1. Introduction to Oxidation in Wine Andrew L. Waterhouse Department of Viticulture & Enology University of California, Davis

2. Oxidation Avoidance Traditional limit to wine preservation Current technology can exclude oxygen Wine oxidation - a fault?

3. Manage Wine Oxidation At crush / press –Anaerobic press to hyperoxidation Fermentation –Add oxygen for yeast, reductive aromas Post fermentation/s –Micro-ox, barrels, racking In bottle –Affects flavor development

4. Oxygen Measurement Standard meter –Limit of Detection ~0.5 ppm Orbisphere or other Clark electrode –LOD ~2 ppb Nomasense, Mocon, others –Oxydots, fiber optic measure-contact not needed! 10 ppb –Temperature sensitive!

5. Antioxidants SO 2 Ascorbic acid Glutathione

6. Wine Oxidation Chemistry Oxygen reacts with phenols to yield quinone and hydrogen peroxide Hydrogen peroxide oxidizes ethanol to acetaldehyde

7. Known Oxidation Products Quinones –Thiol adducts –Coupling Products Aldehydes –Acetaldehyde –Glyoxylic Acid (Tartaric Acid product) –Flavonoid coupling

8. Oxidative Changes in Wine Formation of quinones from catechols –React with thiols, SO 2, ascorbate, phenolics Fenton oxidation of alcohols –Formation of aldehydes –Reactions of all other substances

9. Oxygen Reduction Cascade

10. Oxygen Pathway in Wine

11. Sulfur Dioxide and Oxygen Sulfite is the sink for oxidation O 2 + 2 SO 2 2 SO 3 1 mg of O 2 will consume 4 mg SO 2 SO 3 + H 2 O H 2 SO 4

12. Polyphenols are Pro-oxidants Generation of quinone and hydrogen peroxide from dioxygen

13. Nikolantonaki, ACA 660: 102 (10) Blanchard, AJEV 55:115 (04) Catechin + 3-Mercaptohexanol

14. Catechin dimer in model juice Poupard, J Chrom A, 1179: 161 (08)

15. Quinone Options

16. Oxygen Pathway in Wine

17. Peroxide Competition

18. Wine Minor Components

19. Oxidation of Wine Acids (Alcohols) to Carbonyls Pyruvic –Observed in wine –Reacts with anthocyanins to make wine pigments Glyoxylic –Observed in wine –Condenses with flavan-3-ols

20. Aldehyde Pigment Reactions “D-ring” formation by acetaldehyde and pyruvate

21. Alcohol Oxidations with ∙OH Aldehydes known oxidation products

22. Wine Oxidation Aroma and color changes Can be managed –A few key steps need better understanding Many current investigations State of the art and practice today