The role of water composition on malt spirit quality

Abstract

A series of distillery process waters was characterised by pyrolysis-GC/MS for humic substances derived from soils and vegetation in water in conjunction with dissolved organic carbon analysis. Additional analyses were carried out for phenolic compounds by HPLC, anions and cations by ion chromatography, and metals and colour by spectrophotometry. Over 70 organic compounds were identified, with waters from north and western areas of Scotland containing higher levels of peat-derived compounds, with organic carbon determined by the length of watercourse traversed. Ionic concentration of waters was related to the geology of the surrounding areas. Little variation was found in other measurements of water chemistry. Using these samples for mashing, spirits were produced with notable differences in character, particularly in terms of spirit ‘heaviness’. Chemical analysis of these spirits by GC/MS highlighted significant differences in levels of volatile higher alcohol and sulphur-containing compounds, although these did not correlate with sensory character. The influence of organic and inorganic constituents of water in isolation was considered by preparing a series of artificially-spiked waters produced for use in mashing, representing the range of variation present in industrial process waters. The presence of peat-derived compounds in mashing water caused increased ester and reduced higher alcohol production by yeast, whereas the presence of metal ions inhibited yeast activity. The resulting new-make spirits from ionic-supplemented waters showed minimal differences in sensory character, whereas those containing peat-derived compounds exhibited greater variation, with heavier, more complex spirit character.