A Colorimetric Procedure for the Measurement of Dimethyl Sulfide in Water, Wort, and Beer

Abstract

A colorimetric method is presented for the quantitative determination of dimethyl sulfide (DMS) in water, wort, and beer. The method is based on the formation of a complex between DMS and sodium nitroprusside. The DMS-sodium nitroprusside complex which is formed under alkaline conditions turns pink when the solution is acidified. The pink complex has an absorption maximum at 520 nm. Details of the procedure for the determination of DMS are presented in this paper, along with optimum conditions for its extraction from various media as well as for color development and measurement. The method is reproducible (standard deviation = 3.7 μg/1), accurate (±2%), and rapid (32 analyses may be performed in 8 hr). DMS found in commercial beers ranges from 30 to 160 μg/1., with most beers falling in the 40 to 70 μg/1. range. Fora given brand of beer, the DMS concentration appeared to remain fairly constant, indicating that its level is characteristic of the brewing materials and process conditions. Dimethyl sulfide increases in beer upon storage under warm conditions, the extent of increase being dependent on the length of storage and the temperature. Heat treatment of wort brings about an increase in the level of DMS. Microbial contamination of wort also results in appreciable increases in the concentration of DMS.