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Aroma Profiles Of South African Wines


Dr J Marais

The ability to guarantee authenticity and detect fraud in foods and beverages is becoming increasingly important internationally. In the case of wine, the ability to detect possible addition of aroma constituents to wine can only be based on an extensive knowledge of what naturally occurs in wine. The Wine Industry (Winetech) regarded this matter of extreme importance, and therefore called for a research project on the aroma profiles of a number of cultivar wines. The project commenced in 2005 and will probably be completed in 2008.

At present, different research institutions (ARC Infruitec-Nietvoorbij, University of Stellenbosch and University of Cape Town) collaborate in conducting this project. The aim of the project is to compile comprehensive databases ("fingerprints") on aroma components in wines of the most important South African cultivars, originating from the various geographical regions. Unwooded, young wines of six cultivars (Cabernet Sauvignon, Merlot, Shiraz, Pinotage, Chardonnay and Sauvignon blanc) are sampled annually from the Young Wine Show, as well as from origins not represented at this show. The wines of each cultivar are selected according to their regional distribution, and are therefore representative of the South African wine industry. The samples are 100% cultivar wines. About 70 to 100 samples per cultivar per season are collected.

Wine contains hundreds of volatile constituents some of which have no impact on aroma, some which only contribute to the general wine-like background, while others directly impact on aroma. Wine aroma components represent a variety of chemical classes and are present in widely divergent concentration ranges. The most important aroma groups in wine are: esters, higher alcohols, lactones, monoterpenes, norisoprenoids, methoxypyrazines, mercaptans, volatile phenols and wood-derived components. Because most impact aroma components are extremely aroma effective (low threshold values), very small amounts can have a major effect on wine characteristics. Fraud detection is based on deviations from levels of naturally-occurring impact compounds, and variations in the general profile or ratios between components, or both.

In addition, the composition of relevant commercial flavour essences and plant extracts are examined to supply support data. The results of this research will assist authorities in future to detect fraud.

Naturally, it is impossible to analyse all the relevant components in a single standard analysis. Therefore different methods are used, namely:

  1. Liquid/liquid extraction of volatiles using diethyl ether (GC-FID). This method gives a general wine aroma profile for all six cultivars (Managed by the University of Stellenbosch. Project Leader: Prof. P van Rensburg).
  2. Headspace extraction of volatiles (Solid Phase Micro Extraction). This method gives a general aroma profile of the headspace of wine for all six cultivars (Managed by the ARC Infruitec-Nietvoorbij. Project Leader: Dr. O. Augustyn).
  3. Headspace extraction of methoxypyrazines (Solid Phase Micro Extraction). This method gives a specific methoxypyrazine profile for Sauvignon blanc, Cabernet Sauvignon and Merlot (Managed by the ARC Infruitec-Nietvoorbij. Project Leader: Dr. I. Burger).
  4. Liquid/liquid extraction of mercaptans. This method gives a specific mercaptan profile for Sauvignon blanc, Cabernet Sauvignon and Merlot (Managed by the University of Cape Town. Project Leader: Prof. S. Burton).
  5. Headspace stir bar extraction followed by thermal desorption (HSSE-TD-GC-MS). This method gives a general aroma profile of the headspace and/or liquid phase for all six cultivars (Managed by the University of Stellenbosch. Project Leader: Prof. A. Crouch).
Dr. Johann Marais is the coordinator of this project.




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