# So2 In Wine



## Tim F (21/1/12)

Hey all,

With wine making season nearly here again I've decided I want a better understanding of using SO2 in wine - exactly what it does, when to use it and how much. I want to be able to work these out on the fly as opposed to flipping through crusty old books on the day and trying to convert campden tablets per gallon to ppm etc 

I've spent the day going through a few of my books, reading up online and talking to an organic chemist in the family. I've written up some notes below for myself and think I've wrapped my head around most of it. I know there are some knowledgable winemakers on the forum so if anyone has the time to read through my notes and point out anything that is wrong it'd be greatly appreciated.
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The legal maximum limit for Sulphur Dioxide (SO2) in Australia is 250-300mg/l
Mg/l = ppm

When added to wine, some SO2 becomes bound to other compounds in the wine and some remains unbound. Some bound SO2 is permanently bound to other compounds (aldehydes and proteins), and some forms less stable compounds which may turn back to the free form when the existing free SO2 in the wine is reduced. 

With additions early in the wine making process when total SO2 additions are less than 50mg/L, roughly half of additions remain free and half immediately becomes bound. Later, when total additions are above about 60 ppm, 80-90% of any further addition remain as free SO2.

Free (unbound) sulphur dioxide in wine takes 3 forms: SO2 (referred to as molecular SO2) the sulphite anion (SO32-) and the bisulphite anion (HSO3-). Of these, molecular SO2 has the sole (or at least by far the major) anti microbial action.

When measuring wine, free SO2 (unbound SO2) is usually measured rather than total SO2 (eg bound plus free SO2). The ratio of molecular SO2 to the sulphite anions is determined by the pH of the wine, with a lower pH causing more molecular SO2 to be present.

In a winery actual free SO2 can be measured. In home wine making without being to check how much of the total added SO2 is bound vs free this is more difficult so wine makers may just add small amounts of SO2 (15-30ppm subject to pH) when racking, bottling etc.

SO2 can be added to wine with SO2 gas (or liquefied gas), as sulphurous acid or a solution of SO2 in water, or as salts of SO2 (sodium(Na2S2O5) or potassium(K2S2O5) metabisulphite). Potassium metabisulphite comes as a powder or in 'Campden' tablets. 1 Campden tablet contains 0.5 0.55g of Potassium metabisulphite.

Potassium metabisulphite in practice adds around 50% of its weight in SO2 to the wine. For example adding 10mg of potassium metabisulphite to 1l of wine should give 5mg/L or 5ppm SO2. (As per the chart below, 5ppm SO2 in wine with pH 3.4 would give 0.125ppm molecular SO2 )

A minimum of 0.8 mg/L of molecular SO2 is needed in white wine to stop oxidation/bacterial growth. A figure of 0.4 0.6 mg/L is given for red wine but this may be subject to the condition of the grapes, with 0.825 mg/L needed to kill brettanomyces and wild yeasts. Malolactic fermentation is inhibited when total (free and bound) SO2 exceeds 35mg/L


[codebox]
Wine pH Bisulphite Molecular SO2 Total free SO2 (mg/L) needed to give 0.8mg/L molecular SO2
3.0 94% 6% 13
3.2 96% 4% 21
3.4 97.5%	2.5% 32
3.6 98.5%	1.5% 50
3.8 99% 1% 80
4.0 99.4%	0.6% 130
[/codebox]


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## Greg.L (21/1/12)

That's a pretty good summary, I can't see any errors. A few important points.

SO2 binds to pigments in wine, so isn't as effective in red wine. Red wines usually go through MLF after primary fermentation so so2 isn't added till MLF is finished, it can be hard to decide when MLF is done. (SO2 is added before primary).
The binding to pigments can strip the colour in a rose type wine, but the colour will come back.
The main thing that binds so2 is acetaldehyde, which is produced during primary so at the end of primary there isn't any free left.
If you add too much so2 you can get rid of it by carefully adding hydrogen peroxide.

Greg


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## Tim F (21/1/12)

Cheers, I'll add your points to my notes!

So SO2 at crush > primary fermentation > MLF > more SO2 as needed.


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## pokolbinguy (21/1/12)

Seems pretty good to me. Just not too much pre fermentation otherwise you may have a hard time getting your fermen to start. You can also use small additions, 10ppm or so, to kill off aceto bacter etc during ferments.

Aim for 25+ppm free post MLF to stop bacteria spoilage and oxidation.


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## Greg.L (21/1/12)

If you're doing a slow white wine ferment you can add more a couple of weeks into the ferment for extra protection, but you have to watch your total doesn't get too high because you will still have to add more after the ferment finishes. Reds are fermented much warmer and there's not much point adding till later.


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## pokolbinguy (21/1/12)

Don't add it during a low activity ferment as you could easily cause the yeast to give up the ghost and produce a stuck ferment


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## Muggus (21/1/12)

Seems solid. A few notes from my studies/experience:

- When adding PMS we generally calculated that 68% is SO2, and half of that is free and the other half is bound. For example, adding 100ppm of PMS to a wine will leave you with 68ppm SO2, and half of that, 34ppm is bound and the other free.

- Figures for legal SO2 levels in wine are based on TOTAL SO2 levels...ie, bound + free. Important to note, especially if you're only testing for levels of Free SO2. 250mg/L is for table wines, anything above is for sweet/dessert wines, particularly Botrytis affected wines...pain in the ass! Not a huge issue if it's just for home consumption.

- I've met a few wine makers who co-innoculate yeast and malobacteria. The idea is that the MLB will lie dormant in the must until the yeasties have done their job with the sugars then kick in and finish off the malic acid. Important to note they're pedantic little critters though...temp control is handy.

- Because SO2 tends to bind with anthocyanins, ie colour/tannin molecules, adding it to a red ferment will tend to strip some colour. I'm told this comes back with time...not sure about that, but the powers that be know what they're doing...

- As a general rule, I usually hit a red wine with 80mg/L SO2 post malo, before barrel. Along with topping of barrels, if you do plan extended aging, you should test free SO2's around every 2-3 months. Around about 30mg/L should be alright.

- As your table mentioned, pH is VERY important in wines for effectiveness of SO2, particularly in reds. Around about 3.5 is a good spot to be in, so long as the wine is balanced. Anything over 3.6 and alarm bells should be ringing, especially if you plan to keep it a while. I had the odd problem last year of having a Shiraz with a high Total Acid, but high pH...above 3.6...so rather than acidify with Tartaric as i usually would, I went with food grade Lactic acid...less harsh on the palate than Tartaric. Worked well...good option if something like that happens.


Sorry to bombard you, just a few things to consider.


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## manticle (21/1/12)

Possibly stupid question - will acidifying the wine/must at some point make it more resistant to spoilage and less likely to need addded sulphites?

Been interested in winemaking for some time (have some/most of the required equipment) but not interested in any sulphite additions (headache material).

Cheers and sorry for vaguely OT


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## felten (21/1/12)

I have no idea what I'm talking about other than having read a few wiki articles, but isn't there methods of preservation that don't include so2. Like fortification and extended aging in the barrel to control oxidation.

I'd like to make some fortified wines in this style as well, but definitely don't have the means or knowhow to do it.


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## Muggus (21/1/12)

manticle said:


> Possibly stupid question - will acidifying the wine/must at some point make it more resistant to spoilage and less likely to need addded sulphites?
> 
> Been interested in winemaking for some time (have some/most of the required equipment) but not interested in any sulphite additions (headache material).
> 
> Cheers and sorry for vaguely OT


Yeah it does, and legally you can add different types of acid to meet that need. However, it also has an effect on the palate of the wine, for example, a red wine with too much acid seems quite lean on the palate. 
If you have something like a early picked, cool climate, dry riesling on the other hand, where the pH upon picking might be around the 2.9 mark, you won't need much SO2 to make it an effective antibacterial.




> I have no idea what I'm talking about other than having read a few wiki articles, but isn't there methods of preservation that don't include so2. Like fortification and extended aging in the barrel to control oxidation.
> 
> I'd like to make some fortified wines in this style as well, but definitely don't have the means or knowhow to do it.


Fortification works to a point. The higher alcohols created through the fortication process slow the rate of oxidation and inhibit most bacterial spoilages. However it doesn't prevent it happening, and there are bacteria that will survive such conditions...and a port gone bad in barrel is truely one of the nastiest things out there!


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## Greg.L (22/1/12)

manticle said:


> Possibly stupid question - will acidifying the wine/must at some point make it more resistant to spoilage and less likely to need addded sulphites?
> 
> Been interested in winemaking for some time (have some/most of the required equipment) but not interested in any sulphite additions (headache material).
> 
> Cheers and sorry for vaguely OT



You can make wine at home without so2 because there's no financial risk. If you lose a batch it doesn't matter too much. However all yeast produce some so2 so your wine will still have some, and really I would rather add so2 than acid. So2 is also an anti-oxidant so white wine needs so2 to keep its flavour, unless you can keep air right away. At home it is hard to keep air out so so2 helps with flavour.


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## manticle (22/1/12)

Wine and cider with added sulphites give me a massive headache and feelings of anxiety that I simply do not get when I drink my own beer, most commercial beers, low/no added sulphite wines and my own cider. I realise sulphites occur naturally but those amounts don't trouble me. Obviously it's in conjunction with alcohol - I don't get that from dried fruit for example.

I don't want to overdose the wine with acid but the idea just gives me something extra to play with.

Cheers


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## Muggus (22/1/12)

manticle said:


> Wine and cider with added sulphites give me a massive headache and feelings of anxiety that I simply do not get when I drink my own beer, most commercial beers, low/no added sulphite wines and my own cider. I realise sulphites occur naturally but those amounts don't trouble me. Obviously it's in conjunction with alcohol - I don't get that from dried fruit for example.
> 
> I don't want to overdose the wine with acid but the idea just gives me something extra to play with.
> 
> Cheers


Absorbic acid (vitamin C, E300) is sometimes used as an additional anti-oxidant in white wines. Might be worth a look at.
Your other option is, of course, sparkling wine.


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## manticle (22/1/12)

Cheers muggus.


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## kirem (22/1/12)

Muggus said:


> Absorbic acid (vitamin C, E300) is sometimes used as an additional anti-oxidant in white wines. Might be worth a look at.
> Your other option is, of course, sparkling wine.



Surely you aren't thinking of using ascorbic acid in wine with any FSO2?
Probably be a good idea to check what happens to ascorbic acid in wine without any FSO2.

http://www.awri.com.au/industry_support/wi...cid/Default.asp


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## Muggus (22/1/12)

kirem said:


> Surely you aren't thinking of using ascorbic acid in wine with any FSO2?
> Probably be a good idea to check what happens to ascorbic acid in wine without any FSO2.
> 
> http://www.awri.com.au/industry_support/wi...cid/Default.asp


Hmmm yeah they go hand in hand don't they...almost defeats the purpose. Ah well...

But hey...there's always sparkling wine


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## vinlibervin (23/1/12)

Trying to get my head around the figures for total additions

I have used Kmeta powder for my SO2 additions this year.

A couple of questions concerning calculating the total addition of SO2 - (a) should I only calculate on the basis of 68% of the Kmeta actually becomes SO2 - so adding the SO2 additions and not the Kmeta additions (probably just worked this out for myself ...); 

(B) do you include the addition of Kmeta at crush - in which case how do you take into account lost amounts in racking etc. I know that typically 75% to 80% of must becomes wine but then you have rackings after that = especially after racking off the gross lees where you might lose 10%?

Thanks


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## drsmurto (23/1/12)

What are you making Tim?

I'm thinking of doing a chianti style this year (90% sangiovese, 10% cabernet sauvignon), last one i did (2010) was a super tuscan (50% sangiovsese, 25% cabernet sauvignon, 25% grenache).

If i can repeat the quality of the last batch i will be a happy camper - it was served at my sister in laws wedding a few weeks ago.  

If you want to discuss winemaking, am more than happy to do so over a glass of the 2010 'Deux Monts'.


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## Tim F (24/1/12)

Sounds good! I'll drop you a PM. Might get your opinion on my 2010 Shiraz too.

I'm going to try making a Grange style Shiraz this year, might be a bit ambitious but from what I can figure out it's just good grapes, extended maceration, then 12-18 months in new oak. Should be fun even if it isn't Grange


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## Greg.L (24/1/12)

Tim F said:


> Sounds good! I'll drop you a PM. Might get your opinion on my 2010 Shiraz too.
> 
> I'm going to try making a Grange style Shiraz this year, might be a bit ambitious but from what I can figure out it's just good grapes, extended maceration, then 12-18 months in new oak. Should be fun even if it isn't Grange



How will you know if it tastes like Grange?


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## Tim F (24/1/12)

I'm getting a bottle next month as part of my 'research'


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