Abstract
The use of elemental sulphur and sulphur containing pesticides on hops, on the bine, has been shown to give rise to increased levels of organo-sulphur compounds in the essential oil. These compounds have extremely detrimental effects on the flavour and aroma of finished ales and lagers. It is therefore of importance to understand the occurence, nature and chemistry of these compounds so as to improve control of the husbandry and use of hops for brewing purposes. Two organo-sulphur compounds already identified in hops, 4,5-epithio-caryophyllene and 1,2-epithiohumulene, have higher flavour thresholds in comparison to other organo-sulphur compounds. In order to discover if these may be converted to more flavour potent thiols in the brewing process it was necessary to synthesise these in quantity so as to study their chemistry. These could not be prepared in high yield but micro scale studies indicated that they are stable to mild hydrolysis and are desulphurised by oxygen at 100°C. A number of novel tricyclic derivatives were, however, isolated, from preparations to synthesise the episulphides and these were characterised by chemical and/or physical methods. Myrcene, a monoterpene, has been shown to react with sulphur under mild conditions to give a number of sulphur containing adducts, four of which occur in hop oils. Two of these, 5-(4-methyl-3-pentenyl)-1,2,3-trithiacyclohept-5-ene and 6-(4-methy1-3-pentenyl)-1,2,3,4-tetrathiacyclooct-6-ene have been positively identified by synthesis. A third compound from the myrcene/sulphur reaction has been identified, on the basis of accurate mass measurements and g. c. retention data, to be 3-(4-methyl-3-pentenyl)-thiolene. A number of other novel compounds were prepared in attempts to synthesise this cyclic monosulphide. Of major importance in the brewing process are the hop resins humulone and colupulone as these give rise to the characteristic bitterness of beer. These compounds, and two analogous compounds, were shown to be completely inert towards elemental sulphur under mild conditions.