# Comparison of Three Approaches to Assess the Flavour Characteristics of Scotch Whisky Spirit
## 4 Discussion
\begin{table}
\begin{tabular}{c c} \hline
**Methodology Comparison** & **RV Coefficient** \\ \hline QDA versus Napping & 0.906 \\ QDA versus GC-MS & 0.895 \\ Napping versus GC-MS & 0.927 \\ \hline \end{tabular}
\end{table} 
Table 2: RV coefficient from the HMFA comparison of the QDA, Napping and GC-MS data. both evaluations, so any differences in the product maps were due to the technique used rather than the panellists. When using QDA, the evaluations were split over several sessions, while Napping was carried out in a single session. This reduces sample preparation time and the amount of spirit required. This can be particularly important in applications where there is a limited amount of sample available. The data analysis used in Napping, MFA, gives a product map but does not provide information on the degree of difference in the sample set [18]. The nature of the data means that they can only be used to compare samples assessed in the same session, while with QDA data can be compared across sessions. The nine spirits used in this study was a manageable number, but there is a limit to the number of samples that can be compared using Napping. Even when sensory tests are carried out under carefully controlled conditions by highly trained panellists, the data are subjective and unavoidably influenced by their sensitivities to individual flavour compounds. A panel of assessors is required to obtain meaningful results. Other researchers have observed that, with high alcohol strength spirits, only a limited number of spirits and attributes can be assessed during a session if you want to retain the quality of the data [55]. The alternative is to use an analytical method, which is more reproducible, less subjective and allows for the analysis of large sets of samples. GC-MS is an established method which is used to understand how the chemical composition of a product influences flavour, to predict flavour, and to show which flavour compounds are important to create specific characteristics [34; 52; 56]. In this study, the GC-MS semi-quantitative analysis of 96 chemical compounds gave a similar product map showing the same spirit groupings as the two sensory approaches. The spirits which had high ABVs and lighter flavour characteristic (_fruity, floral, solventy,_ and _sweet_) contained higher concentrations of esters, certain alcohols and arenes. The low ABV, which had heavier flavour characteristics (_fiently, cereal, sour, oily,_ and _sulphury_) contained lower levels of these compounds and increased concentrations of other alcohols and aldehydes. This agrees with previous research, which shows that aldehydes originate from malt and can be reduced to their unsaturated counter parts during fermentation. Hence the degree of fermentation, final ABV, is important for the reduction. In the spirits with a low ABV, the fermentation was incomplete, leaving the higher level of aldehydes [4]. Additionally, furfural concentrations emanate from the grain [3]. While GC-MS gave rich information about the chemical composition, the abundance of compounds and their ratios, the link between this and perceived flavour is more difficult to interpret due to masking effects and compound interactions. For example, the most abundant compounds present in the spirits were esters, which have fruity flavours, but the spirits were not perceived as predominantly fruity. Previous research on American bourbon whiskey has suggested that a chemical recreation with a selection of compounds is possible but is not an easy task [57]. A disadvantage of chemical compositional analysis is that there is typically not an individual compound contributing to a single flavour. For example, the nutty character of malt whisky has been positively linked to 2,5-dimethylpyrazine, 2-furanmethanol and ethyl benzoate, while \(\gamma\)-nonalactone has a negative correlation [58]. In another study, the green flavour of malt whisky was linked to aldehydes and nonan-2-ol.