Malt and Grains Session
Aaron Macleod, Canadian Grain Commission, Winnipeg, Manitoba, Canada
Co-author(s): John O’Donovan and Kelly Turkington, Agriculture and Agri-Food Canada, Lacombe, AB, Canada; Michael Edney, Canadian Grain Commission, Winnipeg, MB, Canada
ABSTRACT: The fermentability of malt wort is dependent on providing an adequate supply of the amino acids necessary for yeast metabolism. In addition to supplying the required amounts of total free amino nitrogen, the relative concentrations of individual amino acids must also be considered given their differences in absorption and use by the yeast. It is unclear how amino acid composition of wort is affected by factors such as cultivar, nitrogen application, and growing environment; factors that are all known to have significant effects on grain protein levels. In the present study, five Canadian malting barley varieties (AC Metcalfe, Major, CDC Meredith, Bentley, and Merit 57) were grown with different nitrogen application rates (0, 30, 60, 90, and 120 kg/ha) producing grain with a range of protein levels. The amino acid composition of the barley and resulting malt worts was determined using ultra performance liquid chromatography (UPLC). The proportions of glutamic acid, proline, and phenylalanine in barley grain were positively correlated with protein content, whereas the levels of other amino acids showed a negative correlation with protein content. This relationship was consistent among all varieties. While total levels of free amino nitrogen in wort generally increased with barley protein, the proportions of most essential amino acids such as histidine, lysine, and leucine, which can not be synthesized by yeast, were negatively correlated with grain protein. One notable exception was arginine, for which concentrations increased. Variety also had a significant effect on the amino acid profile in the grain and wort. Levels of amino acids in the barley grain of low protein varieties such as Bentley, CDC Meredith, and Merit 57 were consistent with their protein content. However, this relationship was not maintained in the resulting worts, likely as a result of protease activity in the mash. Different brewing practices require malts with various protein, amino acid, and enzyme levels depending on gravity and levels of adjunct used. A better understanding of the relationship between these factors will aid in the development of new varieties to meet the needs of the modern brewer.
Aaron MacLeod is a chemist in the Applied Barley Research unit of the Canadian Grain Commission Grain Research Laboratory. The unit provides quality assurance for malting barley grown in western Canada and conducts research on factors affecting malting barley quality and quality measurement methods. Aaron earned a B.S. degree in chemistry from the University of Western Ontario. An active ASBC member since 2008, Aaron has participated in the collaborative study of numerous new methods and is currently serving on the ASBC Technical Committee.