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 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

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

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

14. Inhibitor of microbial activity

15. pH versus free sulfur dioxide
The percentage of SO2 forms in solution at specific pH values* pH
Molecular SO2
Bisulfite
Sulfite
Free SO2 for mg/L molecular
2.7
10.50
89.5
7.9
2.8
8.54
91.5
9.7
2.9
6.90
93.1
12.0
3.0
5.56
94.4
14.8
3.1
4.47
95.5
18.5
3.2
3.58
96.4
23.1
3.3
2.87
97.1
0.0122
28.8
3.4
2.29
97.7
0.0155
36.0
3.5
1.83
98.2
0.0196
45.1
3.6
1.46
98.5
0.0248
56.5
3.7
1.16
98.8
0.0312
71.1
3.8
0.924
99.0
0.0394
89.3
3.9
0.736
99.2
0.0497
112.0
4.0
0.585
99.4
0.0627
141.0
*Boulton, et.al. Principles and Practices of Winemaking, 1985

16. Other Practical Considerations
Cleaning
Sanitation
Segregation of blends

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

18. 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

19. 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

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

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

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

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

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

25. 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

26. 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

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

28. Fiastar Colorimetric endpoint High volume throughput
Up to 200 mg/L range of detection
Cost $20-30K
Maintenance is key
Chemistry geek: Foss FIAStar Segmented-Flow analyzer
Materials:
- Foss FiaStar Unit(s)
- Autosampler
- Sample vials
Analysis time: 5 minutes per sample, following 1 hour of start-up and calibration
Accuracy:  2% v/v
Hazards: None
Cost: Approx. $15,000 per unit for FiaStar; $10,000 for autosampler unit
Theory and Practice: Flow injection analysis works much like aeration/oxidation, but it is automated and performed on a microscale. Small amounts of sample are aspirated into small-bore tubing, with each sample separated by an air bubble. Pumps move the samples through a system of cartridges, where they undergo a series of reactions. The final reaction combines SO2 with a reagent to form a yellow dye, which is read photometrically and analyzed to calculate an SO2 reading. This method is very accurate, very expensive, and best used in large wineries or labs with high sample throughput. Flow injection analysis can be used for both free and bound SO2; free SO2 analysis requires purchase of one FIASTar unit, while total requires two.

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

30. 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

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

32. 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

33. Questions?