Adding Sodium Metabisulphite to Keg to reduce oxygen

[artichoke]

Hi,

Does anyone do this as a matter of course when they keg? Assuming sound kegging technique, i.e. a CO2 purge and minimal O2 pickup during transfer from fermenter to keg, this would be inexpensive and simple insurance to kill off any remaining O2.

I've seen this mentioned in other threads (for example https://www.homebrewtalk.com/showthread.php?t=587188&page=4) but it otherwise doesn't seem to be a very popular technique and I am wondering why.

Is there any good reason to not add SMB to the keg, assuming the amount added is very small so as not to affect the flavour of the beer?


- Artichoke

 

[mabrungard]

The only concern I have is that you would be adding sulfite to your beer. That might be a problem to some drinkers. Another option is to add ascorbic acid to the keg.

SMB addition to the pre-boiled wort does not result in sulfite in your beer since the thermal activity drives off or converts any sulfite.

 

[ajdelange]

Does anyone do this as a matter of course when they keg?

The UK has regulations in place concerning the maximum amount of bisulfite permitted in UK beers so I assume some or many breweries do this. I have heard of a few home brewers doing it too.

Assuming sound kegging technique, i.e. a CO2 purge and minimal O2 pickup during transfer from fermenter to keg, this would be inexpensive and simple insurance to kill off any remaining O2.

If you are using sound kegging technique there is no need for bisufite as there is no residual O2. Of course in the real world there will be some. I think the best way to scavenge that is to, first be sure there is precious little of it and second to keep some yeast in the keg. This is fine until you have to move the keg. If I need to take some beer to an event I rack some off into a new keg (against CO2 counter pressure).

Is there any good reason to not add SMB to the keg, assuming the amount added is very small so as not to affect the flavour of the beer?

The last one is the catch, of course. Bisulfite is widely used in the food industry to keep stuff in a reduced state and thus prevent browning (and other undesirable) reactions from taking place. But if the pH is lowish, as it is in beer, SO2 is released and this doesn't smell or taste very good plus some people are allergic to it so that they don't, for example, spray it all over the salad bar any more and the Brits have maximum permissible amounts in beers.

The thing that really bothers me about it though is a result of an experiment I did a few years back. It's a reducing agent, right? Ought to reduce any acetaldehyde to ethanol this finishing what the yeast didn't, nes pas? So I tried that. Bisulfite is famous for its ability to form adducts with aldehydes (the two molecules just clump together). In my experiment I found the acetaldehyde flavor was gone right enough but was replaced with the flavor of, I presume, the adduct and that flavor wasn't very good!

So I guess I'd say if you want to add bisulfite to finished beer be careful not to add more than the UK regs allow (in case aunt Tilly is allergic) and second, taste test carefully to be sure you haven't spoiled the flavor. If you don't have acetaldehyde then you shouldn't run into the problem my experiment suggested (and it was a single experiment - hardly an 'investigation'). By storing my beers on the yeast I can drink them after 2 or more years. If you don't store on the yeast bisulfite might help you to get something approaching that (no promises).

Just another comment on the SO2. As beer is acidic it will be released into the beer and some will make its way into the headspace. The rest will, if it doesn't form an adduct, reduce something thereby becoming sulfate ion. That's what you want to happen.

 

[artichoke]

Thanks Martin and AJ for your informative replies.

I think I'll work on improving my kegging technique as a first step, before I mess with additions. After listening to a recent Experimental Brewing podcast, I realize I've been using a bad procedure (fill with beer then purge headspace with CO2) that doesn't effectively eliminate residual O2 from the keg.

I ferment in glass carboys. Supposing I used the following procedure to keg my beers, do you think that this would prevent enough O2 from entering the keg to prevent having to add SMB/Ascorbic Acid/yeast to give the beer more longevity, or are there any obvious problems with my technique? I do not own a DO meter.

1) Fill keg completely with Starsan, pump out the Starsan with CO2 so that only CO2 is left in the keg
2) Open carboy, insert business end of autosiphon into beer
3) Start the siphon, discard the first bit of runnings to make sure that air trapped in the siphon tube doesn't enter the keg.
4) Pop the keg lid, dangle siphon tube into the bottom of the keg and fill. Keep keg opening covered with sanitized plastic wrap to (hopefully) minimize air / O2 ingress into the keg.
5) Attach keg lid, chill and carbonate.

Thanks again guys for your expertise.

- Artichoke

 

[GotPushrods]

1) Fill keg completely with Starsan, pump out the Starsan with CO2 so that only CO2 is left in the keg

2) Open carboy, insert business end of autosiphon into beer

3) Start the siphon, discard the first bit of runnings to make sure that air trapped in the siphon tube doesn't enter the keg.

4) Pop the keg lid, dangle siphon tube into the bottom of the keg and fill. Keep keg opening covered with sanitized plastic wrap to (hopefully) minimize air / O2 ingress into the keg.

5) Attach keg lid, chill and carbonate.



Thanks again guys for your expertise.



- Artichoke

#1 is more complex that it seems but can be done. You have to get every nook under the lid flooded and hope not too much O2 comes out of solution as you pump it out. I do it with 1+ year freshness now.

Unfortunately #4 ruins all the work before. You crack that lid and air diffuses in immediately. Get yourself another liquid disconnect and fill through the post. Open the PRV once flow stars and shut it just before you are done.

 

[Horseflesh]

5 gallons of StarSan is a lot to use up every time you keg, but it seems like it should work.

I'll tell you what has worked for me, though the oxygen police scold me.

When I have a fresh keg full of nothing but air and StarSan foam, I blast it out with a few shots of high pressure CO2. I actually use my Sodastream for this--just stick the "wand" into the keg and mash the button. (This is convenient for me, but if you aren't set up for cheap Sodastream refills I would just get CO2 from your keg gear.)

The keg ends up full of CO2 and fog. I do not know what percent oxygen remains inside the keg after the CO2 blasts, but the CO2 is overpowering if you take a sniff. The interior of the keg also has too little oxygen to sustain combustion, though that only assures us that the oxygen level is less than 16%.

Then I connect my fermenter to the Out post, fill from the bottom, seal the keg and purge a few times.

I am sure this isn't oxygen free transfer, but it seems to be good enough. Though to be honest, I never had any problems when I filled kegs without taking extra steps to minimize exposure to the air, either.

Next time I mess with my scuba gear, I will see if I can test the oxygen level inside the keg during this process. I do have a gadget for that somewhere.

 

[artichoke]

Great advice. I too was a bit concerned about step #4. I will take gotpushrod's advice and attach a beer out disconnect to the autosiphon, fill the keg without cracking the lid and use the PRV to enable the transfer.

That should be sufficiently close to 0 O2 in the keg I would hope. The only other contributor at this point I can think of is air mixing with the CO2 in the carboy, but as it lies above the beer I would think this might not really matter that much.


- Artichoke

 

[TexasWine]

If you really want to eliminate O2 when kegging using the procedure above, your best bet is to prime the keg with a sugar solution, just like you would if you bottled. Then let the keg sit at room temp while the yeast do their thing

Also, don't forget to shorten your gas in tube. If you don't you'll never be able to purge the keg effectively.

 

[kh54s10]

I keep it simple. Siphon the beer into the sanitized keg as gently as possible. Close it up, turn on the co2, burp the pressure relief valve a few times, wait until I have proper carbonation - enjoy the beer. Not once have I noticed any off flavors I would attribute to oxygenation.

 

[ajdelange]

For minumum oxygen in the keg you have to fill the keg completely with something else, replace that with pure CO2 and then push the CO2 out with beer. For many people the 'something else' is CO2 but a few calculations will show you that pressurizing with CO2 itself, even through several cylcles of pressurize, bleed, pressurize... isn't terribly effective. Several people use water as the something else, the problems with that being that it has to be sterilized and deoxygenated (I use steam). Sterilization can be achieved by boiling which also deoxygenates but the water needs to be cooled before it can be practically handled and that, of course, reintroduces oxygen. Now this is a place where you might use metabite. Boil some water, let it stand until it is cool enough (covered to minimize incursion of bacteria and wild yeast), then add some metabite and fill the keg(s) as completely as possible with it. Push as much of the water out as you can with CO2 and counterpressure fill with beer. That second part is important and implies, of course, that you have a sealed fermenter under some positive gauge pressure. This isn't going to work with a carboy. Some metabite will go into the beer but not very much and at least any wild yeast that got into the water while it was cooling will be suppressed.

 

[artichoke]

Good discussion, guys. How much process improvement is really required to keep beer fresh in the keg for ~1 year is really what I'm trying to figure out. I started this thread thinking that SMB may be an easy magic bullet but definitely I have concerns about flavour, allergies etc so would prefer not to if I don't have to.

I've tried the keg and purge method and noticed a degradation in quality pretty rapidly (~ 3 months) which is why I am hoping to get the O2 under control - that method clearly isn't working (well) for me. I know this has been a real issue for me as I was getting competition score sheet feedback "slight oxidation" and "lifeless" on some beers that had been ~6 months in the keg, confirming my own judgement.

Boiling H2O, cooling it, adding sodium metabisulphite filling and purging is really getting complicated. How much residual O2 can there really be if I use Starsan solution to completely fill the keg, and push out all the solution using CO2?

Also, I don't have an enclosed pressure vessel, I use glass carboys. I may be very wrong, but I am skeptical that there is a damaging quantity of O2 in the carboy after fermentation and right after I pop the airlock that would get into the beer - - the siphon is submersed in the beer when transferring of course, and the carboy should contain mostly CO2 I would think. I understand that air will mix in with the gasses in the carboy when the transfer is happening, but how much of that air has O2 will make it into the beer? How many ppm's of O2 in the beer from this step can we be possibly be talking about here?

I tried kegging yesterday as per GotPushrod's advice, from carboy into a completely purged keg through the beer out post, opening the PRV valve as I went. My biggest issue with this technique is that I can't see the level in the keg so I don't really know when to stop filling it (beer was room temperature). This is an easily solvable problem though.

- Artichoke

 

[techbrau]

The worlds best and most modern breweries can't even make a beer with complete shelf stability for 1 year.

By spunding in the keg, I can hit about 5-6 months.

 

[ajdelange]

... thinking that SMB may be an easy magic bullet but definitely I have concerns about flavour, allergies etc ...

It just might be your magic bullet. Experiment to find out where the taste threshold is, use half that and see how long the beer lasts.

I've tried the keg and purge method and noticed a degradation in quality pretty rapidly (~ 3 months)... ~6 months in the keg, confirming my own judgement.

How much residual O2 can there really be if I use Starsan solution to completely fill the keg, and push out all the solution using CO2?

Enough to oxidize your beer in 3 - 6 months. It really doesn't take much.

Boiling H2O, cooling it, adding sodium metabisulphite filling and purging is really getting complicated.

Nobody said this was an easy solution. Purging with steam isn't easy either but it works (as long as the beer is lagered/stored on the yeast).

How many ppm's of O2 in the beer from this step can we be possibly be talking about here?

I think we should be talking ppb.

My biggest issue with this technique is that I can't see the level in the keg so I don't really know when to stop filling it (beer was room temperature).

The parenthetical statement sort of indicates that you already know what I'm about to mention here but in case you don't, you can judge the level of the beer in a keg by feeling with your hand where the boundary between stainless and cold beer and stainelss and CO2 inside lies.

I really strongly suggest racking when there is a lot of yeast in suspension. Having a layer of yeast on the bottom of the keg will keep the beer fresh for a year easily. Yes, it is a PITA (sorry, I don't have any easy solutions) if you have to move the keg but it does solve the problem.

 

[wobdee]

I've been adding smb to my kegs for about a year now. After some trial and error I settled in at 10mg/l.

 

[jddevinn]

For minumum oxygen in the keg you have to fill the keg completely with something else, replace that with pure CO2 and then push the CO2 out with beer. For many people the 'something else' is CO2 but a few calculations will show you that pressurizing with CO2 itself, even through several cylcles of pressurize, bleed, pressurize... isn't terribly effective. Several people use water as the something else, the problems with that being that it has to be sterilized and deoxygenated (I use steam). Sterilization can be achieved by boiling which also deoxygenates but the water needs to be cooled before it can be practically handled and that, of course, reintroduces oxygen. Now this is a place where you might use metabite. Boil some water, let it stand until it is cool enough (covered to minimize incursion of bacteria and wild yeast), then add some metabite and fill the keg(s) as completely as possible with it. Push as much of the water out as you can with CO2 and counterpressure fill with beer. That second part is important and implies, of course, that you have a sealed fermenter under some positive gauge pressure. This isn't going to work with a carboy. Some metabite will go into the beer but not very much and at least any wild yeast that got into the water while it was cooling will be suppressed.

Hey AJ,

Have you ever posted anything on your steam generator/method? This is on my "to do list" and the only things I have seen posted are the old steam infusion systems from flyguy and Yuri_Rage.

 

[artichoke]

Hi Wobdee,

In your experience, how is the SMB dosing rate you use working out for you in terms of beer longevity and flavour impact (due to SMB)?

In addition SMB additions, Do you do anything fancy when kegging to minimize O2 uptake, for example closed CO2 transfers from fermenting vessel to keg?

Thanks.

- Artichoke

 

[wobdee]

Hi Wobdee,

In your experience, how is the SMB dosing rate you use working out for you in terms of beer longevity and flavour impact (due to SMB)?

In addition SMB additions, Do you do anything fancy when kegging to minimize O2 uptake, for example closed CO2 transfers from fermenting vessel to keg?

Thanks.

- Artichoke

Nothing fancy here, just Co2 purge a sanitized keg and gravity feed from fermenter to keg.

I do smaller 2.5 gal batches so my kegs don't last more than a month or two, but before I was adding smb I could tell I was losing the freshness and aromas mid way through, now it's good to the last drop.

 

[TexasWine]

I've been adding smb to my kegs for about a year now. After some trial and error I settled in at 10mg/l.

Are you spunding your serving keg?

 

[wobdee]

Are you spunding your serving keg?

Nope

 

[ajdelange]

Have you ever posted anything on your steam generator/method? This is on my "to do list" and the only things I have seen posted are the old steam infusion systems from flyguy and Yuri_Rage.

I'm sure I have but in a nutshell my system is based on a 300,000 BTU/h (input) steam boiler which heats HLT, mash tun, and decoction vessel/kettle with steam coils in 55 gal stainless steel drums. When I had a guy come around to see about installing it he asked if I were setting up to do crabs the reason for this being that he was part owner of a crab house that used the same boiler. I told him "no, beer" but that put the bee in my bonnet that one could draw off steam (through a culinary steam filter) and use it for other purposes, such as crabs (I do steam crabs and sausages with the system) and keg sterilization. For normal use the boiler runs between 5 and 10 psig and that's fine for sterilization. I run a line from the output of the culinary filter to a coupler with pea and check valve removed. The keg is inverted so steam goes up the spear and condensate runs out the gas port. Throttling the outlet (gas) line keeps the steam pressure (and temperature) up in the keg and uses less steam.

After 15 min. I shut the steam off and immediately put on CO2. As the remaining steam in the keg condenses CO2 rushes in to replace it so you start with steam at 5 - 10 psi and wind up with CO2 at 20 - 30 psig. The thought is that 15 minutes flushing with steam will displace most of the air. The fact that I can enjoy beer brewed over 2 years ago suggests that the theory is largely valid. No, the beer isn't as fresh as it was in its prime but the symptoms of oxidation are amazingly small. Keep in mind that this is in no small measure due to mu inclusion of lots of yeast when the beer is kegged.

 

[artichoke]

Sorry to resuscitate this thread, but I've been thinking about using SMB to mitigate keg oxygenation more and more these days.

What I am not clear on though and don't know how to calculate is the theoretical amount of SMB that should be added per ppm of disolved O2 to eliminate the O2 in the kegged beer. I am hoping the chemistry experts can help answer the following pointed questions before I go the empirical route.

1) Suppose I did a keg purge (push out startsan with CO2) and transferred from a glass carboy into the keg through the beer out post. Does anyone have a reasonably close ballpark estimate, or better yet some measured data as to how much disolved O2 might make it into the kegged beer? 10's of ppb? 100's of ppb?

2) How much SMB is required to neutralize 1 ppb of O2 in 1 L of beer?

Thank you,

- Artichoke

 

[techbrau]

1) can vary greatly, because each shotglass worth of air that comes in contact with your beer or is trapped in the keg will add over 200 ppb. IME what you describe has given me 400-800 ppb in the keg. It is not a very effective method for a multitude of reasons, including the facts that air is very hard to get out of your transfer lines, little hiding spots in the keg posts, dip tube, under the lid, etc. There's also the problem that the sanitizer you push out of the keg has dissolved oxygen in it already, unless you take steps to degas it as well. That DO that rapidly comes out of solution and goes into the headspace of the keg as you push it with CO2 due to the fact that the partial pressure of oxygen in the airspace is zero. You're basically vacuuming the DO out of the sanitizer into the keg airspace as you push it. On top of that all, chances are that your CO2 source is not pure enough. Even food grade (99.9% pure) CO2 will contain enough oxygen to add several hundred ppb DO to your beer if you use it to force carbonate. The brewing textbooks like Kunze recommend at least 99.997% pure CO2 for force carbonating. So you can see how all of these sources of oxygen really start to add up...

2) the stoichiometry is about 5:1 (I.e. 5 ppb sulfite reduces 1 ppb oxygen). However keep in mind that sulfite is in competition with everything else in the beer that can oxidize so if you want to protect the beer you need significantly more sulfite than that. 10-15 ppm sulfite in the finished beer is about right, and some will be produced by the yeast too.

IME you are better off racking to your keg with active yeast and about 4 gravity points of fermentable sugar, and naturally carbonating in the keg. Active yeast are the most effective oxygen scavenger you have, and will eat up practically every last bit of oxygen you pick up within literally minutes. Done properly, this technique will net you the lowest oxygen level in the kegged beer that you can hope to attain because the DO level of fermenting beer is basically zero.

By "done properly" I mean:

1) Racking with enough still-active yeast in suspension. Ideally you should rack with about 10-15 million cells per ml. For me, the appropriate amount of yeast makes the beer look clear in the transfer line but a bit cloudy when in a glass.
2) Not racking with too much yeast. If you rack with a majority of the primary yeast, you're going to get terrible results. Do not carry sedimented yeast over into lagering - only carry those cells still in suspension.
3) Racking with fermentable sugar to keep the yeast going
4) Doing at least a simple purge of the receiving vessel before racking (but it doesn't need to be perfect by any means)
5) Filling the receiving vessel completely, so there is little to no airspace remaining.

If you miss your window to rack, you can add 8-10% or so krausen beer when racking. Don't wait too long to do this though, because as soon as CO2 production stops in your primary, oxygen will find a way in and begin oxidizing your beer as it sits in the fermenter. Dormant yeast don't scavenge oxygen.

 

[rabeb25]

By "done properly" I mean:

1) Racking with enough still-active yeast in suspension. Ideally you should rack with about 10-15 million cells per ml. For me, the appropriate amount of yeast makes the beer look clear in the transfer line but a bit cloudy when in a glass.
2) Not racking with too much yeast. If you rack with a majority of the primary yeast, you're going to get terrible results. Do not carry sedimented yeast over into lagering - only carry those cells still in suspension.
3) Racking with fermentable sugar to keep the yeast going
4) Doing at least a simple purge of the receiving vessel before racking (but it doesn't need to be perfect by any means)
5) Filling the receiving vessel completely, so there is little to no airspace remaining.

With following these procedures, I am able to get unreadable (by my DO meter) results in finished beers.
What Tech forgot to mention is doing a traditional cold lager fermentation with a true Bavarian yeast strain is going to generate and retain a lot of yeast derived fermentation sulfites. This is also going to aid and protect the beer in transfers and into serving (with the unpure co2), so I would add that to the list above as well.

Here is a post fermentation sulfite reading of a Helles Export.

Here is the same beer when going into serving (after lagering).

Beer like this will keep brewery fresh for easily past 9 months, my guess is 12+, but I don't have beer this old yet.

 

[jddevinn]

With following these procedures, I am able to get unreadable (by my DO meter) results in finished beers.
What Tech forgot to mention is doing a traditional cold lager fermentation with a true Bavarian yeast strain is going to generate and retain a lot of yeast derived fermentation sulfites. This is also going to aid and protect the beer in transfers and into serving (with the unpure co2), so I would add that to the list above as well.

Here is a post fermentation sulfite reading of a Helles Export.

Here is the same beer when going into serving (after lagering).

Beer like this will keep brewery fresh for easily past 9 months, my guess is 12+, but I don't have beer this old yet.

The dissolved O2 is used up in the reactions with the beer. It will provide a zero reading after this despite the mount of ingress.

 

[rabeb25]

The dissolved O2 is used up in the reactions with the beer. It will provide a zero reading after this despite the mount of ingress.

Thats not true at all...I have many DO readings from this point in other beers with varying DO numbers, based on methods used.