Viticultural and Controlled Phenolic Release Treatments Affect Phenolic Concentration and Tannin Composition in Pinot noir Wine

Abstract

Pinot noir fruit is often relatively low in the phenolics important for wine mouthfeel and color stabilization. Previous research has shown that leaf removal can influence the concentration and composition of Pinot noir fruit phenolics, but it is not clear to what extent these effects on grape composition are carried through the winemaking process. A novel thermal treatment, Controlled Phenolic Release (CPR), has been demonstrated to be effective for increasing the phenolic concentration of Pinot noir wines, but there is currently limited information on the interaction between this process and viticultural practices. CPR is microwave heating of grape must to hasten phenolic extraction. This study applied viticultural treatments to Pinot noir (no leaf removal, leaf removal at postflowering and preveraison) in two commercial vineyards (A and B), and winemaking treatments in replicated microvinifications (control, CPR with skin contact, CPR with early pressing) were applied to fruit from vineyard A. Effects on grape and wine phenolics were examined using UV-visible spectrophotometry. Wine tannin composition and polymerization were assayed by methyl cellulose precipitation and high-performance liquid chromatography. Viticultural treatments applied produced significant effects in vineyard A but not in vineyard B. Winemaking treatments affected the concentration of phenolics in wines, but there was no interaction between viticultural and winemaking treatments; effects were additive. Of scientific and practical significance was the finding that grape phenolic concentration determined from homogenate extractions of fruit did not reliably predict Pinot noir wine phenolics. Furthermore, in wines, variation in tannin composition, the extent of tannin polymerization, and tannin size was found between treatments. The novel findings here are that the viticultural treatment and the winemaking treatments were both significant and, being independent of each other, offered two separate ways to adjust phenolics in Pinot noir wine. Viticultural and winemaking treatments were also shown to affect tannin composition, with potential mouthfeel and color stability implications.