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50 WINES&VINES June 2016 GRAPEGROWING PRACTICAL WINERY & VINEYARD C luster-zone leaf removal refers to deliberate removal of selected leaves around grape clusters. It has been widely used in the vineyards of cool-climate viticultural regions to improve air circulation and sunlight exposure as well as decrease disease pressure. 10,44,56 Canopy microclimate is important in deter- mining fruit and wine quality. 18,55 A dense can- opy with inadequate sunlight exposure can result in poor-quality grapes. 34 On the contrary, sunlight-exposed grapes are generally higher in total soluble solids, anthocyanins and phenolics and lower in titratable acidity and malate com- pared to shaded fruit—although climate condi- tions may have an important impact. 7,21,22 Overexposure to sunlight also leads to greater than optimal berry temperature, resulting in fruit sunburn and inhibition of color development. 52 Therefore, determining appropriate levels of leaf removal for optimum sunlight exposure is im- portant for producers to consider when manag- ing vines to yield high-quality grapes. Grape-derived volatile secondary metabo- lites play important roles in fruit and wine aroma quality, since they reflect the particular variety, vineyard, regional climate and soil type. 41 Only a small portion of grape volatile compounds are present in their free forms, and the majority exist in non-volatile, glycosidically bound forms or other precursor forms. 16,59 How- ever, these non-volatile precursors can be con- verted to the volatile form through enzymatic or chemical hydrolysis during vinification and aging, thus contributing to wine aroma. 16,28,29 Little research has been done on volatile composition with leaf removal in red grape cultivars. Many studies investigated the influ- ence of leaf removal on grape-derived terpe- noids of white grape varieties; however, results are still inconclusive. For example, in research conducted in British Columbia (Canada), basal leaf removal increased both free- and bound- form terpenoids in Gewürztraminer grapes. 44 However, research on Riesling has shown only increases in bound-form terpenoids with leaf removal. 45,64 Conversely, in central Europe, wine made from Riesling grapes grown with leaf removal showed no differences in free and bound forms of terpenoids compared to those with no leaf removal, while increases in free- and bound-form terpenoids were observed in Sauvignon Blanc wine by leaf removal. 24 Con- flicting results may be due to vineyard loca- tion, seasonal climate, cultivar, rootstock, timing and severity of leaf removal. The effects of leaf removal on grape-derived C 13 -norisoprenoids have not been sufficiently studied. C 13 -norisoprenoids constitute an im- portant part of the volatile compounds of "neutral" type grapes such as Cabernet Sauvi- gnon, 3 Syrah, 39 Sauvignon Blanc 30 and Pinot Noir. 12 These compounds can be formed by direct degradation of carotenoids, or they can be stored as glycoconjugates that release their volatile aglycone during fermentation via en- zymatic and acid hydrolysis processes. 2,50,59 Sunlight exposure has been speculated to in- fluence levels of C 13 -norisoprenoid in grapes. R. Ristic et al. reported that after acid hydrolysis, Shiraz wine made from shaded fruit had de- creased levels of β-damascenone and 1,1,6-tri- methyl-1,2-dihydronaphthalene (TDN) compared to those made from typically exposed fruit. 46 Other research has reported either an increase or no change of β-damascenone in shaded grapes. 25,27 Fruit-zone shading is a concern in the Pinot Noir vineyards of Oregon's Willamette Valley due to the high vegetative growth common in the region. Excessive vine growth results from the region's ample winter and spring rainfall combined with the high water-holding capacity of soils. Therefore, basal leaf removal is com- monly applied post-fruit set in vineyards throughout the region. However, it is unclear what level of leaf removal is required to achieve optimal quality. A three-year study was designed Leaf Removal's Influence on Pinot Noir Basal leaf removal changes chemical and volatile compositions By Hui Feng, Fang Yuan, Patricia A. Skinkis and Michael C. Qian