Sulfur Dioxide
Measurement and
Management
Chik Brenneman
Anita Oberholster
Sulfur Dioxide Measurement and Management
Introduction
• What is sulfur dioxide?
• Why is it important
• Practical considerations for
winemaking/Management during aging
• Measurement techniques
• What does it mean?
• Alternatives
Sulfur Dioxide Measurement and Management
Overview
• Chemical antioxidant and inhibitor
of microbial activity
• Labeling requirements
• Industry wide trend for reduction in
use
Sulfur Dioxide Measurement and Management
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
Sulfur Dioxide Measurement and Management
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
Sulfur Dioxide Measurement and Management
Sulfur Dioxide Species
• Molecular (SO2)
• Bisulfite (HSO3-)
• Sulfite (HSO32-)
Sulfur Dioxide Measurement and Management
Sulfur Dioxide Species
• Molecular (SO2)
• Anti-microbial
• Peroxide scavenger
• Volatile
Sulfur Dioxide Measurement and Management
Sulfur Dioxide Species
• Bisulfite (HSO3-)
• Binding form (Hydroxysulfonates
• Acetaldehyde, acetaldehyde, glucose,
quinones, anthocyanins
Sulfur Dioxide Measurement and Management
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
Sulfur Dioxide Measurement and Management
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
Sulfur Dioxide Measurement and Management
Sulfur Dioxide Measurement and Management
Free and Total Sulfur Dioxide
• Total – Bound = Free
• Exist as a dynamic equilibrium
• Post fermentation goals to add and
stabilize the equilibrium
Sulfur Dioxide Measurement and Management
Practical Considerations
• Understand the relationship with
pH
• Volatility and sensory thresholds
• Balancing acidity independent of pH
Sulfur Dioxide Measurement and Management
Inhibitor of microbial activity
Sulfur Dioxide Measurement and Management
pH versus free sulfur dioxide
The percentage of SO2 forms in solution at specific
pH values*
Free SO2 for
Molecular
0.825 mg/L
pH
SO2
Bisulfite Sulfite
molecular
2.7
10.50
89.5 0.00283
7.9
2.8
8.54
91.5 0.00364
9.7
2.9
6.90
93.1 0.00467
12.0
3.0
5.56
94.4 0.00596
14.8
3.1
4.47
95.5 0.00759
18.5
3.2
3.58
96.4 0.00964
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
Sulfur Dioxide Measurement and Management
Other Practical Considerations
• Cleaning
• Sanitation
• Segregation of blends
Sulfur Dioxide Measurement and Management
Sources of Sulfur Dioxide
• Potassium Metabisulfite
• Powder form
• Effervescent form
• Gas
• Concentration specific solutions
Sulfur Dioxide Measurement and Management
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
Sulfur Dioxide Measurement and Management
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
Sulfur Dioxide Measurement and Management
Sulfur dioxide analysis (free and bound)
•
•
•
•
•
•
Ripper Iodine Titration
Ripper Iodate Titration
Aeration Oxidation
Monier-Williams
Fiastar
FOSS
Sulfur Dioxide Measurement and Management
Measurement Methods
• Each method has its limitations
• Hydrolysis of the hydroxy-sulfonate
can affect interpretation of the free
form
Sulfur Dioxide Measurement and Management
Ripper Iodine Titration
• ReDox titration
H 2 SO3  I 2  H 2 SO4  2 HI
• End point seen using starch
indicator/redox electrode
• Useful for Free and Total SO2
Sulfur Dioxide Measurement and Management
Ripper Iodine Titration
• Limitations
• Iodine degradation
• Starch degradation
• Endpoint recognition
• Interfering compounds
• Polyphenols
• Ascorbate
Sulfur Dioxide Measurement and Management
Ripper Iodate Titration
• Iodate stability
• Iodide-Starch indicator
• Iodine produced in situ
IO3  5I   6H   3I 2  3H 2O
Sulfur Dioxide Measurement and Management
Aeration-Oxidation (Vacuum aspiration)
• Air Aspiration/Nitrogen
sweeping
• SO2 volatilized and bubbled
through a peroxide trap
2
H 2O2  SO2  SO3
kondenseerder
 H 2 0  H 2 SO4
lug
• Sulfuric acid titrated with
NaOH
• Useful for Free and Total
0.3% H2O 2
indikator
wyn
25% v/v H3PO4
Sulfur Dioxide Measurement and Management
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
Sulfur Dioxide Measurement and Management
Monier-Williams
(AOAC sanctioned)
• Set up is similar to A-O
• Sample size consideration
• Reflux is 1.75 hours
Sulfur Dioxide Measurement and Management
Fiastar
•
•
•
•
•
Colorimetric endpoint
High volume throughput
Up to 200 mg/L range of detection
Cost $20-30K
Maintenance is key
Sulfur Dioxide Measurement and Management
FOSS
• FTIR scan of both the liquid and a
gaseous sample.
• Secondary method
• Fast results
• FTIR support on line
Sulfur Dioxide Measurement and Management
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
Sulfur Dioxide Measurement and Management
Alternatives to sulfur dioxide
•
•
•
•
•
•
•
•
Lysozyme
Velcorin
Ascorbic acid
Ozone
Ultrasound
UV light
Low electrical current (LEC)
Pressure
Sulfur Dioxide Measurement and Management
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
Questions?