AVF Proj. ID: 627
Year Funded: 2015
Category: Enology - Tannins Phenolics
Investigators: James A. Kennedy

Improvement of Wine Quality: Tannin and Polymeric Pigment Chemistry

Summary:

Seven vintages of UC Davis Oakville Cabernet Sauvignon spanning 35 years was selected for analysis by a complimentary suite of mass spectrometric techniques.  The vintages from 1974 to 2009 selected by informal sensory evaluation and basic wine chemistry to be of a representative vertical style were: 1974, 1981, 1988, 1994, 2001, 2003 and 2009.  All wines were produced at UC Davis for research purposes and stored in the UC Davis cellar together. This sample was determined to be the most controlled and uniform sample of wines varying by vintage only as could be obtained for the project.  Al basic wine chemistry was obtained, pH, ethanol concentration etc. as were various assays for comparison to mass spectrometric data. 

The following objective were submitted for the grant proposal under which this work was peformed. 1) Observe the evolution of pigmented tannin throughout aging

 

a. Employ our method of complimentary mass spectrometric techniques (ICR, QTOF, QTrap) for comprehensive identification of wine matrix compounds.

b. Observe the changes in relative abundance, depletion and accumulation in pigmented tannin composition (35 Year Vertical)

c. Correlate pigmented tannin structural analysis with well-known molecular characteristics (mDP, mass recovery) and newly developed sensory representative analyses (“grippiness”) to better convey the impact of these discoveries

2) Apply existing synthetic technologies.

 

a. Development of a library of standards for quantitation and calibration.

b. Postulate wine pigment precursors for examination of mechanistic pathways.

c. Employ the standards to quantitate the classes of polymeric pigment in wine.

 

Wine Research Assays

Phloroglucinolysis was performed on the wines used for the study (Table 1) as well as their extracts (Table 2). The mass recovery demonstrates typical value dropping off well below 80% after 7 years. Molecular mass after 50% elution also follows expected patterns of increase with age.  This indicates overall larger tannin in the older wines as supported by McRae et al 2012. The molecular mass is a measure of intact tannins, as opposed to the mDP which measures only those tannins which could be cleaved by phloroglucinol. The inconsistency between these two values is reconciled by the mass recovery, indicating that more complexity of the tannin structure is a factor in the older wines, for instance additional interflavan bonds preventing phloroglucinol attack.

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