SO2 and Wine

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

2. SO2 and Wine Information Sources • Sulphur Dioxide by Ben Rotter • http://www.brsquared.org/wine/Articles/SO2/SO2.htm • The Use of Sulphur Dioxide (SO2) in Winemaking by Charles Plant • http://www.bcawa.ca/winemaking/so2use.htm • The Wine Lab Catalog • http://www.thewinelab.com/_fileCabinet/TECH_INFO/Winecatalog2006.pdf • Winetalk

3. SO2 and Wine 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.

4. SO2 and Wine 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.

5. SO2 and Wine 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.

6. SO2 and Wine Why Do We Use SO2? • Anti-yeast • 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.

7. SO2 and Wine 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.

8. SO2 and Wine 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.

9. SO2 and Wine 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.

10. SO2 and Wine 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.

11. SO2 and Wine 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

12. SO2 and Wine 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.

13. SO2 and Wine How Much to Use

14. SO2 and Wine 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, 0.825 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.

15. SO2 and Wine How Much to Use • The maximum before the sensory threshold is reached is generally considered to be in the range 0.8-2 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.

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. SO2 and Wine

17. SO2 and Wine 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)

18. SO2 and Wine 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

19. SO2 and Wine How Much to Use

20. SO2 and Wine How Much to Use

21. SO2 and Wine How Much to Use

22. SO2 and Wine How Much to Use My sulphite calculator

23. SO2 and Wine 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.

24. SO2 and Wine 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.

25. SO2 and Wine 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.

26. SO2 and Wine 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).

27. SO2 and Wine 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 10-20 mg/l per month, or more. • In bottle depletion is no more than a few milligrams per year.

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

29. SO2 and Wine 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 7-11 mg/l. • Typically takes several days to a week for SO2 to consume all the oxygen in a saturated wine.

30. SO2 and Wine 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)

31. SO2 and Wine 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 12-32 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 40-53 mg/l per year.

32. SO2 and Wine 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.

33. SO2 Measurement • Aeration-Oxidation Test Kit • $425 US • http://morewinemaking.com • 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%) SO2 and Wine

34. SO2 and Wine 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 10-20 mg/l (some quote 10 for whites and 20 for reds).

35. SO2 and Wine 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

36. SO2 and Wine 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

37. SO2 and Wine 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

38. SO2 and Wine 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.

39. SO2 and Wine 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, 0.5304 g (1/64.1*34) of H2O2 is required to react with 1 g of SO2

40. SO2 and Wine 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.