The forms in which sulphur dioxide can occur in beer (dissolved, as sulphite and bisulphite ions, and reversibly bound to compounds such as aldehydes, ketones and sugars) are described together with its sources (yeast metabolism, the treatment of raw materials and processing aids, and the direct addition of sulphurous acid or sulphites). Sulphur dioxide has antioxidant and antimicrobial properties which make it an effective preservative, and when sulphur is burned in directly fired malt kilns it limits the formation of N-nitrosodimethylamine in the malt. In addition, it can combine with carbonyl compounds in a way which reduces the sensory impact of the carbonyls which cause stale off flavours. However, at high concentrations it can itself cause sulphury off flavours. Methods for the analysis of sulphur dioxide in beer and brewing materials (the Monier-Williams distillation technique and its variants, iodometric titration, spectrophotometry, flow injection techniques using spectrophotometry or sensors, selective electrodes, enzymic assay kits, and chromatographic methods including headspace gas chromatography, different forms of ion chromatography and HPLC) are reviewed, the legal restrictions on its use in various countries are summarized, its food safety status is described (it is not very toxic, but can trigger asthmatic attacks in some individuals who are sensitive to it), the mechanisms of its antioxidant, staleness masking and antimicrobial actions are explained and its fate in beer is discussed together with the possible alternatives to its use as a preservative.
Keywords : additive analysis beer off flavour properties raw material stabilisation sulphur dioxide survey