SO2 Anthony Carone

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SO2Anthony Carone
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Sulfites

• A derivative of sulfur, it is a compound that is
  found mainly in
• Fresh and processed foods such as fruits,
  vegetables
• Wine
• Forms naturally during the same fermentation
  process that turns grape juice into alcohol
• Nearly all wines contain small amounts of
  Sulfites (10 mg/l) regardless of winemakers
  intervention

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Sulfite Use in Wine

• Bleach
• Preserve
• Prevent browning
• Sterilize
• Only Free SO2 has effect on aroma, yeast,
  bacteria, or potential oxidation

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Sulfite Use in Wine (contd)

• Inhibits and kills native yeast and bacteria
• Inhibits oxidative enzymes that cause browning
• Decolorizes anthocyanin pigment
• Interacts with phenols in the competitive
  oxidation
• Delays non-enzymatic browning

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Types of Sulfites

• Potassium bisulfite
• Potassium metabisulfite K2S2O5
• Sodium bisulfite
• Sodium metabisulfite
• Sodium sulfite
• Sulfur dioxide SO2

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Chemistry of Sulfur Dioxide (SO2)

• SO2 ? ? HS03- pKa 1.86
• SO2 known as the molecular form
• HSO3- known as the bisulfite form
• Each form reacts differently based on its own
  specific chemistry

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Molecular Form functions

• Inhibits oxidative enzymes
• Behaves as competitive inhibitor
• Kills wild yeast and bacteria
• Effective hydrogen peroxide trapping agent
• Is volatile and detectable by sensory
• Pungent metallic odor
• Is lost due to its volatility

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Sulfite Hazards

• Respiratory Sensitivity
• People with allergies or asthma may have severe
  reactions
• Severe overuse of Sulfites can cause death i.e.
  salad bar incident salad contained some 2000
  mg/l
• SO2 gas severe skin irritant
• Can cause vitamin B, and E deficiencies

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High levels of SO2 in Wine

• Impart a metallic (tinny) harsh character
• Pungent aroma
• Sharpness in the nose
• Soapy" smell

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How much is within the law?

• EEC rules limits the amount of total SO2 (in
  mg/l)
• Red wines Sugar lower than 5g 175 above this
  225
• Rose/White wines Sugar lower than 5g 225
  above this 275
• Appellation controlled (AOC) 300 to 400
  according to type and appellation
• The amount of Free SO2 is not covered by the
  regulations

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Sulfite Myths

• White wine contains less sulfites than Red? False
• 20 to 30 mg/l free SO2 common in most red wines
• 50 mg/l more free SO2 in white wines
• Over 400 mg/l total SO2 in some Sweet, Ice wine
• (above 300mg/l poses a health risk to humans)
• 250mg/l legal limit in EU
• Drink expensive wine less sulfites? False
• 50 mg/l or more free SO2 required for ageing wine
  
• Drink 3 times more water than wine to avoid
  sulfur headaches? Unproven

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When to add SO2 to Wine
Cold Stabilization
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Adding SO2 at Crush

• General rules
• Healthy vintage, average ripeness, strong acidity
  (pH in the 3.2 to 3.3 range) 3-5mg/l
• Healthy vintage, very ripe, feeble acidity (pH
  in the 3.5 to 3.8 range) 5-10mg/l
• Vintage with Rot (pH also gt 3.8) 10-15mg/l

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Tank/Barrel Aging

• Test SO2 level, adjust based on existing pH level
• Equation can be used for specific cases
• Software Sulfite Calculator just plug in your
  pH and SO2 molecular is calculated

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Amount of free SO2 required to achieve necessary
molecular

• For finished wine pH 3.5 to 4.0 about 45-150 mg/l
  free SO2 necessary for 0.825 mg/l molecular
• Rough estimate of free SO2 can be determined by
  quickly multiplying the fraction of the pH by 100

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Bottling

• General guideline for still wine
• 20 to 30 mg/l free SO2 common in most red wines
• 75-100 mg/l free SO2 common in most white wines

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Methods of determining SO2

• Ripper
• Aeration Oxidation (AO)

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Ripper Method

• Wine industry standard for rapid sulfite analysis
  
• Standard iodine is used to titrate free sulfur
  dioxide
• FREE sulfur dioxide is determined directly
• TOTAL SO2 can be determined by first treating
  the sample with sodium hydroxide (SOH) to
  release bound SO2

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Ripper Method (contd)

• The analysis for free and total SO2 is dependent
  upon the redox reaction
• H2SO3 I2 ? H2SO4 2HI
• The completion of this reaction is signaled by
  the presence of excess iodine in thetitration
  flask which is completed with added starch (blue
  black end point)

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Ripper Method Accuracy (Fair)

• The Ripper titration for total SO2 is accurate to
  7 mg/L
• Volatilization and loss of SO2 during titration
• Highly pigmented wines, this inaccuracy can be
  quite extensive
• Phenolic compounds in red wine react with iodine
  producing a false high reading

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Ripper Test Kits

• CHEMetrics' test can be used with red and white
  wines to measure free SO2
• To determine total SO2, a sample pretreatment is
  available

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Aeration Oxidation (AO) Method

• The volume of 0.01 N NaOH required to titrate
  the acid formed to an end point is measured,
  and is used to calculate SO2 levels
• sulfur dioxide in wine or juice is distilled
  (with nitrogen as a sweeping gas or with air
  aspiration) from an acidified sample solution
  into a hydrogen peroxide trap, where the
  volatilized SO2 is oxidized to H2SO4
• H2O2 SO2 ? S3 H2O ? H2SO4

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Aeration Oxidation (AO) Method

• The volume of 0.01 N NaOH required to titrate
  the acid formed to an end point is measured,
  and is used to calculate SO2 levels
• Overall improved accuracy versus the Ripper method

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Questions?