# Comparison of Three Approaches to Assess the Flavour Characteristics of Scotch Whisky Spirit
## 1 Introduction  
Scotch whisky is one of the most important products for Scotland's economy, with 133 operational distilleries adding a gross value of GBP 5.5 billion to the economy every year. This industry employs over 10,000 people in Scotland alone and attracts 2 million visitors to distilleries every year [1]. Scotch malt whiskies must be produced using malted barley, yeast and water, before being matured for at least three years in Scotland in oak casks [2]. This maintains the high standard of this spirit. Apart from caramel for colour standardisation, nothing can be added. So, the process steps and quality of the raw materials are essential to the final flavour. The production of Scotch malt whisky includes several steps: malting, mashing, fermentation, distillation, and maturation. The choice of raw materials and process parameters dictates the final flavour. Malting allows for the amylolysis of barley starch for the conversion to fermentable sugars. Flavours originating from this process are malty, bready, chocolate-like, or damp-straw notes. Furfural is a compound responsible for agrainy/marzipan aroma and 2-and 3-methylbutanal responsible for malty aroma [3]. Other aldehydes, such as hexanal and 2,4-decadienal, give grassy and bean-like aromas. These are created during malting but are reduced by kilning, the subsequent drying of the malt [4]. Mashing uses hot water to breakdown the starch further into fermentable sugars. There is relatively little published research on mashing and flavour, though off-flavours related to oxidation during mashing have been analysed [4; 5]. Yeast is added to the resulting word and the alcoholic fermentation converts the sugars to ethanol and carbon dioxide. The focus of this study are the secondary metabolites produced by yeast. Esters and higher alcohols are produced during fermentation resulting in fruits and floral notes. Aldehydes originating from the malt can be reduced to their saturated counterparts [4]. Peppery/pungent notes during fermentation can occur due to other active microorganism like _Lactobacillus_ spp. which can produce acrolein [3]. Distillation subsequently reduces sulphur and meaty notes due to interactions of sulphur compounds with copper in the still. These include dimethyl trisulphide, a compound responsible for rotten vegetable type flavours [6]. The cut point, the fraction of the spirit collected, also affects the composition and flavour. The distilled spirit is then filled into oak casks for at least 3 years to mature to become Scotch whisky. Desirable flavour compounds are extracted from oak, such as vanillin (vanilla aroma) and oak lactone (coconut). At the same time unpleasant flavours, such as dimethyl sulphide, are reduced [3; 7]. In authenticity analysis for Scotch malt whisky, the concentrations of methanol, 1-propanol, methylpropan-1-ol and 2-methyl and 3-methyl butanol are used as markers [8]. Further important flavour compounds are acetaldehyde, ethyl acetate, acetal, isobutanol, fatty acids and fatty acid ethyl esters [3; 9]. Most published research and data on Scotch whisky and its flavour composition are related to the maturation or the authenticity of the final product. However, new make spirit analysis and research are important to ensure a complementary pairing of the style and character of the spirit with the right cask. For mashing and fermentation, the focus to date has mainly been on high yields [7; 9; 10; 11]. Recently there has been increasing interest in other areas, such as use of heritage barley varieties [12] and new yeast strains to enhance flavour diversity before maturation. The spirits examined in this paper were produced using a range of yeast strains. The metabolism of different yeast strains can vary, which alters the ratios of the secondary metabolites, i.e., flavour compounds, that they produce [13]. These strains had been used with the aim of exploring the impact of yeast on flavour.