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Old 11-15-2010, 11:14 PM   #1
JNish
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I've heard that sulfites are an excellent anti-oxidant and even Charlie Bamforth has recommended use of sulfites to improve flavor stability. However, as far as commercial breweries go, this idea has not been adopted due to US labeling requirements. Sulfites are used regularly in wine and mead making though.

I am wondering if anyone has used sulfites in their beer? I know potassium metabisulfite can be used for dechlorination and as a sanitizer. But has anyone used it for preventing oxidation in beer? If so, how much and when do you add it?

 
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Old 11-16-2010, 05:50 AM   #2
GilaMinumBeer
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Never heard of it. But I have heard of cinnimon used in beer as an antioxidant.

 
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Old 11-16-2010, 12:45 PM   #3
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Yes, brewers commercial and amateur use sulfites at various points in the brewing process beyond just dechlorination/dechloramination. It is even mentioned in professional texts such as Brewing Science and Practice (Briggs et. al.) where they discuss use of it in stabilizing finished beer. They not that the amount used in usually set by regulation and is, in the EU, 20 mg/L (as SO2) except for cask beer where it can be as high as 50. I presume this would the total i.e. the amount from the addition plus the amount produced by the fermentation.

I know at least one homebrewer who used to add metabite to his boil to reduce color formation.

 
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Old 11-20-2010, 04:11 AM   #4
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Brewers will add <10ppm of a metabisulfite salt. Since this will not require them to declare it's presence on their labels. Realistically you can probably add at least five times that to get the additional benefit. A couple warnings though:

1) Adding a sulfite isn't an excuse to not worry about oxygen pickup. Still use best practice in that regard.
2) It's an antimicrobial as well. So adding it will kill you yeast. i.e. it's a good idea for force carbing, not bottle conditioning.

 
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Old 11-20-2010, 08:57 AM   #5
JNish
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So I would assume that you would add the metabisulfite after fermentation is complete? What is the taste threshold that I should stay under?

 
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Old 11-20-2010, 12:45 PM   #6
ajdelange
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Quote:
Originally Posted by JNish View Post
So I would assume that you would add the metabisulfite after fermentation is complete? What is the taste threshold that I should stay under?
That would depend on your intent. If long term stability in the package is the goal then add when the beer goes into bottle or keg. If your goal is keeping the wort in a reduced state (i.e. shooting for lighter color, more reductones) then it would go into the kettle or mash. If the goal is chloramine reduction, it goes in the brewing water. Or combinations of the above.

 
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Old 11-20-2010, 04:11 PM   #7
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I have some left over from SWMBO's wine....hmmmm

Could you add metabisulfates to a carbed keg?

I just started kegging, and my first transfer may have introduced a little oygen.

 
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Old 12-04-2010, 06:11 PM   #8
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Quote:
Originally Posted by ajdelange View Post
Yes, brewers commercial and amateur use sulfites at various points in the brewing process beyond just dechlorination/dechloramination. It is even mentioned in professional texts such as Brewing Science and Practice (Briggs et. al.) where they discuss use of it in stabilizing finished beer. They not that the amount used in usually set by regulation and is, in the EU, 20 mg/L (as SO2) except for cask beer where it can be as high as 50. I presume this would the total i.e. the amount from the addition plus the amount produced by the fermentation.

I know at least one homebrewer who used to add metabite to his boil to reduce color formation.
Thanks AJ. How much K metabisulfite would I add per gallon (or Liter) of mash water to achieve 20 mg/L (as SO2)? Does it depend on mash pH?
Thanks, Tom

 
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Old 12-18-2010, 05:06 PM   #9
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Tom,

I'm new but this is a question I can answer! Yeah it depends on pH. At lower pH so2 is more effective and you can add less for the same level of protection. Still, at beer and mash water pH you are looking at adding quite a bit of so2 to get a protective amount (typically .8 ppm molecular in wine) in there.

The chemistry of so2 in solution is a little complex, but there are calculators out there that will help you out. Here's one: http://wineadds.com/so2 (I'm a wine guy).

You enter in the amount in gals, the pH, and your desired free so2 (in your case 20 ppm) and it will tell you home much Kmeta to add. When you're done, enter the pH and ppm of so2 into this calc to find out how much molecular so2 you have: http://wineadds.com/so2/molecular

HTH.

 
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Old 12-18-2010, 08:16 PM   #10
ajdelange
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Here's the reply I gave to the question in response to a private message because I never saw this post:

* * * * * * * * * *

Potassium metabisulfite reacts with hydrogen ions to produce sulfur dioxide and water:

K2S2O5 + 2H+ ---> 2K+ + 2S02 + 2H2O

Each mole of K2S2O5 weighs 222.2 grams and produces 2 moles of sulfur dioxide (64.1 grams per mole) weighing 128.2 grams. Thus the requirement for a particular level of sulfur dioxide is 222.2/128.2 = 1.733 grams/gram or mg/mg or oz/oz. Thus for 20 mg/L SO2 you would need 20*1.733 = 34.66 mg metabite per liter.

As hydrogen ion is consumed lower pH is beneficial. Put another way, potassium metabisulfite is the salt of a strong base (potassium hydroxide) so that adding it to water or mash will raise the pH. Mash should have enough buffering capacity to hold the pH low but it would probably be a good idea to check pH if using much metabite.

* * * * * * * * * *

What he was asking is how much sulfur dioxide a given amount of metabite releases - not how it is distributed over SO2, HSO3- and SO3--. According to it's MSDS a 1% solution of sodium metabite has a pH of 4.3 (it's not a basic salt at all!) which is about half way between the pK's of sulfurous acid (and typical of the pH of ales) so the reaction is more like

K2S2O5 + H2O ---> 2K+ + 2HSO3-

Nearly all the SO2 from conversion of metabite will stay as bisulfite. With the first pK of sulfurous acid at 1.81 very little will convert to SO2 (only 0.31%). These tiny amounts are sufficient for biological stabilization of wine (and presumably beer) but the questioner was more interested in the reducing capabilities. Bisufite ion can be oxidized to bisulfate thus reducing something in the process and that is what he is interested in here so it is bisulfate he wants, not what vintners call "molecular SO2".

This is not to say that it isn't pH dependent. As the first reaction shows, where pH is low (H+ available) SO2 is formed. At higher pH (second reaction) it is mostly HSO3-.

 
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