1. Dennis Henry Corkscrew Society Meeting Feb. 20, 2007
SO2 and Wine
Dennis Henry
Corkscrew Society Meeting
Feb. 20, 2007
Feb 20, 2007
SO2 and Wine

2. Information Sources Sulphur Dioxide by Ben Rotter
The Use of Sulphur Dioxide (SO2) in Winemaking by Charles Plant
The Wine Lab Catalog
Winetalk
Feb 20, 2007
SO2 and Wine

3. What is SO2 Sulphur Dioxide is a compound of sulphur and oxygen.
Also commonly referred to as sulphite due to the other forms it takes both as an additive and in the wine.
Sulphite is a natural by-product of yeast and as much as 41 ppm has been recorded in fermentations where no SO2 has been added.
Feb 20, 2007
SO2 and Wine

4. Why Do We Use SO2? Antioxidant
High levels of aldehydes give wine a flat and stale aroma and flavour, an oxidised (or maderized) aroma.
Acetaldehyde is oxidised ethanol, and gives sherry its characteristic aroma.
Most acetaldhyde will be bound by the abundant bisulphite form, so we don't notice the effects of oxidation allowing the wine to retain "freshness" of aroma.
When there is oxygen around, SO2 itself becomes oxidized before phenol compounds in the wine do, and so acts as an oxygen scavenger.
Feb 20, 2007
SO2 and Wine

5. Why Do We Use SO2? Anti-Enzymatic
SO2 destroys oxidases (enzymatic catalysts of oxidation).
It inhibits polyphenoloxidases (PPO) which catalyze oxidative reactions in juice (total addition of 50mg/L SO2 can reduce PPO activity by over 90%).
This will increase the oxygen available to yeast in their growth phase when added pre-fermentation.
Feb 20, 2007
SO2 and Wine

6. Why Do We Use SO2? Anti-yeast Yeast selective Antibacteria
Dissolved SO2 gas, and to a lesser extent the bisulphite form, inhibit yeast.
Yeast selective
Promotes yeast selection by hindering the multiplication of non-alcohol producing yeasts such as apiculates, torulopsis, and candida.
Antibacteria
Lactic bacteria are sensitive to free and, to a lesser extent, bound SO2.
Feb 20, 2007
SO2 and Wine

7. Why Do We Use SO2?
Colour
Reduces enzymatic browning by obstructing polyphenol oxidases (the enzymatic catalysts which cause oxidative browning of juice).
It binds with brown quinones or reduces them back to phenols, reducing browning in wines.
Also causes an increase in the extraction/solvency of anthocyanins and polyphenols from fruit tissues but at normal doses the colour increase is aesthetically insignificant.
Feb 20, 2007
SO2 and Wine

8. Why Do We Use SO2? Fermentation
At low levels of 5-10 mg/l SO2 delays the onset of fermentation but later speeds up the multiplication of yeasts and their transformation of sugars.
Feb 20, 2007
SO2 and Wine

9. How Much to Use John Tummon says:
By ignoring the role that pH plays we commonly over sulphite our white wines and under sulphite our red wines.
When judging amateur wines it is not uncommon to detect high levels of SO2 in white wines; however we rarely encounter this problem with red wines. The reason is that red wines typically have a higher pH than white wines.
Surface molds, browning and wines that do not age well are more common with reds. This can be due to inadequate SO2.
Feb 20, 2007
SO2 and Wine

10. How Much to Use John Tummon says:
About .4 ppm to .8 ppm molecular SO2 is needed.
When judging wines, levels over .8 ppm are commonly detectable depending on the individual judge's threshold.
Feb 20, 2007
SO2 and Wine

11. How Much to Use
When you add SO2 some becomes “bound”, the remainder remains “free”.
The bound portion consists of two parts.
Irrevocably bound compounds with aldehydes and proteins
Less stable compounds that can partly turn back to the free form when the existing amount of free is lowered, or even if temperature is increased
Feb 20, 2007
SO2 and Wine

12. How Much to Use The free portion consists of three parts:
Relatively inactive sulphite (SO3=)
Relatively inactive bisulphite (HSO3-)
Molecular SO2. This is the crucial active portion and its size depends both on pH and the total amount of free SO2.
Feb 20, 2007
SO2 and Wine

13. How Much to Use
Feb 20, 2007
SO2 and Wine

14. How Much to Use General Recommendations
Dry reds: 0.5 to 0.6 ppm molecular
Dry whites: 0.8 ppm molecular
Sweet whites: 1.5 to 2.0 ppm molecular
According to one study, ppm molecular is required to suppress growth of Brettanomyces/Dekkera sp. and Saccharomyces cerevisiae.
The recommended level for sweet whites is a bit high in my opinion. You risk having sulphite detected by a sensitive judge.
Feb 20, 2007
SO2 and Wine

15. How Much to Use
The maximum before the sensory threshold is reached is generally considered to be in the range ppm.
Excessive bound SO2 may give a “chemical” taste
Total SO2 should be limited to about 150 to 200 ppm
Legal limit for total SO2 is 350 ppm in the USA and generally lower elsewhere.
Feb 20, 2007
SO2 and Wine

16. How Much to Use
When the total SO2 additions are low, a significant portion of what is added becomes bound.
As the total additions is higher, less becomes bound and more contributes to the free SO2.
You need to keep good records of SO2 additions.
Feb 20, 2007
SO2 and Wine

17. How Much to Use
There are various recommendations on how to predict how much of the sulphite you add will be free.
Actual behaviour will vary from wine to wine.
The numbers I use are:
For total SO2 of 0 to 50 ppm, 50% becomes free (add twice the desired increase)
For total SO2 of 50 to 80 ppm, 70% becomes free (add 1.4 times the desired increase)
For total SO2 of >80 ppm, 90% becomes free (add 1.1 times the desired increase)
Feb 20, 2007
SO2 and Wine

18. How Much to Use
The molecular SO2 level can be calculated by using this formula:
Molecular SO2 = free SO2 divided by (1 + 10(pH – 1.8))
The value of 1.8 is approximate as it is also affected by alcohol level and temperature
Higher temperature or alcohol will increase free SO2
For example, 68 ppm free SO2 at 0°C => 85 ppm at 15°C and 100 ppm at 30°C
Wines with high SO2 levels can be served cold to hide the sulfurous aroma
Feb 20, 2007
SO2 and Wine

19. How Much to Use
Feb 20, 2007
SO2 and Wine

20. How Much to Use
Feb 20, 2007
SO2 and Wine

21. How Much to Use
Feb 20, 2007
SO2 and Wine

22. How Much to Use
My sulphite calculator
Feb 20, 2007
SO2 and Wine

23. Addition of SO2
The common form of suphite is Potassium Metabisulphite. It comes in:
Campden tablets
These can vary in content by up to 25%
Powder
Potassium metabisulphite is about 57% SO2 by weight
The Potassium form is preferred over the Sodium
Increases the level of potassium in the wine which later helps to precipitate tartrates when cold stabilising.
Some claim that the sodium form can contribute a `salty' flavour to wine.
Feb 20, 2007
SO2 and Wine

24. Addition of SO2
Storage
The powder should be stored in a glass jar with a plastic coated metal lid.
Plastic containers let oxygen through
The SO2 will attack metal
I find that stored like this that even year old sulphite has good strength.
Feb 20, 2007
SO2 and Wine

25. Addition of SO2
Most people recommend adding sulphite as a 10% solution.
Mix 100g of sulphite with enough water to make 1 liter final volume.
The solution can be stored for a while, but will start to degrade when exposed to oxygen.
Makes it easier to measure the amounts.
Make sure to stir it into the wine, it won't mix by itself.
If you can measure the powder accurately, I find that direct addition works well.
Just sprinkle in and stir to mix and dissolve.
Feb 20, 2007
SO2 and Wine

26. Oxidation and SO2 Depletion
Oxygen first combines with certain metallic ion catalysts (such as iron and copper). Later, these oxidised metal ions oxidise tannins, pigments, sulphur dioxide, and possibly acids.
When oxygen is absorbed in excess or too quickly
The metallic ions cannot carry the oxygen.
Oxygen combines directly with ethanol and higher alcohols to form aldehydes.
SO2 can be used to bind with oxygen and prevent aldehyde formation when rapid oxidation might take place (such as during racking or bottling procedures).
Feb 20, 2007
SO2 and Wine

27. Oxidation and SO2 Depletion
With the slow absorption of oxygen in wine, free SO2 is consumed and the level of free SO2 decreases.
Lose around 5 mg/l per month in wines stored in large tanks in cool cellars with small headspaces.
Wines stored in warm cellars with large headspaces often lose mg/l per month, or more.
In bottle depletion is no more than a few milligrams per year.
Feb 20, 2007
SO2 and Wine

28. Oxidation and SO2 Depletion
SO2 depletion increases with an increase in
Temperature
Headspace
Oxygen exposed surface area to volume ratio
Feb 20, 2007
SO2 and Wine

29. Oxidation and SO2 Depletion
Oxygen Saturation Level
The saturation level of dissolved oxygen in wine depends on temperature (it increases with a decrease in temperature) and the alcohol content of the wine (it increases with an increase in alcoholic content).
At 20 C, 8 mg/l is the saturation level, whereas at 0 C it is 11 mg/l.
Thus, the oxygen saturation range in wine is generally mg/l.
Typically takes several days to a week for SO2 to consume all the oxygen in a saturated wine.
Feb 20, 2007
SO2 and Wine

30. Oxidation and SO2 Depletion
A partially filled container of wine with a surface area of 100 cm2 will absorb oxygen at 2 mg/l per hour.
A 19L carboy half full has a surface area of about 450 cm2 so you reach saturation in about 1 hour
Filled to the neck it is about 11 cm2 so it takes about 2 days to reach saturation
To react with 1 mg of oxygen, 4 mg of SO2 is required
Filled to the neck this is 22 ppm of SO2 per day
I find that with a solid bung, a carboy filled to the neck looses SO2 very slowly (only a few ppm per month)
Feb 20, 2007
SO2 and Wine

31. Oxidation and SO2 Depletion
Racking
Gentle rackings often cause an oxygen uptake of 1-3 mg/l (loss of 4-12 ppm SO2)
Those with more turbulence and air exposure might absorb 3-8 mg/l during each racking (loss of ppm SO2).
Barrels
Penetration through oak wood itself is insignificant at 3- 7 mg/l per year.
When barrels are often opened for testing/tasting, oxygen absorption may be around mg/l per year.
Feb 20, 2007
SO2 and Wine

32. SO2 Measurement
Titrets are the most common and are based on the ripper measurement method
Aeration-Oxidation is more complicated and expensive, but more accurate (used by many small- mid sized wineries)
Spectrometers would be nice but are too expensive for even small-mid sized wineries.
Feb 20, 2007
SO2 and Wine

33. SO2 Measurement Aeration-Oxidation Test Kit Reagents: $425 US
Reagents:
Hydrogen Peroxide (H2O2), 30%, dilute to 1% for analysis
A/O Indicator solution
0.01 N NaOH
0.01 N HCl to standardize NaOH
Phosphoric acid (25%)
Feb 20, 2007
SO2 and Wine

34. SO2 Measurement Ripper Method Limitations:
Reacts with phenols, resulting in false-high reading.
As free SO2 is reduced, more is released from bound SO2, again giving a false-high, particularly in reds. Rapid test execution will minimize these reactions.
The dark color of red wines makes it difficult to identify the end point of the titration.
Potential volatilisation of SO2 during titration, test needs to be done rapidly.
Botrytis & ascorbic acid can also give false-high results.
Titrets tend to over-estimate SO2 content by around mg/l (some quote 10 for whites and 20 for reds).
Feb 20, 2007
SO2 and Wine

35. SO2 Measurement Titret Manufacturer's Instructions Snap tip
Put tip in sample and squeeze to draw some in
Wait 30 seconds
Rock to mix
Continue to add and rock until it turns colourless
Feb 20, 2007
SO2 and Wine

36. SO2 Measurement
My Tips
Draw the sample from the carboy and test immediately
Put the tip in the sample before breaking it
Keep the tip in the sample the whole time
Have a strong light to observe the colour
Work quickly through the test
Feb 20, 2007
SO2 and Wine

37. SO2 Measurement Measuring Reds
You can get a reasonable indication of free SO2 by doing two measurements, but accuracy is limited
Do the first measurement as for a white wine
The end point is when the blue hue disappears
Add a few drops of hydrogen peroxide to the sample and test again
The end point is when the colour matches the end point of the first test (hold them side by side)
Subtract the two readings to get the free SO2
Feb 20, 2007
SO2 and Wine

38. SO2 Reduction SO2 is often removed from wine by aerating.
Wine is racked from one vessel to another in a violent manner (with turbulence) to encourage oxygen contact.
This method can be traumatic for a wine, potentially over oxidising and "damaging" its delicacy. However, it remains a simple solution to reducing excessive SO2.
This will remove between 12 and 32 ppm SO2.
If the aim is to reduce SO2 by more, then this method can be used on a periodic basis more than once.
If less, the aerating should be done with less violence.
Feb 20, 2007
SO2 and Wine

39. SO2 Reduction Hydrogen Peroxide (H2O2) can be used to reduce SO2
I consider this method more damaging than racking as the addition of oxygen is very concentrated and would highly oxidize a small portion of the wine before it is mixed through.
Amount of reduction
The molecular weight of SO2 is 64.1 and that of H2O2 is 34.
Therefore, g (1/64.1*34) of H2O2 is required to react with 1 g of SO2
Feb 20, 2007
SO2 and Wine

40. SO2 Reduction Example using H2O2
15 liters of wine has a free SO2 level of 70 mg/l. It is desired to reduce this to 40 mg/l.
The reduction of 30 mg/l (70-40) requires an H2O2 addition of 16 mg/l (0.5304*30).
Thus, the 15 liters requires an addition of 240 mg (15*16) of H2O2.
Using a 3% mass/mass solution of H2O2, 7.9 ml (240/30.3) of the solution needs to be added to the 15 liters for the drop to 40 mg/l.
Feb 20, 2007
SO2 and Wine