DETECTION OF THE SULPHURING OF HOPS DURING KILNING AND CULTIVATION

Abstract

Since brewing companies are now reluctant to accept hops treated with sulphur during kilning and cultivation, methods have been developed for detecting such contamination. In the procedure for estimating residual elemental sulphur, milled hops are continuously extracted with cyclohexane and dissolved sulphur is deposited on copper gauze as copper (I) sulphide. Hydrogen sulphide is then formed by the addition of hydrochloric acid and is absorbed in potassium hydroxide solution. The dissolved sulphide is finally estimated by titration using p-chloromercuribenzoic acid and diphenylthiocarbazone as indicator. The modified Monier Williams procedure, as recommended by the Institute of Brewing for estimating sulphur dioxide in beer, has been adapted for analysing hops. This provides a convenient technique for determining whether or not hops have been treated with sulphur or sulphur dioxide during kilning. The sulphur dioxide content of fresh hops treated at normal rates is of the order of 800 mg/kg. A number of samples of hops from the 1980 crop have been analysed and the levels of sulphur dioxide were found to be within the range 1 to 80 mg/kg. It is likely that these low levels are the result of using fuel oils, which contain variable amounts of sulphur, to dry the hops.