Oak and Grape Tannins: The Trouble with Tannins J. Harbertson Washington State University
Barrel Aging O 2 ph Heat Oak Tannins Grape Tannins The Aging Process Wines get Less Astringent as they age?
The Aging Process: Influence of Chemical Factors Barrel Aging O 2 leads to production of acetaldehyde HSO 3- binds acetaldehyde SO 2 <->HSO 3 - Equilibrium favors HSO 3 - Oxidation Reactions effected by ph and temp. ph More alkaline -> favors oxidation ph 3.5-4.0 More acidic -> favors breakdown precursors, hydrolysable bonds Heat Controls rate of reaction 48-52F slow, 53-62 faster
The Aging Process: Oak Tannins Hydrolysable Tannins Ellagitannins Minor Tannins (10-100 mg/l) ph, Temperature Origin Barrel Oak Chips Etc.
Gallic Acid Oak Tannins Ellagic Acid Castalagin Castalagin does not directly contribute to astringency of wine Syngeristic effect with wine tannins
The Aging Process Breakdown to release glucose? 1/6 of MW is glucose Rough Guess 100 mg/l ~16.6 mg/l glucose Does not contribute to sweetness Tannic Acid
The Aging Process: What happens? Conversion of ellagitannins into monomers Contribution to Astringency? Not likely Wine gets less tannic not more tannic; do they have different mouthfeel? Tannic Acid Salivary Protein Binding Very ineffective compared to grape tannins Possibly less astringent tannin? Breakdown is problematic
Grape Tannins Condensed Tannins Main Tannins found in Wine Origin Skins (0.5-1.2 mg/berry) Seeds (3.0-4.0 mg/berry) Temperature, ph, O 2 What happens during aging?
The Aging Process: Grape Tannins Reaction(s) with anthocyanins Reaction(s) with acetaldehyde Polymerization? Depolymerization? What do we know?
The Aging Process: Grape Tannins Electron Rich Electron Deficient Depending on ph electrophilic or nucleophilic nature of compound will drive reaction
Grape Tannins: Depolymerization High [catechin] and Low [polymers] leads to formation of smaller polymers Researchers argue wine has this composition
Grape Tannins: Polymerization Aldehydes can cross-link flavanoids Polymer Formation Lots of different combinations found in wine Remember sulfur dioxide (bisulfite) must be used up in order to produce acetaldehyde Less astringent than equivalent size tannin Viticulture & Enology Program
Pigmented Tannins TANNIN-ANTHOCYANIN ANTHOCYANIN-TANNIN Formation of A-T or T-A polymers Bound anthocyanin appears to be a capping unit Evidence: Analytical methods for breaking down tannins cannot break T-A
So what happens? Many of the chemical reactions described will happen but how much depends on you what you are starting with and what you are doing.
Examples Topping up and maintaining 10-20 ppm free SO 2 slows polymerization reactions but does not affect pigmented tannin development. High ph slows pigmented tannin development but along with low SO 2 and oxygen exposure drives oxidative polymerization. Both lead to development of derived tannins that lower astringency. Remember aroma of wine
Conclusion Oak tannins breakdown during wine aging Astringency Contribution (less or more)dubious Condensed tannins do several different types of reactions during aging Reactions with anthocyanins and polymerization contribute to loss of astringency Research necessary Wine Writers currently tell us how long to age wines!
Acknowledgements Juan Munoz-Oca Wine Advisory Committee Eileen and Ash
Wine Science Viticulture & Enology Program
Wine Science Viticulture & Enology Program
Wine Science Viticulture & Enology Program
Wine Science Viticulture & Enology Program
Wine Science Viticulture & Enology Program