Terroir and vine water relation effects on grape ripening and wine quality of Syrah/R99

A Syrah/R99 vineyard in the Stellenbosch area was used. The vineyard is vertically trained and spaced 2.75 x 1.5 m in north-south orientated rows on terroir with Glenrosa soil and west-facing slope. Irrigation (to 100% field water capacity) treatments were applied at different development stages [all stages (including berry set stage); pea size; véraison; post-véraison]. Combined effects of water status and ripeness level were investigated. Preliminary results are presented. Irrigated and non-irrigated vines differed in terms of soil water status, particularly during ripening. Vine water status during late ripening stages varied according to timing of water supply. Secondary leaves seemed most sensitive to water stress, but essential to buffer extreme terroir conditions. Vines displayed independence of soil water during late ripening. Irrigation favoured berry mass stability. Sucrose flow to berries was restricted at the last ripeness level, indicated by increased concentrations in bunch rachis. This may serve as tool to determine a window for harvesting. The window from ripe to over-ripe grapes was reduced when vines were exposed to lower soil water levels. Similar anthocyanin patterns found with skin and whole berry extraction and reduced skin sucrose contents indicated disintegration, oxidation and respiration during the last ripeness level in skins. Treatments being deficit-managed for a longer period showed earlier maximum wine quality (ripeness level 1). Vines irrigated at all development stages and those irrigated at pea size stage, showed later maximum wine quality (ripeness level 2). Wine quality of all treatments was reduced at the third ripeness level. Pre- and post-véraison cultivating conditions seem to have a determining effect on grape ripening. Preliminary results showed that the ripening period may be extended and berry condition maintained for longer by improved vine water status on a specific terroir.

Authors: Jacobus J. HUNTER (1) and Alain DELOIRE (2)

(1) ARC Infruitec-Nietvoorbij, Private Bag X5026, 7599 Stellenbosch, South Africa
(2) Agro Montpellier, UMR 1083 « Sciences pour l’œnologie et la viticulture », 2 place Viala, 34060 Montpellier cedex 1, France

Email: hunterk@arc.agric.za

Keywords: terroir, water relations, canopy, grape ripening, wine quality

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