1HL that contains Glb1, one of the major loci responsible for beta glucan hydrolysis during malting. Only five spring genotypes, none of which have any accepted malting quality, have an alternative haplotype. The next most frequent haplotype is found in 27% of the lines, all but one of which are winter. Whilst 6 out of 17 accepted UK winter malting genotypes are found in with this haplotype, varieties with reputed processing problems are found in both haplotype groups. Similar distributions can be found in the regions of other major genes associated with synthesis and breakdown of protein and cell wall components and our hypothesis is therefore that processability problems are due to more discrete differences in these characters and/or differences in the homogeneity of samples at higher grain nitrogen contents.
Other results from AGOUEB have demonstrated that we can identify genomic regions associated with malting parameters such as wort beta-glucan, wort viscosity, friability and homogeneity, which reflect some aspects of processability.
These results show that most of the associations that we have detected are crop specific, although there is some evidence of common regions detected in spring and winter barley on chromosomes 3H and 4H. Our findings are however, based upon historical micro-malting data gathered from sites specifically selected for acceptable grain nitrogen content and not therefore likely to present an accurate picture of the problems likely to be experienced by maltsters in selecting lots for commercial malting. Furthermore, none of the varieties have been grown in trials together and so we had no direct comparison of lines grown in the 1990s with lines grown in the 2000s.
The genotypic data from the elite spring and winter barley lines is an existing resource that can efficiently be combined with new phenotypic data to identify the genomic regions affecting malt processability. In addition, we have transcriptomic resources at the James Hutton Institute that can be used to examine gene expression differences between good and poor processing lines.
Whilst many barley genotypes can malt adequately under low nitrogen conditions, it is the hallmark of a good malting genotype that it maintains its quality profile over a wide range of grain nitrogen states. Our strategy is therefore designed to highlight genotypes that still process well under a higher nitrogen condition as better malting varieties maintain relatively higher levels of extract as nitrogen levels increase (Lloyd, 1982). We have therefore grown trials of elite winter and spring barley lines under malting and feed nitrogen management regimes to produce malt samples from each for analysis of malting characters. We are combining the malting phenotypes with the existing genotypic data in genome wide association analyses to identify genetic regions, markers and potential candidate genes that affect the stability of the malting parameters across these markedly different environments. The markers can then be used in research and breeding to improve the overall quality of UK malting barley for domestic and export markets.
For further information on this project please contact Bill Thomas (email@example.com) from the James Hutton Institute.