Effect of mechanical leaf removal and its timing on flavan-3-ol composition and concentrations in Vitis vinifera L. cv. Pinot Noir wine

Background and Aims: Mechanical leaf removal of Pinot Noir vines was carried out in a commercial vineyard in Waipara, New Zealand in the 2007-2008 and 2008-2009 growing seasons. The aim was to investigate the effects of different timings on flavan-3-ol composition and concentrations in Pinot Noir wine produced from the treatments. Methods and Results: Treatments were leaf removal from the fruiting zone 7 days after flowering, 30 days after flowering and at veraison (by visual assessment), and no leaf removal (control). Proanthocyanidin concentrations in berries by the methylcellulose precipitation assay at harvest showed no difference between treatments, although the LR7 wine had the highest methylcellulose precipitable tannin concentration in 2007-2008, the LR30 wine had the highest concentration in 2008-2009 and the NLR wine had the lowest in both years; the 2009 wines had increased concentrations compared to 2008. Greatest concentrations of flavan-3-ol monomers by reverse phase high performance liquid chromatography were found in LR7 wines. An increase in the ratio of 2,3-trans to 2,3-cis flavan-3-ols was observed with earlier leaf removal. The mean degree of polymerisation (mDP) by acid catalysis in the presence of phloroglucinol showed no statistical difference between wines. Conclusions: Early timing of mechanical leaf removal increases proanthocyanidin concentration, but has no influence on the mDP. Increased severity of defoliation and/or higher alcohol levels in the 2008-2009 growing season were responsible for the differences in total tannin concentration compared to the previous year. Significance of the Study: The timing of mechanical leaf removal can influence wine flavan-3-ol concentrations.