Sulphur compounds derived from the essential oil of hops can give rise to off-flavours in beer. A number of compounds whose formation is accelerated by heating have been identified and flavour thresholds established. To ensure sound 'hop-character', i.e. flavour due to the essential oil, heat processes should be avoided, for example by distillation under vacuum at low temperature or by using extracts made with liquid carbon dioxide. Dimethyl sulphide, a desirable flavour constituent of many lagers, is formed from a precursor which is produced during the germination of barley. However, it has now been shown that in certain conditions of fermentation, dimethyl sulphide can be produced from an alternative source. The fermentation of high gravity worts made with large proportions of adjunct can be accelerated by supplementing the supplies of amino acids and oxygen. Increase in the supply of amino nitrogen increases yeast-growth without affecting the rate or extent of fermentation. The combination of nitrogen and oxygen speeds and extends fermentation but with a disproportionately high increase in yeast growth.
Keywords: attenuation brewing dimethylsulphide fermentation flavour hops sulphur compound survey terpene