High-quality Shiraz wines are produced in the Okanagan Valley of British Columbia, but the crop requires extensive bunch thinning to facilitate maturation. A prebloom and fruit-set leaf removal trial was established to evaluate the effect on crop load, fruit quality, maturation, and wine quality. The four treatments were no defoliation, prebloom removal of four basal leaves, prebloom removal of six basal leaves, and fruit-set defoliation in the fruiting zone. The experiment was a randomized complete block design with five blocks. The training system was bi-lateral, vertical shoot-position, and vines were two-bud spur-pruned. Wines were made using conventional methods with field treatments and replicates maintained throughout winemaking, resulting in 20 wines. Basic composition and phenolics were measured in both fruit and wine. Prebloom leaf removal lowered pruning weights and the number of berries/cluster without impacting berry size or the following year’s bud fruitfulness. Phenolic concentrations increased substantially, and fruit maturation was marginally advanced with six-leaf prebloom removal. Sensory evaluation of the wine was done blind by 16 judges tasting 10 wines twice in a balanced incomplete block design. The panel evaluated intensity of black pepper, red fruit, black fruit, jam/cooked/dried fruit, floral, meat, and vegetative flavor and aromas and astringency, body, and length of aftertaste. Sensory evaluations showed high black pepper aroma with leaf removal at fruit set and elevated black fruit aroma with all leaf removal treatments, while vegetative aroma and flavor was more abundant with no leaf removal. Wines from prebloom leaf removal were more astringent and wines from fruit-set leaf removal were least astringent. The sensory assessment of astringency was supported by a two-fold higher concentration of condensed tannins in the six-leaf prebloom treatment.

Funding Support: British Columbia Wine Grape Council and the Agriculture and Agri-Food Canada AgriInnovation Program