Understanding the components of specific weight in barley grains: opportunities for improving grain quality and processing efficiency.
Item statusRestricted Access
Embargo end date15/07/2021
Hoyle, Aaron Benjamin Sinclair
Spring barley is the primary cereal crop grown in Scotland, 35% of the crop is used for malting and 55% for animal feed. There is a clear distinction between barley destined for malting or feed, this is a result of the higher quality grain demanded for malting and consequently a premium is paid for this. For example, in the UK during September 2018 malting barley reached prices of £46/t more than that of feed barley. Quality requirements for malting barley include: germination rate, per cent admixture, nitrogen levels, cultivar, moisture content, uniformity, skinning level, disease/weathering damage and specific weight (SW). Therefore different agronomic approaches are taken when a grower is striving for either malting or feed barley. The majority of these malting barley quality requirements are well understood, SW is well established however its impact on malting outputs or efficiency are not well understood. Specific weight is one of the longest standing measures of grain quality for cereals and oilseeds, it is a measure of the weight of grain per unit volume and is reported in kilograms per hectolitre (kg hl-1 ). An increased SW is thought to be beneficial for malt output. The aim of this thesis is to enhance the understanding of SW as a measure of grain quality, and to establish what aspects of barley grain determine this measure. Following establishing these grain traits, the aim is then to relate these to the malting process and outputs, to understand how SW influences malting. Firstly, SW has been demonstrated to have two components: grain density and packing efficiency. This is a key part of the thesis, because both components can change independently. Different grain parameters influence each of the components, therefore both need to be considered together when investigating SW differences or similarities between samples. The packing efficiency and grain density of nine spring barley cultivars was investigated, this demonstrated that grain density contributed 48.5% to the variation in SW and packing efficiency 36.5% to the variation in SW. It was hypothesised that the packing efficiency of grains was primarily influenced by grain morphometrics, and grain density influenced by composition. Investigating how composition changes with grain density was investigated by first stratifying grains by density, resulting in groups of grains with different densities. Compositional analyses were then carried out on these groups which showed that grain nitrogen level and the proportional volume of starch B-type granules contributed 47% to the observed variation in grain density. Specific weight is also known to be affected by growing conditions, with year to year variation observed. Such year-on-year variations might be a result of changing climatic conditions between years, therefore the effect of a moderate, but prolonged water stress was investigated under glasshouse conditions. Plant development was altered by the stress, but SW was maintained through compensatory mechanisms. To investigate how changes in SW affect malt quality parameters, SW was manipulated through selection for different grain size and weights. Specific weight was shown to be strongly correlated with the predicted spirit yield and hot water extract of the malt. These are two fundamental measures of malt quality. Grain density also correlated with these two measures, but packing efficiency of the grains did not. This indicates that it is grain density rather than the packing efficiency of the grain that is the beneficial component of SW for malting. Therefore if breeding of elite malting cultivars is continued to enhance malt quality through increasing SW, this should be done so through increasing the grain density component rather than packing efficiency.