1. Introduction
In the last decade, the wine produced from indigenous Greek grape varieties has been increasingly appreciated in the global wine market [
1]. Assyrtiko, Malagousia, Moschofilero, and Roditis, as white varieties, and Agiorgitiko and Xinomavro, as red varieties, are gaining ground among other prestigious international grape varieties [
2]. Assyrtiko is the most well-known Greek grape variety and initiated the discussion about Greek wine throughout the wine world [
3]. Furthermore, it is the first Greek grape variety planted for commercial purposes in other countries, such as Australia, Cyprus, and Lebanon, while new plantings are growing in Italy, South Africa, and the USA. Assyrtiko is believed to have originated from the volcanic island of Santorini, but it has now been planted throughout Greece [
3,
4]. Assyrtiko wines have been described as having lime, passion fruit, beeswax, flint, and ‘salty’ aromas [
5]. Μalagousia is another relatively well-known white variety. This grape variety was saved from extinction: most growers have abandoned it because of its sensitivity to oidium, but its distinctive aroma contributed to its re-plantation. It is planted all over the country and not related to any Protected Designations of Origin (PDOs) [
4]. The aromatic profile of its wines ranges from herbal, minty, and citrusy to peachy and tropical, as well as floral [
3,
6]. Moschofilero is a variety located in northern Peloponnese, and it is the unique variety of the single varietal PDO Mantinia. The aromatic profile of its wines ranges from honeydew, red apple skin, and cantaloupe to grapefruit zest, lemon, and lime [
7]. It has also been described as having floral aromas, specifically that of rose petals [
6]. Roditis is one of the most planted varieties in Greece, and its aroma has been characterized as citrusy [
8], melon [
6], and sometimes mineral [
6,
8].
Wine aroma is modulated by different viticultural parameters, such as the climate and soil of the vineyard; the variety and clone; viticultural practices; winemaking procedures, such as pre-fermentation processing, yeast strain, and alcoholic fermentation conditions; and wine treatments from fining to bottling [
9]. However, despite all of these parameters, most wines exhibit a characteristic and distinctive odor according to the grape variety from which they are produced [
9]. All of the previously mentioned parameters can enhance or reduce this character.
The aroma profiles of the wines of the aforementioned main Greek commercial grape varieties are described in popular sources, such as books [
4,
6] and internet blogs [
3,
7,
8]. However, scientific research on the typical characteristics of these varieties is scarce or even lacking. In particular, the wines produced from the aforementioned white grape varieties lack scientific resources that depict their characteristic aromas. In contrast, the literature has focused mainly on the red grape variety Agiorgitiko [
10,
11,
12,
13,
14]. Nonetheless, there is relatively abundant research on Greek wines in terms of physicochemical analyses that highlight significant characteristics of these wines [
15,
16,
17,
18,
19].
Conventional descriptive analysis has been used widely in the sensory analysis of wines [
20]. However, previous research has pointed out some disadvantages of applying this method to characterize wines. Wines have a very complex aromatic matrix, and it has been proven that people can only recognize a limited number of attributes in a complex matrix [
21,
22]. Furthermore, Lawless [
23] reported that rating intensity is a very difficult task when applied to complex products, such as wines. Thus, in this study, we chose to apply the frequency of attribute citation method. In this method, trained panelists are asked to review a list of attributes and check those that characterize each sample. This method has been applied in the past [
24,
25] and more recently [
26], and it has produced comparable results to those of other descriptive methods, such as sorting tasks, conventional descriptive analysis, and the pivot profile method [
24,
25,
26]. Furthermore, as this method does not require a rating task, cognitive fatigue is reduced; thus, it can be easily applied to wines.
Our research is the first scientific attempt to investigate the aroma profiles of wines of the varieties Assyrtiko, Malagousia, Moschofilero, and Roditis. We focused on the odor characteristics of these varieties and conducted a rigorous scientific study with a trained panel. The aim of this study was to elucidate how these varieties are characterized and differentiated from each other in terms of odor attributes by means of descriptive sensory analysis. We hypothesized that wines of the same variety would share a common sensory space in terms of odor character and that this profile would be distinct for each variety. Finally, we aimed to propose a guide to evaluate the performance of a whole panel and individual panelists in the case of wine typicality evaluation.
4. Discussion
In this study, data analysis showed that the panelists had an adequate performance as a whole, after excluding two of them, and individually. The overall performance of the panel was based on the reproducibility of their evaluations and their discrimination ability. The former was evaluated through multidimensional scaling (
Figure 1), Cochran’s Q test (
Table 4), and Friedman’s test (
Table 5), while the latter was assessed through the wine effect on attribute selection by Cochran’s Q test (
Table 4). Cochran’s Q test is widely used to analyze binomial data obtained by sensory panels [
39,
40]. To evaluate individual performance, we proposed the use of three different indices in order to draw more objective conclusions. Thus, we used index R, first used by Campo et al. [
25], index p
11, and the average chi-square statistic for the 17 wines. These analyses showed satisfactory results as well, allowing us to continue with further analysis of our data.
With regard to the sensory space of products and attributes,
Figure 2 reveals a clear character of Banana and Vanilla aromas for the samples of the Roditis variety, as well as Jasmine, Rose, and Honey aromas for the MSF9 and MSF10 samples of the Moschofilero variety. MSF3 and MSF8 are described with a more citrus-fruit-like profile (Lemon, Grapefruit), while the rest of the Moschofilero samples are mainly characterized by Citrus blossoms. The samples of the Assyrtiko variety are associated with aromas such as Honey (ASR4) and Lemon (ASR4, ASR1), as well as Earthy, Mushroom, and Nuts (ASR3). In MLG1–MLG4 samples of the Malagousia variety, Citrus blossoms, Rose, and Lemon are among the top two most cited attributes by the panelists (
Table 6). This can also be seen in
Figure 2, where, additionally, the odor of Mushroom seems to play a role for MLG2. Interestingly, some samples of different grape varieties, such as ASR4 and MLG1 or ASR1 and MSF3, seem to be more similar to each other rather than to other samples of the variety to which they belong. This is also supported by the results of cluster analysis (
Table 7,
Figure 3).
Indeed, some clusters are formed by samples of different grape varieties. Specifically, Cluster 1 consists of samples from two varieties, and Cluster 2 comprises samples from three varieties, whereas Clusters 3 and 4 are homogeneous in terms of varietal character. Taking into consideration
Figure 3 and
Table 7, the odor attributes describing Cluster 1 are Citrus blossoms, Banana, Grapefruit, and Lemon. Cluster 2 is characterized by Grapefruit, Lemon, Nutty, Earthy, and Mushroom odors. Floral aromas such as Jasmine and Rose, as well as Honey, are attributed to Cluster 3. Finally, Banana, Vanilla, and Rose seem to be important attributes for Cluster 4. It should be noted that Citrus blossom seems to be a common characteristic for all clusters—this can also be seen in
Table 6, where Citrus blossom is amongst the top three most cited terms for all samples—although, for Cluster 1, it is more important (see
Table 7). These characteristics are also evident in the spider diagram (see
Figure 4), where Citrus blossom is apparently cited frequently in all of the clusters, but it does not play an important role in the formation of all clusters, especially in Clusters 2 and 4 (see
Table 7). Furthermore, although the attributes Earthy, Mushroom, and Nuts are not stressed in the spider diagram, they seem to be important for Cluster 2 in the cluster analysis.
Regarding cluster formation and varietal origin of the studied wines, Ballester et al. [
41], similar to our work, reported that just belonging to a specific category is not enough for an item of this category to be described by the typical characteristics of the category. Furthermore, Rosch and Mervis [
42] stated that a typical product can be described not only by the attributes of its own category but also by some attributes of other categories. Within a category, items do have common attributes, but each item does not possess all of the key attributes of that category. Thus, membership in a category has been described as a continuum, where some items may exhibit more typical characteristics than others. Hence, it should not be regarded as an indicator of the absolute inclusion in a category or exclusion from that category [
43]. The importance of including samples from different varieties has also been stressed before in order to better explore the limits of the sensory space of a specific variety [
41].
Previous research on volatile compounds has revealed the presence of 2-phenylethyl ethanol and phenylethyl acetate in Moschofilero wines [
18,
44]. These compounds have been further associated with flower aromas, especially rose [
45]. This is in congruence with our finding that Moschofilero wines exhibit a floral aroma, including a rose aroma. Moreover, Kechagia et al. [
19] found key odorants that are responsible for fruity, honey, and floral aromas in Assyrtiko wines. Accordingly, in our study, Lemon, Grapefruit, and Honey were some of the most cited attributes for Assyrtiko samples. Tyrosol has been previously identified as one of the main phenolic compounds in seven Malagousia wines [
46], and it is also known to be responsible for the honey aroma [
47]. In our work, we observed that the honey aroma was frequently cited for one Malagousia wine (MLG1), as well as in wines of Assyrtiko (ASR4) and Moschofilero varieties (MSF9, MSF10). Moreover, tropical fruit and banana notes in wines of the Roditis variety have been previously reported [
48], but no scientific sources are available on the aroma character of this variety. These correlations from the literature stress the importance of investigating key odor compounds in the study of the characteristic aromas of wines of these grape varieties.
The present study is, to our knowledge, the first scientific attempt to systematically investigate the sensory aroma profiles of wines of the indigenous Greek grape varieties Assyrtiko, Roditis, Malagousia, and Moschofilero, followed by the assessment of panel performance. Other studies have researched the chemical profiles of some of these varieties and their association with other factors, such as prefermentative treatments [
19] and yeast interactions [
18]. However, there are no published reports in the literature that aim to identify typical aromas of these varieties. We implemented extensive panel training and a sensory technique, i.e., the frequency of attribute citation, which has been used over the last decade as a reliable and more intuitive alternative to other sensory descriptive methods [
24,
26,
49]. Furthermore, we used three indices to check panel reproducibility, followed by robust statistical analysis, in order to ensure objectivity in our conclusions. Reproducibility indices for binomial data have also been used in prior studies [
25,
50,
51], and they are of indisputable value, as all our data rely on panel assessments. Moreover, we used a common descriptor list for all wines, and no information was given during the evaluation of the variety of each wine so that we could obtain results with no such cognitive bias. However, we should mention that although all samples were of the same vintage, except for one, we could not account for possible different winemaking processes, as these samples were commercial wines from different winemakers and different areas. Another limitation of this study is that the number of samples for the Assyrtiko and Roditis varieties was relatively low to allow firm conclusions regarding their aroma profiles.
5. Conclusions
Overall, this study provides a guide to evaluate the performance of a whole panel and individual panelists through statistical indices and analysis. Furthermore, sensory data indicate patterns in the aroma profiles of the wines of four indigenous Greek white grape varieties. Specifically, wine samples of the Roditis variety exhibit mainly a Banana and Vanilla odor profile. Assyrtiko wine samples are characterized by Earthy, Mushroom, and Nutty odors, as well as Lemon and Honey for some of the samples. Malagousia wines are described as having Lemon, Grapefruit, and Citrus blossom characters, and they also share some descriptors with Assyrtiko wines, such as Mushroom and Earthy, and some with Moschofilero samples, i.e., floral and citrus notes. All Moschofilero wine samples exhibit a floral odor profile: specifically, Rose, Jasmine, or more Citrus blossom-like. Moreover, some samples of Moschofilero also reveal a Grapefruit, Lemon, and/or Earthy character, while others express Honey notes. Thus, as is already known, the present work shows that although some descriptors are more characteristic of each of the studied varieties, some samples of different varieties have overlapping profiles, and in some cases, samples of the same variety are quite different from each other.
Future work should focus on using samples that have been vinified with the same protocol. This way, the confounding factor of different winemaking processes will be excluded, and firmer conclusions about aromas that characterize each variety can be drawn. Nonetheless, we should focus not only on finding the key attributes of each variety but also on attributes to define the boundaries of the sensory space of each variety. These findings should ultimately be related and explained by chemical analysis in order to find key odorants that are responsible for those aromas.