Effect of carbonyl sulphide (COS), ethyl formate (EF) and carbon disulphide (CS2) on the malting quality of barley and the flavour profile of beer

Abstract

New fumigants are needed to control grain insects because methyl bromide is being phased out as an ozone-depleting substance under the Montreal Protocol and because resistance to phosphine is increasing. Alternative fumigants also provide one strategy to manage resistance. To assess the effect of candidate fumigants on barley quality, malting and brewing trials were conducted with malting barley (Schooner), 9.4% moisture content, fumigated with carbonyl sulphide (COS), ethyl formate (EF) and carbon disulphide (CS2) at concentrations of 20, 90 and 36 mg/L respectively for 7 days at 20°C in riveted steel silos containing 33 t of barley. The appropriate industry body, the Malting and Brewing Industry Barley Technical Committee (MBIBTC) set the quality parameters to be evaluated and allocated work to the appropriate quality laboratories. Germination of fumigated barley was not affected by the fumigants. Residues of COS, EF and CS2 in outloading barley samples were 0.085 ± 0.0052, 0.4 ± 0.1 and 2.22 ± 0.07 mg/kg respectively, which were below the experimental permits of maximum residue levels (MRL). Residues of COS, EF and CS2 in malt, wort and beer were indistinguishable from those in unfumigated (or non-fumigated) barley. Ethyl formate and CS2 affected wort in increasing the apparent attenuation limit (AAL) and CS2 affected barley colour. Sulphur volatiles in the trial beer made from EF and CS2 (unlike COS) fumigated barley decreased significantly. Beer from COS, EF and CS2 fumigated barley had a somewhat higher 24-hour chill haze level (0.62-0.84) than beer from the untreated barley (0.53). The total alcohols and isoamyl acetate increased in beer made from EF fumigated barley. Carbonyl sulphide, EF and CS2, however, had no effect on beer flavour or quality. © 2011 The Institute of Brewing & Distilling.