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sulphide in wort. The higher concentrations were reported to be associated with elevated levels of copper. This is surprising in that addition of copper ions to beer was used as a method of reducing hydrogen sulphide concentration in beer by encouraging the formation of insoluble copper sulphide.

Organic constituents of worts include the sulphur-containing amino acids, methionine, cystine and cysteine. In addition, there are other sulphur-containing biochemicals such as glutathione, thiamine and free and esterified coenzyme A. Cooled wort contains dimethyl sulphide, its precursor, S-methylmethionine and the related dimethylsulphoxide. The proportion of each depends on the variety of malt used, the duration of the copper boil and the conditions employed in wort cooling. Anness (1981) suggested that pitching worts (ll°Plato) usually contain 200-700 (igl 1 dimethyl sulphoxide and 30-50 (igl 1 each of S-methylmethionine and dimethylsul-phide. However, much variation is possible depending on the combination of effects as discussed above.

Of the many compounds identified in hop oils, about 30 contain sulphur (Seaton et al., 1981). These include dimethyl sulphide, other polymethyl sulphides and several thiolesters, for example, methylthioacetate and ethylthioacetate. In addition, treatment of hops with elemental sulphur can lead to reactions with hop oil constituents to form episulphides such as 1,2-epithiohumelene, 4,5-epithiohumulene, 4,5-epithiocaryophyllene and myrcene disulphide. Many of these sulphur-containing hop components have unpleasant flavours and aromas (Soltoft, 1988). The relative concentrations of these, which persist in pitching wort, are dependent on the varieties of hops, or derived products, which are used and the conditions of wort production.

2.4.6 Minerals

Minerals in hopped wort derive mainly from brewing water although significant concentrations also arise from the other raw materials. More concentrated worts will inevitably contain a higher proportion of minerals derived from malt and the other sources of extract used. Beers made with hard water such as UK pale ales have worts which contain higher levels of sulphate and other ions compared to

Pilsener-type lagers which use very soft water for wort production. In the case of the latter beers, the bulk of the minerals in worts are derived from malt and hops. The increasingly common practice of using brewing water which has been completely de-mineralised and then dosed with a cocktail of salts considered to be appropriate for a particular beer style will tend towards a simpler ionic composition compared to worts made with relatively untreated bore-hole waters. Thus, there may be much variation in the mineral composition of individual worts. Mandl (1974) gave average mineral values for 12°Plato wort. These are reproduced in Table 2.13.

Table 2.13 Mineral composition of a 12% solids hopped wort (from Mandl, 1974).

Component

Concentration (mg 1 ')

Potassium

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