Is there a link between coffee aroma perception and the level of FMT in Pinotage wines?

by | May 1, 2021 | Oenology research, Winetech Technical

Over the years, Pinotage has found its way into the South African and international market. Whether you like this style or not, coffee Pinotage is a well-represented style on the South African wine market. By just looking at the labels or the tasting sheets, many of these wines are described with coffee, mocha, or even chocolate notes, so consumers can easily pick the wines if they prefer this particular style. But is it really true?

The coffee aroma in wines has already been associated to specific molecules, such as 2-furanmethanethiol (FMT) in Bordeaux wines,1 and it is generally linked to the wine ageing in oak barrels and the wood piece size and level of toasting.2,3 Is there a link between this molecule and the coffee aroma in Pinotage wines? Or is it part of a marketing strategy?

To test this, we selected several Pinotage wines based on the same information available to any consumer: labels and tasting sheets. The sample set consisted of 15 wines, including two blind duplicates. Most of the wines were described by the producers with coffee/mocha/chocolate attributes, except for a few, which were purposefully chosen without these notes as control. The selected wines were evaluated by a panel of trained judges using a rapid method; the samples were rated on a scale from 0 to 100 for the one attribute we were interested in: coffee aroma. At the same time, we measured the levels of FMT in the same wines.4 The results from the chemical analysis and the rating exercise were put together to determine whether the concentrations of FMT and the intensity of the coffee aroma perception were correlated. Lastly, perceived intensity of coffee aroma was correlated with the number of coffee or coffee-related attributes found on the front and back labels of the selected wines.

Chemistry results

As can be seen from Table 1, the level of FMT covers a wide range, from 6 to 138 ng/L. There are three wines which stand out through their very high level of this compound 133 to 138 ng/L (PT4, PT6 and PT9), while most of the wines are in the 20 to 40 ng/L range. Looking at the other thiols, the wines are not very different from each other. All thiols are present above their odour thresholds. (More information about thiol profiles of various cultivars were presented in the article “Thiol profiles of single cultivar red wines” published in the December 2018 edition of WineLand.)

Rating exercise and correlation with the chemistry results

The rating task was considered of medium difficulty by the judges. Given that they had to rate only one attribute, the repeatability for the two blind replicates was excellent (PT1/PT1-R and PT2/PT2-R, Figure 1). Some of the wines marketed as “coffee Pinotage” (underlined in Figure 1) were evaluated quite low on the intensity scale for this attribute (<40 out of 100). Meanwhile, the three wines outstanding in their FMT content were also scored with the highest values in the sensory rating.

There was indeed a correlation of 81% between the FMT level and the perception of coffee aroma, indicative of a good correlation between the thiol concentration and the sensory perception. Possibly this is due to the particular aroma this thiol imparts to the wine, or to the Pinotage matrix, or a combination of both.

Sensory information was also matched with the information displayed on the front or a back label. Most of the wines marketed as “coffee Pinotage” showed a good correlation between the intensity of coffee aroma and the number of coffee and coffee-related descriptors. However, this was not always the case. Certain wines, despite using several coffee references on the bottle, were perceived with a low intensity.

FIGURE 1. Correlation between FMT concentrations (ng/L) and rating of coffee aroma. Underlined codes are for wines described as coffee/mocha/chocolate Pinotage on the bottle labels and tasting sheets. “-R” indicates a blind repeat.

Abstract

Producers have used the flavour potential of this “original” South African grape for different wine styles, one of them being the so-called “coffee style Pinotage”.

The study has shown a clear relationship between the levels of FMT and the perception of coffee aroma in South African coffee style Pinotage wines. However, not all the wines marketed as such were either perceived with a coffee aroma or chemically characterised by higher levels of FMT. The study showed that some of the wines marketed as coffee style Pinotage would be perceived as so; however, in some cases, it could be more a marketing strategy.

References

  1. Tominaga, T., Blanchard, L., Darriet, P. & Dubourdieu, D., 2000. A powerful aromatic volatile thiol, 2-furanmethanethiol, exhibiting roast coffee aroma in wines made from several Vitis vinifera grape varieties. Journal of Agricultural and Food Chemistry 48(5): 1799 – 802.
  2. Fourie, B.A., 2005. The influence of different barrels and oak derived products on the colour evolution and quality of red wines. MSc Thesis, Stellenbosch University, Private Bag X1, 7602 Matieland, Stellenbosch, South Africa.
  3. Fernández de Simón, B., Cadahía, E., Del Álamo, M. & Nevares, I., 2010. Effect of size, seasoning and toasting in the volatile compounds in toasted oak wood and in a red wine treated with them. Analytica Chimica Acta 660(1 – 2): 211 – 20.
  4. Mafata, M., Stander, M., Thomachot, B. & Buica, A., 2018. Measuring thiols in single cultivar South African red wines using 4,4-dithiodipyridine (DTDP) derivatization and ultraperformance convergence chromatography-tandem mass spectrometry. Foods (Internet) 7(9): 138. Available from: http://www.mdpi.com/2304-8158/7/9/138.

– For more information, contact Astrid Buica at abuica@sun.ac.za.

 

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