AARON MACLEOD (1), Bill Legge (2), Rob McCaig (3), Michael Edney (1)
(1) Canadian Grain Commission, Winnipeg, MB, Canada; (2) Agriculture and
AgriFood Canada, Brandon, MB, Canada; (3) Canadian Malting Barley
Technical Centre, Winnipeg, MB, Canada
Minerals are essential for continuous yeast growth, a requirement for
efficient fermentation, and their requirements increase when fermenting
worts with high gravity or high levels of adjunct. Availability of
minerals can be reduced in barley by phytic acid, or phytate, a
chelating agent present in barley, which is involved in binding and
precipitation of minerals. Low-phytate barley was originally developed
to increase nutritional availability of minerals for humans and farm
animals but potential benefits for brewing led to development of a
doubled-haploid population from the cross between AC Metcalfe and a
reduced-phytate barley mutant. This study determined the impact of
brewing with the low-phytate barley malts on wort mineral availability
and fermentation performance. Barley from normal and low-phytate
doubled-haploid bulks, based on bulk segregant analysis, and parents
were grown in multiple locations during each of two growing seasons.
Malts made from regular and reduced-phytate barley were brewed in a 3-hL
brewery using maltose syrup as adjunct, to bring the starting gravity
to 14°P. The worts and resulting beers were analyzed for minerals using
atomic absorption spectroscopy. Acidity and pH were also measured to
determine the effect of changes in free phosphate ions on buffering
capacity of wort. Average levels of zinc increased from 0.1 ppm in
normal worts to 0.3 ppm in low-phytate worts. Magnesium levels also
increased on average from 125 to 135 ppm. Zinc and magnesium are both
necessary for yeast growth, and can be limiting to fermentation. While
no differences were found in the levels of copper between low- and
normal-phytate worts, iron levels did increase from 0.1 to 0.3 ppm.
Elevated levels of iron can have a negative effect on flavor and foam
stability. Acidity and buffering capacity of worts were unaffected by
the low-phytate trait, despite the anticipated increase in free
phosphate ions. Increased fermentation efficiency was demonstrated in
the pilot brewery and also in laboratory-scale testing. Adjunct
fermentations with low-phytate malt used more zinc, and achieved better
attenuation than malt with normal phytate levels. Low-phytate lines are
being pursued for release as commercial malt barley varieties.
Aaron MacLeod joined the Canadian Grain Commission in 2005 and is
currently a chemist in the Applied Barley Unit of the 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 measurement methods. Aaron holds a B.S. degree in
chemistry from the University of Western Ontario and has been a member
of ASBC since 2008. He has participated in the collaborative study of
numerous methods and is currently the chair of two technical
subcommittees. Aaron is also the secretary of the Canadian Prairie
Section of AACC International.
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