# Comparison of Three Approaches to Assess the Flavour Characteristics of Scotch Whisky Spirit
## 1 Introduction
It is important that the whisky industry has a means of measuring flavour characteristics, so that these differences can be both described and quantified. In this study three different methods for assessing the flavour of new make (unmatured) Scotch whisky spirits were compared: two sensory methods (Quantitative Descriptive Analysis and Napping) and one instrumental method (Gas Chromatography-Mass Spectrometry). Sensory evaluation is the assessment of samples by a panel of human assessors using controlled methods and conditions. In this paper, the use of Quantitative Descriptive Analysis (QDA) is considered as one of the most common approaches for profiling the flavour characteristics of a product. This technique was developed in the 1970s [14; 15] and since then has been widely used in food and beverage applications. Panellists individually rate the intensities of a pre-selected set of flavour characteristics using a scaling system. In the case of whisky spirits, the vocabulary is already well established, being based on The Scotch Whisky Research Institute Flavour Wheel. This flavour wheel was firstly developed in the 1970s and is now widely used across the industry [3; 16; 17]. QDA is time consuming and requires a trained sensory panel. However, it has been shown to give informative and comprehensive results, highlighting subtle differences, and making it easy to compare samples [15; 17; 18]. In recent years, several rapid sensory methods have been developed and used for the evaluation of similar product categories, such as wine [19; 20] and beer [21; 22; 23]. One of these rapid methods is Napping, also called projective mapping. Napping was first introduced in 1994, being further developed in the 2000s [24; 25; 26]. It gets its name from the word \"nappe\" which is the French word for tablecloth, on which the technique was first performed. Panellists are asked to arrange samples in a two-dimensional space based on similarities and differences between them, placing samples that are different far apart and samples which are alike close to each other [18]. Once placed on the nappe, the panellists give a short description of each sample or group of samples. Untrained panellists can be used for this approach, as they use their own criteria to sort and describe the samples. Previous studies, with no or low alcohol products have shown that QDA and Napping give similar product maps [18; 27; 28; 29; 30; 31]. Gas Chromatography-Mass Spectrometry (GC-MS) is an analytical method that can be used to separate and identify compounds present in a complex mixture, such as whisky. In whisky spirit, many of these compounds are flavour active, so differences in their relative abundance contribute to flavour differences. GC-MS is used in the whisky industry for quality control purposes, product development and for product authentication [32; 33]. However, due to equipment costs and the need for trained personnel, it is not a standard method, generally only being used in larger laboratories. GC-MS is also used for research purposes, often in combination with sensory techniques [34; 35; 36]. The aim of this study was to evaluate the information that each of the three techniques (QDA, Napping and GC-MS) provides on flavour differences across a set of unmatured whisky spirits, including how the spirits were grouped using the three methods, and the strengths and weaknesses of each approach.