An assessment of spruce wood as a replacement for peat in the production of whisky: chemical and sensory analysis of new make spirits

Abstract

Thermal decomposition of spruce wood and peat was investigated and compared using thermogravimetric analysis and pyrolysis-enabled gas chromatography mass spectrometry (GC–MS). Afterwards, new make spirit samples were produced using both materials as sources of smoke, with the resulting spirits analysed using a combination of NMR, FT-ICR-MS and sensory analysis. Thermal degradation studies revealed that while spruce wood and peat both feature similar compositional biopolymers, spruce contains relatively more (poly)carbohydrates and less lignin than peat. Additionally, while both materials showed dominance of guaiacyl (G) units in the lignin structure, the abundance of G units was more extreme in spruce wood. Desirable phenolic species were produced upon pyrolysis of both peat and spruce wood, however, greater abundance of them was produced by peat. These observations were reflected in our results of spirit analysis, which showed similar levels of some phenolics, in particular cresols, but greater amount of methoxyphenolic species in peated new make spirit. Sensory analysis revealed that spruce smoked new make spirit could be described as “lightly smoked” with no unpleasant off notes detected by the sensory panel, which aligns with our instrumental findings. For a better comparison of the balance of smoke aromas, the intensities of wood and peat smoked new make spirit would need to be matched. These results do suggest that some softwoods may be used to provide a smoky aroma with similarities to that traditionally associated with peat.