Grape phenolics and their contribution to wine composition and sensory properties
Background
This project aims to improve our understanding of the relationships between viticultural practices, grape phenolic composition, wine composition and sensory properties.
Progress
We have continued to investigate pruning and irrigation effects on berry size and composition for Cabernet Sauvignon. Clear treatment effects were found with machine-pruned berries resulting in the lowest weights and the highest concentrations of anthocyanins, total phenolics and tannin in all vintages. Wines also showed compositional differences between treatments, but the trends were not as clear as those for berry composition. Higher anthocyanins, tannins and phenolics concentrations in berries did not always result in higher concentrations of wine anthocyanins, tannins or phenolics. The overall quality rating by winemakers was significantly lower for wines made with berries from machine-pruned vines than for wines made with berries from cane- and for spur-pruned vines in all vintages.
In addition, recent experimental work focusing on the relative contributions of seed and skin tannin to wine tannin has been successfully completed. This work was conducted using seven parcels of Cabernet Sauvignon grapes from five regions with a wide range of berry tannin concentration. Over 9,000 berries were de-seeded or de-skinned in order to investigate the composition of the berries and the wines resulting from micro-fermentations (100 berry ferments). These data indicate that berries of different phenolic maturity can give highly variable skin tannin:seed tannin ratios in finished wines.
Method development and optimisation for measurement of white grape and wine phenolics has continued. Work continues in the identification of the compositional basis for style and quality parameters associated with phenolics in white grapes and wines, and the positive and negative roles these compounds might play in defining taste and colour. This work has a strong collaborative focus through interaction with research groups at AWRI, The University of Adelaide and sector partners. A number of analytical techniques for phenolic profiling of white juice and wines are being developed and optimised.
Highlights
- The smallest berries do not always produce the highest quality wines.
- Berries of different phenolic maturity can give highly variable skin tannin: seed tannin ratios in finished wines, with skin tannin dominating sometimes and seed tannin other times.
- A number of analytical techniques for phenolic profiling of white juice and wines are being developed and optimised.
Project leader: Dr Paul Smith
Project team members:
Publications:
969 Parker, M.; Mercurio, M.; Jeffery, D.; Herderich, M.; Holt, H.; Smith, P. An overview of the phenolic chemistry of white juice and wine production. Aust. N.Z. Grapegrower Winemaker 509a: 74–80; 2007 (click here to order).
970 Parker, M.; Smith, P.A.; Birse, M.; Francis, I.L.; Kwiatkowski, M.J.; Lattey, K.A.; Liebich, B.; Herderich, M.J. The effect of pre- and post-ferment additions of grape derived tannin on Shiraz wine sensory properties and phenolic composition. Aust. J. Grape Wine Res. 13(1): 30–37; 2007 (click here to order).