Malt whisky is made from malted barley, yeast and water, and contains volatile and non-volatile flavor compounds derived from both the raw materials and the production processes including malting, mashing, fermentation, distillation and maturation. Evaluation of the character attributes of malt whisky has mainly relied on sensory analysis and the relationships between sensory and chemical analyses are not well elucidated. Sensory analysis can outline the character and origin of flavor compounds in each process. Phenolic compounds are produced during the kilning of malted barley. Yeast and naturally occurring lactic acid bacteria affect the character during the fermentation process. Distillation in copper pot stills influences the behavior of sulfur compounds including polysulfides. Lastly, the role of maturation in oak casks involves the extraction and absorption of various compounds. Sweet volatiles and gustatory non-volatiles are extracted, while unpleasant sulfur compounds are absorbed. This review summarizes current data on the mechanisms underlying the formation of flavor compounds in malt whisky.

The fatty and sweet flavours in malt whisky were studied by GC-olfactometry and GC-mass spectrometry. These compounds were identified as β-methyl-γ-octalactones, γ-nonalactone, γ-decalactone and γ-dodecalactone. Although β-methyl-γ-octalactones were present in matured malt whiskies and considerable amounts of γ-nonalactone were present in all, the content of γ-decalactone and that of γ-dodecalactone varied in both matured and non-matured malt whiskies. A high correlation was observed between the scores of descriptive analysis and the γ-decalactone and γ-dodecalactone content. The malt whiskies containing certain amounts of both γ-decalactone and γ-dodecalactone had sweet and fatty flavours, and thus it is evident that these lactones contribute to the quality. Both of these lactones are thought to be important for the flavour of malt whisky.