Dennis Henry

1
SO2 and Wine

• Dennis Henry
• Corkscrew Society Meeting
• Feb. 20, 2007

2
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/W
  inecatalog2006.pdf
• Winetalk

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.

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.

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.

6
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
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
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
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
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
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
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
How Much to Use
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, 0.825 ppm molecular is
  required to suppress growth of Brettanomyces/Dekke
  ra 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
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.

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 gt80 ppm, 90 becomes free (add
  1.1 times the desired increase)

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 0C gt 85 ppm at
  15C and 100 ppm at 30C
• Wines with high SO2 levels can be served cold to
  hide the sulfurous aroma

19
How Much to Use
20
How Much to Use
21
How Much to Use
22
How Much to Use

• My sulphite calculator

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.

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.

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.

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).

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

28
Oxidation and SO2 Depletion

• SO2 depletion increases with an increase in
• Temperature
• Headspace
• Oxygen exposed surface area to volume ratio

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

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
  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 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)

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

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

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

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

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.

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, 0.5304 g (1/64.134) of H2O2 is
  required to react with 1 g of SO2

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 (0.530430).
• Thus, the 15 liters requires an addition of 240
  mg (1516) 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.