# Comparison of Three Approaches to Assess the Flavour Characteristics of Scotch Whisky Spirit
## 3 Results
### Gas-Chromatography-Mass Spectrometry  
GC-MS identified a total of 96 compounds in the spirits. A full list of the detected compounds, their typical aroma descriptors, chemical group, and the peak area in each of the spirits can be found in Table 1 (Appendix A). PCA of the peak area data is shown in Figures 4 and 5. The first two dimensions accounted for 71.6% of the variance in the data.  
Figure 4: PCA scores plot from the analysis of the peak areas of 96 compounds present in nine new make whisky spirits (percentages next to the sample codes indicate the ABV).  
The separation of the spirits across Dimension 1, shown in the scores plot in Figure 4, was broadly related to ABV. High ABV spirits were located on the positive end of this dimension and low ABV spirits on the negative end. However, this tendency was not fully followed by the intermediate ABV spirits; spirits D and F were located close to the low ABV spirits, while E was located more towards the positive end, only being separated from the high ABV group by Dimension 2.  
The associated loadings plot (Figure 5) showed that the spirits were separated by chemical groups. Most of the compounds on the positive end of Dimension 1 were esters, certain alcohols and arenes, while those on the negative end were mainly other alcohols and aldehydes. Looking in more detail at the different compounds, the low ABV spirits contained higher levels of compounds that eluted early in the GC-MS run and alcohols.  
A further separation was observed across Dimension 2. Spirits E and B, which were both on the positive end of Dimension 1, were separated across Dimension 2. Spirit B was relatively high in propyl acetate, isobutyl acetate and pentyl acetate, while spirit E was rich in a variety of decanoate esters, such as isobutyl decanoate and isoamyl decanoate.  
In addition to the product map produced from the PCA, further information can be extracted from the GC-MS data by looking in more detail at the flavour characteristics typically associated with the identified compounds (Table A2, Appendix A). Over half of the compounds were typically described as having _fruity_ characteristics, while the next most prevalent flavour descriptions were _oily_, _sweet_, and _green_. Compounds with _soavy_, _finity_, _sour_ and _sulphury_ flavours were least common. Roughly one-eighth of the compounds could _not_ be _described_. This meant that there was either no flavour description,  
Figure 5: PCA loading plot from the analysis of the peak areas of 96 compounds present in nine new make whisky spirits. Loadings are shown in the form of chemical grouping of the compounds (numbering of the compounds is detailed in Table A2 (Appendix A)).  
indicating that the flavour of this compounds had not previously been researched, or that it was simply not flavour active. Some of the key flavour attributes used in the QDA and mentioned by panellists during Napping, namely _creal, meaty,_ and _smoky_, were not directly linked to any of the compounds measured using GC-MS. This indicates that either the compounds responsible for these flavours are not being detected by the instrument, or that these flavours arise from a more complex interaction of compounds. Correlating sensory with the analytical data using statistical methods, such as Partial Least Squares, can help to understand these interactions.