1.1. Sensory Profiling of Beer
Sensory properties of beers are of paramount importance for consumer acceptance. The extent to which the assessment of taste, flavors and aromas in beers has occupied the minds of brewers, flavor chemists and sensory scientists is evident from the ample literature compiled on the subjects [1
]. Beer flavor has been studied extensively in the domain of analytical chemistry (e.g., [2
]), and indeed it is well known that a large number of compounds affect the sensory properties of beer, such as sugars, organic acids, hop bitter acids, polyphenols, DMS and carbonyl compounds [3
]. Although instrumental measurements on chemical and physical parameters in beer are obviously valuable, there is hardly a one-to-one relationship between an analytically determined compound and a specific sensory attribute [1
], which is why human assessors must be employed to collect information on the sensory quality of beers.
Indeed, sensory scientific approaches to evaluation of beer flavors abound in the literature, with a significant share of this work even originated from within the brewing industry (e.g., [4
]). Previous studies have used sensory descriptive analysis (DA) for a variety of applications: e.g., to relate sensory characteristics of beer to its chemical composition (e.g., [2
]), ageing [5
] or storage conditions [6
]; to define different brewing styles from a sensory standpoint [7
], and to predict consumer preferences [8
The majority of these studies have employed highly trained panels for sensory profiling of beers. However, attempts at using consumers for sensory profiling of beers have also been reported. In a classical study comparing panels with different degrees of expertise in a DA task, Clapperton and Piggott [9
] found that trained subjects and consumers are able to produce similar profiles (though training was found to improve reproducibility and discrimination). Later, Gains and Thomson [10
] successfully conducted a home use test (HUT) in which they used a consumer population for sensory profiling of a selected sample of lager beers. They concluded that consumers can validly profile beers, provided that sensory differences are not extremely subtle, especially if they have at least some degree of familiarity with the product [10
]. A similar conclusion was reached by Chollet and colleagues [11
] who used a combination of sorting and a fast descriptive task.
1.2. Aims of the Present Study
Although DA is known to produce detailed, robust and repeatable results, as documented by numerous scientific publications (for a review on the topic, see [12
]), it has also certain drawbacks. It is a very slow method, particularly because of the extended training phase. Second, it is a very costly method. Maintaining a sensory panel is (usually) not affordable for, e.g., craft brewers, and can be a significant spending also for large brewing companies. Lastly, it is possible that the trained assessors experience the product differently from the final consumers, and/or that they may take into account sensory characteristics that may be irrelevant for the consumers [13
], providing high quality results but with low external validity.
In order to address these drawbacks, a number of alternative descriptive methodologies have been proposed over the years, most of which require little or no training, and are easily implementable with trained panelists or consumers alike.
In the context of this research, it was considered of interest to explore the suitability of new approaches for the sensory profiling of beers. It was chosen to focus primarily on Napping®
]. This choice was motivated by a number of factors: this method is reportedly fast, low-cost, and it requires a smaller number of assessors than other sensory profiling methods [15
]. Furthermore, it has been used successfully, with both trained and untrained assessors, for sensory profiling of several beverages categories, such as wine, beer, and high alcohol products [14
method was introduced by Pagès [14
], and is a specific variant of the original projective mapping [22
], a method that is based on the idea that inter-perceived product differences can be expressed as a Euclidean configuration in a unique session.
The method consists in presenting the samples simultaneously to each assessor, together with a large rectangular sheet of blank paper of a size similar to a standard A2 sheet (60 by 40 cm), which resembles a paper tablecloth (the word “napping” derives from ”nappe”—the French word for “tablecloth”). Assessors are then instructed to evaluate the perceived the similarities (or dissimilarities) between the samples, by positioning them on the sheet in such a way that two samples should be placed very close if they seem identical, and distant from one another if they seem different. It is stressed that assessors have to do so according to their own criteria, and that are not right or wrong solutions. At the end of the task, assessors usually write the sample code in the place it occupies on the sheet, or use post-its notes to that effect.
These data are digitalized using a coordinate system (the origin is customarily placed in the bottom left corner, though it can be placed anywhere) and entered into a data matrix with products as rows, and X- and Y-coordinates as columns. Finally, because Napping®
itself is purely a sorting task, it has become customary to instruct the assessors, once they have reached a final configuration, to add a list of sensory attributes that they find appropriate to describe the samples. This quick descriptive procedure is usually referred to as Ultra-Flash Profiling (UFP, [20
A visual representation of a completed Napping®
(+UFP) sheet is shown in Figure 1
methodology has been recently suggested as advantageous for rapid evaluations of beer as rapid product screening tool, to obtain feedbacks on product and process specifications, and/or for generating a sensory vocabulary [15
]. For larger breweries, Napping®
may be an advantageous exploratory tool in preparation for more thorough sensory assessment. For craft breweries, which do not usually have access to conventional sensory panels, Napping®
can be a useful tool to, say, document the sensory outcome of experimental brews in a more systematic manner [15
Before one can advocate its adoption with confidence, however, it is important to understand methodological aspects of Napping®
more in depth. Of relevance in this paper is the type of assessors that are suitable for this task. Initial exploratory work has suggested that product expertise might increase panelist performance when evaluating beer with a Napping®
In the present work, we delve deeper and more systematically into the question of whether product expertise is related to the ability to provide a sensory profile of beers by a Napping® task. In particular, the aim of the present work was to compare the performance of three different panels with varying degree of beer-related expertise, with respect to two evaluative criteria: (1) perceptual similarity, i.e., the degree of configurational agreement between the sensory spaces obtained at individual panel level; and (2) descriptive similarity, i.e., the degree to which the three panels would use similar attributes to verbalize their impressions of the beers.