feb 20, 2007so2 and wine 1 dennis henry corkscrew society meeting feb. 20, 2007
TRANSCRIPT
Feb 20, 2007 SO2 and Wine 1
SO2 and Wine
Dennis HenryCorkscrew Society Meeting
Feb. 20, 2007
Feb 20, 2007 SO2 and Wine 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/Winecatalog2006.pdf
● 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 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, 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.
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 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.
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 UseFree SO 2 required for given molecular SO 2 level
pH Free SO 2 ( mg/ l) for given molecular SO 2
level
0.6 mg/ l 0.8 mg/ l 2 mg/ l
2.8 6 9 22
2.9 8 11 27
3.0 10 13 33
3.1 12 16 41
3.2 15 20 51
3.3 19 26 64
3.4 24 32 80
3.5 30 40 100
3.6 38 50 125
3.7 47 63 157
3.8 59 79 197
3.9 74 99 248
4.0 94 125 312
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
S tarting Free Total S O2 pH V olum e of D esired 10 30 3.2 19 0.8
Additions R equired of K M etaB isulphiteTarget Free S O2 M ultip lier Add S O2 m g/l spoons 1/8 tsp gram s
20 2.0 21 36 0.94 0.12 0.7
R equired M olecular S O2S O2 pK a R eds : 0.5 to 0.6 ppm
1.81 in wine D ry W hites : 0.8 ppmS weet W hites : 1.5 to 2.0 ppm
S tart ing Total Free S O2 A ddit ion 0 50% 2.0
50 70% 1.480 90% 1.1
Table of A ddit ion E ffec ts
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 10-20 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 7-11 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 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.
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 $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%)
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 10-
20 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, 0.5304 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.