Russell Smithyman

Sensory Impact of Extended Maceration and Regulated Deficit Irrigation on Washington State Cabernet Sauvignon Wines

Irrigation practices such as regulated deficit irrigation (RDI) and winemaking practices such as extended maceration have been experimentally evaluated from a chemical perspective but their impacts on sensory composition and interactive effects merit scientific attention. This study evaluated the sensory impact of extended maceration applied to Cabernet Sauvignon grapes sourced from a vineyard subjected to four RDI treatments: replenishment of 100%, 70%, and 25% of full-vine crop evapotranspiration (ETc) from fruit set until veraison followed by 100% ETc until harvest (labeled 100% ETc, 70% ETc, and 25% ETc, respectively) and 25% ETc from fruit set to veraison followed by 100% ETc from veraison to harvest (labeled 25/100% ETc). Each RDI treatment was replicated four times (n = 4) and made into wine, with two replicates designated as controls (10 day skin contact) and two as extended maceration (30 day skin contact). Wines were evaluated by descriptive analysis with a trained panel (n = 15) and chemical and sensory data were correlated using canonical correlation analysis. Wine-perceived saturation and purple component ratings were highest in 25% ETc wines and were highly correlated with the concentration of flavonols, malvidin- and delphinidin-derivatives, and small polymeric pigments. Fruit-based aroma descriptors were highest in the 25/100% ETc and 70% ETc wines. Extended maceration increased perceived astringency and bitterness, which were in turn correlated with the concentration of flavan-3-ol and oligomeric proanthocyanidins. These results suggest that moderate RDI protocols such as 70% ETc and 25/100% ETc impact positively the fruity aroma component (black and red fruit), whereas extended maceration lowered fruity aromas, possibly due to the masking effect of the oxidized character perceived in these wines.

Deficit Irrigation Alters Grapevine Growth, Physiology, and Fruit Microclimate

A deficit irrigation trial was conducted with field-grown Cabernet Sauvignon grapevines in the Columbia Valley of southeastern Washington. Four irrigation regimes were applied in four replicated blocks to replace various fractions of crop evapotranspiration (ETc) between fruit set and harvest. These treatments were designated ET100 (100% ETc), ET70 (70% ETc), ET25 (25% ETc), and ET25/100 (25% ETc before veraison and 100% ETc thereafter). Leaf water status and gas exchange, canopy growth and microclimate, and yield formation were evaluated over three years. Despite yearly variation in growing season temperatures, irrigation treatment effects were consistent among years. Overall, deficit irrigation did not enhance water-use efficiency. The ET100 and ET70 regimes rarely differed in vine physiology and performance. The ET25 regime, however, strongly limited gas exchange and led to a decline in vine capacity and productivity, suggesting that this degree of water deficit was economically unsustainable. In addition, this treatment was associated with small berries on small clusters, very high fruit-zone sunlight exposure, and elevated cluster temperature. The ET25/100 regime was generally intermediate in vine physiology, growth, and yield components. This treatment resulted in open canopies and small berries without the penalty in vine capacity and yield that was incurred with ET25. Potential effects of water deficit on fruit composition may be related to altered canopy size and microclimate, in addition to decreased berry size.