The Measurement of Sulfur-Containing Aroma Compounds in Samples from Production-Scale Brewery Operations

Abstract

A method employing solid-phase microextraction followed by gas chromatography and detection by chemiluminescence has been used to measure sulfur-containing volatile substances in a range of beers and brewery process samples. Commercial beers were very similar in the types of sulfur-containing molecules contained. All beers tested, including ales, featured high levels of dimethyl sulfide, as well as methanethiol and S-methyl thioacetate. Only one beer was free from sulfur dioxide and only one was devoid of dimethyl disulfide. None of the beers contained detectable levels of ethanethiol, diethyl sulfide, or ethyl methyl sulfide. S-methyl thioacetate is most conspicuously a product of yeast metabolism, being produced from methanethiol. However, it is likely that the levels of dimethyl sulfide, sulfur dioxide, and perhaps methanethiol at the end of fermentation are a balance of substantial purging loss and replenishment by the action of yeast. There is an increase in the level of S-methyl thioacetate, at the expense of methanethiol, in ale that is naturally conditioned in the bottle. Prolonged postfermentation conditioning in tank also leads to an increase in the level of certain sulfur-containing volatiles, especially dimethyl sulfide and S-methyl thioacetate. Higher levels of sulfur volatiles were found in the same beer when packaged in kegs as opposed to bottles, presumably because of the extent to which volatiles are lost during purging operations.