The Effect of the timing of leaf removal on berry ripening, flavour and aroma compounds in Pinot Noir wine.

Abstract

In the 2007-2008 and 2008-2009 growing seasons mechanical leaf removal was performed on Pinot noir grapevines at different stages of berry development. Treatments consisted of: no leaf removal (NLR) (control), leaf removal seven days after flowering (LR7), leaf removal thirty days after flowering (LR30) and leaf removal at veraison (LRV). Partial cane removal was performed on all treatment vines in 2008-2009 to reduce crop load variability. The result was a decrease in leaf layer number and interior clusters while an increase in exterior clusters and canopy gaps occurred compared to 2007-2008. In 2008, LR7 resulted in vegetative re-growth. In 2008-2009 all treatments had lower yields per vine compared to 2007-2008 and cluster weight decreased in all treatments in 2008-2009. No significant difference was observed in °Brix, titratable acidity (TA g/L) or pH at maturity, but a significant difference in °Brix between years is reported.

Following the investigation into the reliability and variability of two tannin precipitation assays, the methylcellulose (MCP) assay was performed to determine tannin concentration in the microvinification wines produced from each treatment. Berries from each treatment at harvest were analysed for total tannin concentrations and wines were analysed throughout winemaking including to skins and seeds post fermentation. Tannin concentration in berries at harvest showed no statistical difference between treatments in either year but a statistically significant difference was observed during winemaking and in the bottled wine in both years. LR7 had the highest tannin concentration in the bottled wine in 2007-2008 but LR30 had the highest concentration in 2008-2009 whilst NLR had the lowest in both years. Acid catalysis in the presence of phloroglucinol using liquid chromatography mass spectrometry (LC-MS) showed no statistical difference in the mean degree of polymerisation (mDP) between treatment wines but there was a significant statistical difference between years. The 2009 wines had increased tannin concentrations compared to 2008 and a decrease in mDP of all wines in 2009 was found. Reversed Phase-High Performance Liquid chromatography (RP-HPLC) analysis of flavan-3-ols showed the highest concentration in LR7 wines and a shift from 2,3-cis to 2,3-trans was observed with increased leaf removal.

An aroma method for the identification and quantification of specific “fruity” and “green” volatile aroma compounds was developed using Headspace-Solid Phase Microextraction coupled with Gas-Chromatography Mass-Spectrometry Stable Isotope Dilution Analysis (HS-SPME-GC-MS-SIDA). An increase in both “green” and “fruity” volatile aroma compound concentrations in the 2009 wines occurred compared to 2008. However, “fruity” aromas were above their odour threshold in both years but “green” compounds were below. Sensory analysis consisted of a modified version of free choice profiling (FCP) carried out by a panel of Waipara winemakers. Sensory analysis revealed that NLR wines in 2008 were described as “vegetal’ and leaf removal treatments resulted in wines with a higher intensity of “dark fruit aroma and palate” than wines from non-defoliated vines.

Results suggest that the timing of mechanical leaf removal increases tannin concentration but has no influence on the mean degree of polymerisation (mDP). Increased severity of defoliation and/or higher alcohol levels in the 2008-2009 season were responsible for the statistically significant differences in total tannin concentration compared to the previous year.