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Sensory panels often avoid the evaluation of mouthfeel sensations in wine, since it implies (for many non-wine experts) complex, and abstract concepts. However, mouthfeel is an important dimension of wine quality, and it is, therefore, necessary that these properties are also included in routinely sensory tests. In our recently completed Winetech funded research project IWBT W13/02, “Rapid descriptive sensory methods for wine evaluation – special focus on further optimisation of rapid methods and streamlining of workflow”, we have developed two useful protocols for the assessment of mouthfeel in wine that can be used by sensory panels in the industry and research. This article describes the protocol that is based on the classic descriptive analysis (DA) method. In line with the objectives of project IWBT W13/02, we also optimised a rapid sensory method, polarised sensory positioning (PSP) to evaluate mouthfeel in wine. The rapid method does not require a trained DA panel and can be completed in shorter sessions. The protocol for the rapid method is discussed in a subsequent article.

 

What is meant by mouthfeel?

Mouthfeel refers to the sensory perceptions experienced in the mouth when a wine is consumed. Wine judges often describe wine as “full and round with good concentration, and length”, thereby implying that the product has good mouthfeel properties. While these phrases are commonly used in the popular media, people differ in their understanding of what exactly is meant by them. In scientific publications, several terms are grouped under so-called in-mouth sensations; these include fullness, heat, complexity, balance, length and mouthfeel.

 

Evaluation of mouthfeel by sensory panels

It is a challenging task to train a sensory panel to evaluate wine mouthfeel sensations. DA is one of our most accurate sensory test methods and provides two important outputs. Firstly, all the sensory properties that are perceived in a set of wines are identified and named by a panel of trained tasters. Secondly, panellists also score the intensity of each property on a line scale (ranging from 0 to 100, for example).

Physical standards are used to train a panel for the first task (identification of sensory properties). For example, a fresh lemon can serve as a standard for the lemon character in wine aroma. It is clear that all the panellists must have agreement on the sensations of the lemon character, as well as the particular word that describes the specific character, before the panel can proceed to assess the wines. With abstract concepts, such as length, complexity, and balance, there are no so-called physical standards, and an alternative plan must be made during training of the panel.

Another major challenge is to calibrate panellists to rate the intensities of the mouthfeel sensations on a line scale. It speaks for itself that the line scale must be used consistently by different panellists and on independent sets of wines; otherwise, comparative studies are not possible.

To illustrate these challenges: in this Winetech project, we wanted to evaluate the mouthfeel sensations of old-vine Chenin blanc wines (produced from vines 40 years and older) with the DA method. It is well known among wine experts that the old-vine Chenins have much more complex mouthfeel properties, compared to some younger vine Chenins. For panellists to use the line scale consistently to showcase these differences, they need to have in-depth experience and knowledge of the entire product category. This is seldom the case. Also in dealing with this challenge, adjustments had to be made to the standard DA protocol.

 

Framework for the assessment of wine mouthfeel sensations with the DA method

We gave an overview of the DA method for wine sensory evaluation in a previous WineLand edition (February 2016), with step-by-step graphic illustrations. Here we discuss the adjustments that we made to the DA workflow to deal with the two mentioned challenges.

 

Phase 1: Identification of mouthfeel sensations

The first phase of the DA method requires that the panel reach consensus on the sensory properties that can be perceived in a set of test wines. We adapted this phase for the mouthfeel sensations as follows: industry experts and the researchers firstly selected a set of old-vine Chenin wines that presented the sensory properties of the category well. A few Chenin wines with less complex mouthfeel were also included in the test set, to ensure variation in the intensity of the properties of interest. During a pre-tasting of the set by experts and researchers, a list of terms was compiled that described the wines’ mouthfeel properties. This set of wines was then used to train the panellists in the identification and naming of mouthfeel properties. This strategy is referred to as ballot training in the literature. In this way, the workflow developed in our research ensured that there was no need for the panel members to be experts in old-vine Chenins before they could serve on the panel.

 

Phase 2: Panel training

Standards, definitions, and calibration of panellists in the use of line scales

Physical standards were used, where possible, to familiarise the panellists with wine mouthfeel sensations. For example, for recognition of the property of ‘body’, an aqueous solution of carboxymethylcellulose at different strengths was used: 0.5 g/ℓ (low), 1.0 g/ℓ (medium/low), 1.5 g/ℓ (medium/high) and 2 g/ℓ (high). The inputs of the panellists were obtained and consensus reached to determine where the different strengths should be marked on the line scales.

For the mouthfeel properties complexity, length, and fullness, physical standards were not available and definitions of the concepts were used instead. The latter were obtained from the websites www.vinology.com, www.winespectator.com, and from published articles. During the training phase, the panellists discussed what they understood from each definition. The panel leader made sure that each panellist understood the concepts and that the panel reached consensus on these aspects before testing of the wines commenced.

Training was also given to panellists to reach consensus on the use of the line scales, to reduce day-to-day variation in their evaluations. Here we also deviated from the classic DA protocol. A reference wine, of which the intensities for the respective sensory attributes were pre-determined by the researchers and already marked on the line scales, was also provided to each panellist during the testing stage. Panellists were free to taste the reference wine during the testing to anchor their responses. This variation in the protocol improved the accuracy and repeatability of the panellists.

 

Conclusion

The workflow developed in our research for the evaluation of mouthfeel in wine with the DA method proved to be successful. Our trained panel could accurately profile the different intensities of mouthfeel sensations in a set of old-vine Chenins. The workflow can also be easily adapted to other wine styles.

Given the importance of mouthfeel in the evaluation of wine quality, the outcomes of the research made a significant contribution to increasing the portfolio of sensory testing methods for industry and research alike.

 

Acknowledgements

This research was made possible by Winetech funding, project IWBT W13/02: “Rapid descriptive sensory methods for wine evaluation – special focus on further optimisation of rapid methods and streamlining of workflow”. Winetech, the Institutes of Wine Biotechnology (IWBT) and Grape and Wine Sciences (IGWS), Stellenbosch University, NRF and THRIP are acknowledged and thanked for financial support.

 

References

Gawel, R., Oberholster, A. & Francis, I.L., 2000. A “mouthfeel wheel”: terminology for communicating the mouthfeel characteristics of red wine. Australian Journal of grape and wine research 6, 203 – 207.

Heymann, H., King, E.S. & Hopfer, H., 2014. Classical descriptive analysis. In: Novel techniques in sensory characterisation and consumer profiling (edited by P. Varela & G. Ares), pp. 9 – 41. Boca Raton: CRC Press, Taylor & Francis Group.

 

– For more information, contact Renée Crous at reneecrous@gmail.com, Valeria Panzeri at panzeri@sun.ac.za or Hélène Nieuwoudt at hhn@sun.ac.za. We can also be contacted at winwynsen@sun.ac.za.

 

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