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Sulfur Dioxide Measurement and Management

Sulfur Dioxide Measurement and Management. Chik Brenneman. Anita Oberholster. Introduction. What is sulfur dioxide? Why is it important Practical considerations for winemaking/Management during aging Measurement techniques What does it mean? Alternatives. Overview.

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Sulfur Dioxide Measurement and Management

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  1. Sulfur Dioxide Measurement and Management Chik Brenneman Anita Oberholster

  2. Introduction • What is sulfur dioxide? • Why is it important • Practical considerations for winemaking/Management during aging • Measurement techniques • What does it mean? • Alternatives

  3. Overview • Chemical antioxidant and inhibitor of microbial activity • Labeling requirements • Industry wide trend for reduction in use

  4. Chemical antioxidant • Inhibitor of browning reactions in juice • Polyphenol oxidase • Cultivar, juice vs. must • Typical additions of 30-50 mg/L • Laccase is minimally affected • Residual laccase activity in wine can cause browning • Participates in binding reactions • Aldehydes, e.g. acetaldehyde • Anthocyanins

  5. Inhibitor of microbial activity • Juice – levels for enzyme inhibition are sufficient for inhibition or significant reduction in native flora • In General • Bacteria are sensitive • Yeast are less sensitive • Sensitivity varies by organism

  6. Sulfur Dioxide Species • Molecular (SO2) • Bisulfite (HSO3-) • Sulfite(HSO32-)

  7. Sulfur Dioxide Species • Molecular (SO2) • Anti-microbial • Peroxide scavenger • Volatile

  8. Sulfur Dioxide Species • Bisulfite (HSO3-) • Binding form (Hydroxy-sulfonates • Acetaldehyde, acetaldehyde, glucose, quinones, anthocyanins

  9. Sulfur Dioxide Species • Sulfite(HSO32-) • Anti-oxidant form • Under wine conditions, this reaction is not favoreddue to the low concentrations present • Peroxide scavenging of the molecular form causes retardation of acetaldehyde formation or browing

  10. Relationship with pH • pH • Measure free H+ ions • pH = -log [H+] • Why is knowing the pH important? • Microbial stability • Effectiveness of SO2 • Molecular SO2 is the form effective against microorganisms

  11. Free and Total Sulfur Dioxide • Total – Bound = Free • Exist as a dynamic equilibrium • Post fermentation goals to add and stabilize the equilibrium

  12. Practical Considerations • Understand the relationship with pH • Volatility and sensory thresholds • Balancing acidity independent of pH

  13. Inhibitor of microbial activity

  14. pH versus free sulfur dioxide

  15. Other Practical Considerations • Cleaning • Sanitation • Segregation of blends

  16. Sources of Sulfur Dioxide • Potassium Metabisulfite • Powder form • Effervescent form • Gas • Concentration specific solutions

  17. Calculating SO2 Additions • KMBS comes as a powder, it is a salt of sulfur dioxide. • 57% is ‘active’ • Potency decreases over time (temperature/humidity) • Example: add 50 ppm to 100 L • (Desired addition (g/L)* volume (L))/0.576= g KMBS • 0.050 (g/L)* 100 (L) = 8.6 g KMBS 0.576

  18. Addition Strategy • First additions for the prevention of and/or at the completion of the MLF • 30 mg/L for whites, 50 mg/L for reds • Test at 2-3 weeks as equilibrium is established • Additional additions are based on free and total results • Something is better than nothing

  19. Sulfur dioxide analysis (free and bound) • Ripper Iodine Titration • Ripper Iodate Titration • Aeration Oxidation • Monier-Williams • Fiastar • FOSS

  20. Measurement Methods • Each method has its limitations • Hydrolysis of the hydroxy-sulfonate can affect interpretation of the free form

  21. Ripper Iodine Titration • ReDox titration • End point seen using starch indicator/redox electrode • Useful for Free and Total SO2

  22. Ripper Iodine Titration • Limitations • Iodine degradation • Starch degradation • Endpoint recognition • Interfering compounds • Polyphenols • Ascorbate

  23. Ripper Iodate Titration • Iodate stability • Iodide-Starch indicator • Iodine produced in situ

  24. Aeration-Oxidation (Vacuum aspiration) Air Aspiration/Nitrogen sweeping SO2 volatilized and bubbled through a peroxide trap Sulfuric acid titrated with NaOH Useful for Free and Total

  25. Aeration-Oxidation (Vacuum aspiration) • Limitations • Carrier gas flow rates should be standardized • Glassware/Condenser requirements • Anti-foam is recommended • Some bound SO2 can be released in the acidification step

  26. Monier-Williams (AOAC sanctioned) • Set up is similar to A-O • Sample size consideration • Reflux is 1.75 hours

  27. Fiastar • Colorimetric endpoint • High volume throughput • Up to 200 mg/L range of detection • Cost $20-30K • Maintenance is key

  28. FOSS • FTIR scan of both the liquid and a gaseous sample. • Secondary method • Fast results • FTIR support on line

  29. Alternatives to sulfur dioxide • Alternatives tend to address single variables • Just say no (more than necessary) • Reacting to ‘real’ number • Clean fruit, good sanitation practices and some tolerance to higher volatile acidity

  30. Alternatives to sulfur dioxide • Lysozyme • Velcorin • Ascorbic acid • Ozone • Ultrasound • UV light • Low electrical current (LEC) • Pressure

  31. Summary • Powerful tool in traditional winemaking • Prize for a better substitute remains unclaimed • Use lends to predicable stability in both opened and unopened bottles of wine

  32. Questions?

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