# Comparison of Three Approaches to Assess the Flavour Characteristics of Scotch Whisky Spirit
## 4 Discussion
However, even after extensive research the levels of these compounds only gave an indication and could not totally recreate the flavour [56]. This study showed that while there were a range of compounds contributing to certain flavour characteristics, other flavours did not appear to be linked to single compounds. A good example are _cereal_ notes, which were perceived at relatively high levels in several of the spirits. None of the compounds measured in our GC-MS analysis were described as having this flavour. Either the compounds responsible were not detected, the flavour descriptors on the Good Scents Company website were too vague or, as previous research suggests, this _cereal_ character is due to an interaction of several compounds. Around one eighth of the compounds identified in the spirits could not be classified as there was no flavour description available in the literature. This may be because the compound is not flavour active, in which case it can be ignored. However, there may have been compounds that were detected in this analysis that had not previously been included in sensory studies. In this case, their potential flavour impact may have been overlooked. Gas chromatography-olfactometry-mass spectrometry (GC-O-MS), which combines an instrumental with a sensory analysis, could be applied to identify which compounds are flavour-active. Sensory thresholds are also important. Some compounds have much lower thresholds, having more of an impact at lower levels than compounds with higher thresholds. However, since there are no data available on threshold levels for many of these compounds, and they were not quantified, it was not possible to account for this factor in the analysis. Previous research conducted to determine the flavour threshold of single compounds showed that it is still difficult to calculate the overall flavour perception in mixtures of several compounds [34; 52; 56; 57]. The final issue that causes problems when linking GC-MS data to flavour perception is that, although an appropriate method was selected for this analysis, SPME selectively extracts some compounds more efficiently than others. Less volatile compounds, in particular, are more difficult to detect using GC-MS. This makes it harder to identify all compounds that give heavier characteristics, such as phenols, fatty acids or arenes, which are likely to have been more prevalent in the lower ABV spirits. Nevertheless, the data can be semi-quantitatively compared. While a comparison on a quantitative level showed that strains with a high ABV had, in general, higher peak areas of compounds, the real flavour can only be determined through sensory evaluation. Data collected across the three analyses revealed two main differences among the spirits. The biggest difference in both composition and sensory character was related to the ABV of the spirit, the level of alcohol that had been produced by the various yeast strains during fermentation. Higher alcohols, such as 2-methyl-1-propanol or isoamyl alcohols, distil later because their volatility increases with reducing alcohol concentration [59]. Solely based on the distillation effect, the opposite of what would be expected was observed, with these compounds being found in higher levels in the high ABV spirits. These compounds are fermentation products and are more prevalent in complete fermentations, resulting in higher ABVs. Most of the late eluting compounds detected by the chosen GC-MS method were linked to flavour descriptors such as _sweet_, _only_, or _fruity_. This could indicate that heavier compounds linked to _sulphury_, _fentity_, _creal_, or _stale flavours_ were not detected by the chosen method, or that they were only produced in low levels which could be linked back to the yeast strains used. All three analyses also revealed more subtle differences between the spirits. Spirit B was differentiated from the other spirits by all three methods, with GC-MS differentiating it most.