Identification of key aroma compounds in Shiraz grapes and wine
Background
Spicy ‘black pepper’ aroma is an important attribute of some high quality Australian Shiraz wines. Earlier work in this project at the AWRI resulted in fractions isolated from peppery Shiraz grapes, which contained a single component that gave a strong spicy/peppery aroma. This was determined from gas chromatography/mass spectrometry/olfactometry (GC/MS/O), which involves assessors smelling the components chemically separated from the mixture of compounds in a grape fraction.
It was clear from this work that the aroma associated with the peppery character in the grape fractions bore a striking resemblance to the aroma of commercial white pepper. Therefore, we analysed a crude extract of ground white pepper by GC/MS/O and found that, not only was the compound responsible for the peppery character in the grapes also apparently present in white pepper, but that it was also one of the most potent, if not the most potent odorant in the white pepper sample.
Progress
With the help of an authentic reference compound, we identified the compound rotundone, one of the class of compounds known as sesquiterpenes, as the potent peppery odorant in both the peppercorn and grape extracts.
Rotundone and its deuterated analogue were then prepared synthetically to provide adequate quantities to act as reference compound and internal standard, respectively.
Various grape homogenate and wine samples on which we had previously conducted sensory studies were analysed for rotundone. Grape homogenates with the highest ‘pepper’ score were shown to contain the highest concentration of rotundone. Furthermore, the wine made from the same vineyard as the most peppery grape samples had the highest rotundone concentrations. Similarly, the red wine survey and sensory data demonstrated the widespread presence of rotundone in red wine and established, as observed for grapes, a close relationship between the concentration of this pepper impact compound and the intensity of the ‘peppery’ aroma in red wine.
From sensory analysis the aroma detection thresholds of rotundone were determined to be 16 ng/L in red wine and 8 ng/L in water. Interestingly, some 20% of sensory panelists could not detect the aroma of rotundone, even at extremely high levels.
Studies are continuing to assess the rotundone levels in grapes and wines from various Shiraz clones, and the impact of viticultural treatments and effect of regionality.
Highlights
- Rotundone was identified as the compound responsible for the characteristic ‘pepper’ aroma of some Australian Shiraz wines
- Rotundone levels in grapes were strongly related to the amounts found in the corresponding wines
- Aroma detection thresholds were determined for rotundone in red wine and water
- Rotundone levels in grapes and wines are affected by vintage and regional differences
- Many common herbs and spices were found to contain rotundone, including black and white peppercorns, which had by far the highest concentrations
Project leader: Dr David Jeffery
Project team members:
Publications:
1065 Herderich, M.J.; Pretorius, I.S. Sniffing out Shiraz's secret. Aust. N.Z. Wine Ind. J. 23(4): 21-23; 2008 (click here to order).
Jeffery, D. Siebert, T. Capone, D. Pardon, K. Van Leeuwen, K. Solomon, M. Grape and wine pepper aroma – analytically challenging but we sniff it out in the end. Technical Review 180, 11–16; 2009 (click here to access Technical Review).
1030 Pollnitz, A.P.; Wood, C.; Siebert, T.E.; Parker, M.; Capone, D.L.; Elsey, G.M.; Eggers, M.; Meier, M.; Vössing, T.; Widder, S.; Krammer, G.; Sefton, M.A.; Herderich, M.J. Pepper aroma in Shiraz. Blair, R.J.; Williams, P.J.; Pretorius, I.S. (eds) Proceedings of the thirteenth Australian wine industry technical conference, 29 July–2 August 2007, Adelaide, SA: Australian Wine Industry Technical Conference Inc., Adelaide, SA., 157–159; 2008 (click here to order).
1061 Siebert, T.E.; Wood, C.; Elsey, G.M.; Pollnitz, A.P. Determination of rotundone, the pepper aroma impact compound, in grapes and wine. J. Agric. Food Chem. 56: 3745-3748; 2008 (click here to order).
1060 Wood, C.; Siebert, T.E.; Parker, M.; Capone, D.L.; Elsey, G.M.; Pollnitz, A.P.; Eggers, M.; Meier, M.; Vössing, T.;Widder, S.; Krammer, G.; Sefton, M.A.; Herderich, M.J. From wine to pepper: rotundone, an obscure sesquiterpene, is a potent spicy aroma compound. J. Agric. Food Chem. 56(10): 3738-3744; 2008 (click here to order).