O-5
The behaviour of the grain protectant pirimiphos-methyl in malting. Pirimiphos-methyl (P-M) is an organophosphorus insecticide which has been
used for many years to treat grain in order to protect it from insect attack
during storage. Pirimiphos-methyl and other structurally similar chemicals such
as chlorpyrifos-methyl are registered in several countries, and have been used
since the late 1970s on malting barley. Although there are some published
studies addressing the degradation of residues in grain during storage, much
less is known about the behaviour of these chemicals during processing. The aim
of the work described in this paper was to ascertain the effect of the malting
process on residues in barley and malt. Malting barley was treated with
pirimiphos-methyl in order to yield grain with residues close to the legal limit
for barley in the European Union. Treated barley was malted on a pilot scale
using both ale and lager regimes. Samples of steep water, roots and finished
malt as well as samples of green malt taken during processing were analysed for
pirimiphos-methyl residues. Residues were identified and quantified by GC-MS
with selective ion monitoring. After steeping, the moist barley at casting
contained only slightly less P-M (on a dry weight basis) than did the starting
barley. Levels of P-M also remained fairly constant during germination, with no
evidence of any degradation due to grain metabolism, except possibly on the last
day of germination. Substantial losses of P-M were observed during kilning. The
roots were relatively high in P-M, but de-rooting had a relatively small effect
on the total amount of P-M in the malt batch, since the total weight of roots
was negligible. The results indicate that less than 20% of the insecticide
present on the initial grain survives the malting process. Both batches of
barley malted satisfactorily. Analytical data for standard malt quality
parameters were as expected for the variety and conditions used and were within
commercial specifications. There was no evidence of any deleterious effects on
malt quality due to pirimiphos-methyl treatment.
Denise Baxter joined BRI in 1972 from Edinburgh University. After
researching into several aspects of malting biochemistry and physiology, Denise
assumed responsibility for Food Safety matters in 1986. This post involves
initiating and managing a programme of research and monitoring relating to food
safety and health issues for the Brewing Industry. The Food Safety team which
Denise heads at BRI also provides advice and consultancy for Member Companies.
As Head of Food Safety, Denise is a Member of several malting and brewing
industry committees.
E. DENISE BAXTER, Christopher D. Booer, and Ian R. Slaiding. Brewing Research
International, Nutfield, Surrey, UK.