feb 20, 2007so2 and wine 1 dennis henry corkscrew society meeting feb. 20, 2007

Feb 20, 2007 SO2 and Wine 1

SO2 and Wine

Dennis HenryCorkscrew Society Meeting

Feb. 20, 2007


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


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.


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.


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.


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.


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.


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.


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.


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.


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


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.


How Much to Use


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.


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.


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.


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)


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


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


How Much to Use


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


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.


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.


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.


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).



● 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.



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



● 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.



● 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)


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.


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.


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 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).


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


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


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


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.


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


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, 2007so2 and wine 1 dennis henry corkscrew society meeting feb. 20, 2007

Documents

free so2

ppm molecular so2

mgl so2

inadequate so2

use of sulphur dioxide

excessive bound so2

total so2 additions

so2 sulphur dioxide