Cereal grains are sometimes sprayed with oil during handling in order to minimize dust levels for safety reasons, but in the case of malting barley there has been some concern about the possible adverse effects on beer quality of any residual oil remaining on the barley during malting and brewing. Following on from a previous study by two of the present authors (Schwarz and Barr) (J. Am. Soc. Brew. Chem., 1993, 51(4), 152-155) on the fate of residual traces of light mineral oil used for that purpose, a further investigation into the effects of using vegetable oil (in this case soybean oil) was carried out. A commercial soybean oil, to which a solution of triheptadecenoin in hexane was added as a chemical marker, was sprayed over half of a 12 kg batch of barley, the other half batch being left untreated as a control. Both half batches were malted and three 800 g sub batches from each half were microbrewed. Samples of raw grain, malted grain, rootlets, spent grains, wort, trub/spent hops, cropped yeast and beer were analysed for total fatty acids by extraction, hydrolysis, methylation and gas chromatography/flame ionization detection, while the chemical marker was determined in the methylated hydrolysed extracts of the samples by gas chromatography/mass spectroscopy. It was found that the fatty acid analysis could not detect the addition of soybean oil, but the chemical marker (a form of 10-heptadecenoic acid, which is a fatty acid but does not occur naturally in either soybean oil or barley) showed that about 62% of the oil applied to the barley was lost during malting (apparently mostly by being washed off during steeping), and about 98% of the oil remaining on the malt was found in the spent grains after mashing. No traces of the marker were found in wort or beer, or in by-products other than malt rootlets and spent grains, indicating that the oil did not pass into the wort or did so only in trace quantities too small to be detected. However, it is pointed out that vegetable oils are subject to oxidation, which causes them to become rancid, and that lipid oxidation products can cause perceptible off flavours in beer even at concentrations as low as 1 ppb. It is therefore recommended that any oils used for dust control in malting barley handling systems should be stabilized against oxidation.
Keywords : analysis barley beer by-product malt oil spent grains vegetable wort