Pietro PREVITALI1, Nick DOKOOZLIAN 1,2, Luis SANCHEZ2, Bruce PAN2, Kerry WILKINSON1, Christopher FORD1
1 The University of Adelaide and Australian Research Council Training Centre for Innovative Wine Production
2 E. & J. Gallo Winery
Email contact: pietro.previtali[@]adelaide.edu.au
AIM: The study of cultural practices to delay ripening and the characterization of their effect on wine composition is important in the mitigation of accelerated ripening caused by higher temperatures and frequent water stress events.1 The desynchronization between sugar accumulation and anthocyanins and organic acids during advanced ripening reported in previous studies frequently results in sub-optimal phenolic and aromatic maturity at the targeted sugar levels for winemaking.2,3 In this study, the effect of different rates of ripening on the chemistry of Cabernet Sauvignon wines was studied to explore if delayed ripening would result in higher quality wines.
METHODS: Fruit sugar accumulation rates were manipulated by means of crop load manipulation treatments and late season irrigation. Fruit was harvested at 26 °Brix and submitted to small-lot research winemaking. The basic chemistry and the composition of phenolic and aroma compounds were analyzed in the final wines.
RESULTS: The vineyard treatments returned three kinetics of sugar accumulation. A faster sugar accumulation (1 week earlier) was obtained by reducing crop load while a combination of crop removal and late season irrigation delayed ripening (2 weeks later) compared to untreated vines. Such effects of crop load and late season irrigation were already reported previously.4 In the final wines, there were little or no changes in the basic chemistry in response to the ripening rate. Crop load affected mainly the profile of wine aroma compounds, including both grape-derived and fermentation-derived compounds. On the other hand, an increase of irrigation late in the season led to an increase in phenolic compound levels, resulting in improved color and mouthfeel characteristics. Ripening was delayed by the interaction of cluster thinning and late season irrigation, which in turn led to higher concentrations of both volatile and phenolic compounds and further improvement of wine quality. In response to a slower sugar accumulation, an improvement of primary quality indicators of grape quality, such as lower green compounds and higher anthocyanins, translated into higher wine quality. Similar effects on these wine components were already observed in studies in which ripening was delayed by other means.5
CONCLUSION: This study provides further confirmation that delayed ripening is beneficial to improve wine quality in late-ripening varieties. Amelioration of accelerated ripening is especially critical in warm and dry viticulture regions with long seasons, while the treatments investigated may not be necessary nor result in the same outcomes in cool wine regions. It was also shown that crop load and late season irrigation have a specific effect on aroma and phenolic compounds respectively, which deserves to be further explored in future studies.
1. Webb, L., Whetton, P., Barlow, E. Modelled impact of future climate change on the phenology of winegrapes in Australia. Aust. J. Grape Wine Res. 2007, 13 (3), 165–175
2. Sadras, V., Moran, M. Elevated temperature decouples anthocyanins and sugars in berries of Shiraz and Cabernet Franc. Aust. J. Grape Wine Res. 2012, 18 (2), 115–122
3. Sweetman, C., Sadras, V., Hancock, R., Soole, K., Ford, C. Metabolic effects of elevated temperature on organic acid degradation in ripening Vitis vinifera fruit. J. Exp. Bot. 2014, 65 (20), 5975–5988
4. Mendez, M., Sanchez, L., Dokoozlian, N. Crop load and irrigation management during the latter stages of ripening: effects on vine water status, fruit dehydration and fruit composition of “Merlot” grapevines. Acta Hort. 2011, 889, 67-74
5. Böttcher, C., Harvey, K., Forde, C., Boss, P., Davies, C. Auxin treatment of pre-veraison grape (Vitis vinifera L.) berries both delays ripening and increases the synchronicity of sugar accumulation. Aust. J. Grape Wine Res. 2011, 17 (1), 1–8