sulfur dioxide measurement and management anita oberholster chik brenneman

Sulfur Dioxide Measurement and

Management

Anita OberholsterChik Brenneman

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 (Hydroxy-sulfonates• 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*

pHMolecular

SO2 Bisulfite Sulfite

Free SO2 for 0.825 mg/L molecular

2.7 10.50 89.5 0.00283 7.92.8 8.54 91.5 0.00364 9.72.9 6.90 93.1 0.00467 12.03.0 5.56 94.4 0.00596 14.83.1 4.47 95.5 0.00759 18.53.2 3.58 96.4 0.00964 23.13.3 2.87 97.1 0.0122 28.83.4 2.29 97.7 0.0155 36.03.5 1.83 98.2 0.0196 45.13.6 1.46 98.5 0.0248 56.53.7 1.16 98.8 0.0312 71.13.8 0.924 99.0 0.0394 89.33.9 0.736 99.2 0.0497 112.04.0 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 KMBS0.576

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

• End point seen using starch indicator/redox electrode

• Useful for Free and Total SO2

HISOHISOH 242232

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

OHIHIIO 223 3365

Sulfur Dioxide Measurement and Management

Aeration-Oxidation (Vacuum aspiration)

lug

kondenseerder

wyn

indikator

25% v/v H P O3 4

0.3% H O2 2

• Air Aspiration/Nitrogen sweeping

• SO2 volatilized and bubbled through a peroxide trap

• Sulfuric acid titrated with NaOH

• Useful for Free and Total

42223222 0 SOHHSOSOOH

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?