Investigation of a ribes off-flavour in beer.

Cosser, K.B., Murray, J.P. and Holzapfel, C.W.

Abstract
An off flavour detected for a few months in beers and then disappeared, was considered by taste panel testing to be ribes. A thorough investigation of brewing liquor, raw materials, filtration material, boiler water treatments and chemicals used for cleaning and sterilisation, revealed that the off flavour was derived from the malt and was subsequently traced to the germinating barley being caused by contamination from mesityl oxide, an impurity in paint used on the maltings. Laboratory experiments showed that mesityl oxide reacted with hydrogen sulphide to form a compound which was revealed by gas chromatography and mass spectrometry to be 4 methyl 4 mercapto pentan 2 one. Even at very low concentrations this compound shows the characteristic odour of ribes. Earlier investigations in a meat processing plant which had also undergone painting had also revealed that a ribes off flavour which had appeared was due to mesityl oxide impurity in the paint used. It is evident from the results that constant watch should be kept for the appearance of airborne contaminants which can affect flavour at extremely low concentrations.
Keywords: air beer catty flavour malting off flavour paint pollution