Peat source and its impact on the flavour of Scotch whisky

Abstract

Peat is used as a source of flavour compounds in Scotch malt whisky production when it is burned during malt kilning. The aim of this project was to establish whether peats from different locations in Scotland are chemically distinct and could consequently impart variations in flavour to malt whisky. Peat samples from four geographical locations (Islay, Orkney, St Fergus and Tomintoul) were distinguished by Fourier Transform Infrared (FT-IR) spectroscopy. Analysing peat samples using Curie point pyrolysis in combination with Gas Chromatography-Mass Spectrometry (Py-GC-MS) showed that peats from Islay and St Fergus were rich in lignin derivatives while those from Orkney and Tomintoul had higher levels of carbohydrate derivatives. Also, Islay and Orkney peats were rich in nitrogen-containing heterocycles and aromatic hydrocarbons respectively. A laboratory-scale peating process was developed and malt was prepared using peat from the four locations. This malt was mashed and fermented and the wash distilled on a laboratory-scale. Analysis by GC-MS showed that some peat- derived compounds such as lignin-derived syringols were not transferred to the spirit. Nevertheless, principal components analysis of the GC-MS data revealed that the spirits grouped into a similar pattern as that derived from the peat analyses. Assessment of the spirits by sensory panel revealed significant flavour differences; in particular spirits prepared with Islay peats were distinguished by burnt and smoky aromas. These findings indicate that if distillers change the source of their peat, either through choice or by necessity, they must take into account the possible influence that this could have on the flavour character of their product.