# Hop flavour gone after 1 day in keg



## brewermp (11/7/19)

Hey fellow brewers I recently put down a New England ipa in my fermentasauras and finally got to put it in the keg yesterday. 

My high level process was to keep it at 15psi for the whole ferment then cold crash for 24hours and keg it.

When I transferred to the keg in an oxygen free method I then force carbed by turning the pressure up to 30psi. Rolling it then waiting 30 minutes turning down the pressure to serving pressure.

The first glass on the night of kegging was absolutely beautiful. I walked away chuffed. 24hours later my beer has almost no hop aroma. I don’t know what is wrong.

Any pointers?


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## goatchop41 (11/7/19)

Any change to colour or flavour as well? It would be surprising if it oxidized that quickly, even for a NEIPA.

You didn't just have the keg fridge too cold do you? That would obviously completely dull the aroma and flavour.

Lastly, what was your keg transfer method? It is surprising sometimes how some people think that they are doing O2-free transfers, but really aren't.


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## Schikitar (11/7/19)

brewermp said:


> The first glass on the night of kegging was absolutely beautiful. I walked away chuffed. 24hours later my beer has almost no hop aroma.


This happens to me, maybe not after a day but after a week..



goatchop41 said:


> You didn't just have the keg fridge too cold do you? That would obviously completely dull the aroma and flavour.


Curious.. I've not heard this before, what is an ideal temp to have to not affect flavour & aroma?


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## goatchop41 (11/7/19)

Schikitar said:


> Curious.. I've not heard this before, what is an ideal temp to have to not affect flavour & aroma?



It's exactly why substandard adjunct lagers can actually taste alright on a hot day when they come straight from an esky full of ice, or how adding ice to whiskey dulls it (if we exclude dilution of the whiskey).

A cursory google search will give you plenty of answers, including this: https://www.homebrewersassociation.org/how-to-brew/proper-beer-serving-temperatures/


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## Schikitar (11/7/19)

Thanks, pretty sure my fridge is well too cold then (at about 3-4 degrees at a guess), will adjust and see if it improves my situation! Cheers!


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## brewermp (11/7/19)

Thanks for the responses  


I keep my fridge at 3-4c ambient temperature.


Transfer wise my fermentasauras was under pressure, I then put gas in my keg and purged it a couple of times. I then hooked beer lines up, gas hooked up to fermentasauras, spunding valve on keg then started the transfer.


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## peteru (12/7/19)

Agitate your keg to see if it improves once you get all the solids back into suspension.


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## fungrel (12/7/19)

peteru said:


> Agitate your keg to see if it improves once you get all the solids back into suspension.


Why would you want to do that?


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## huez (12/7/19)

fungrel said:


> Why would you want to do that?



I assume because it's a NEIPA. Probably not a bad idea if it's dropped clear. What yeast did you use?

They do oxidise pretty easily, no colour change?


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## brewermp (12/7/19)

WLP4042 - HAZY DAZE IPA BLEND

I’ll try a shake tonight


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## damohb (12/7/19)

Most likely just too cold as already suggested, for NEIPAs I usually follow the +2 rule (ABV + 2, so 7% = 9C, or even a bit higher), and usually find mine improve after coming up from crash temp. If you fermented at 15psi the force carb probably wasn't needed?


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## Schikitar (12/7/19)

brewermp said:


> keep my fridge at 3-4c ambient temperature.


From what I've just learnt in the last day (you can teach old dogs new tricks!) your fridge temp, like mine, is too cold. I reckon mine is between 2-4 degrees, after consulting the various tables I'm going to try 9 degrees as a happy medium for my ales and porters/stouts, give that a run..


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## Dan Pratt (12/7/19)

i find that the first beer, IS ALWAYS the most pungent and most full of flavour., after that as a brewer the overall preception is reduced, maybe its just me. 

One thing i dont do or like with hoppy beers like NEIPA or very hop heavy beers, is force carbonating at 30PSi, i found over teh years this affects hop aromatics, not sure of the science for that but patience and low pressure is best for these beers.


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## MHB (12/7/19)

Following the thread on pressure fermentation, I have spent a fair amount of time this week researching all the literature I can find on the subject.
Will put a copy of one in the footer but basically, there might be some advantages to fermenting Lager under pressure - if your aim is to get the beer out the door ASAP, without too much regard as to flavour. Faster beer not better beer!
When the effect on Ale ferments was examined it became a very different proposition. Anything over ~20kPa (0.2Bar or 3PSI) and the effects are all bad.
I know from experience that highly hopped beers can be damaged very quickly by Oxygen uptake during packaging.
It takes very small amounts to do lots of harm -so perhaps your methods should be reviewed.
Yeast doesn't consume all the O2 in solution, there will always be some unless you take extreme measures to get rid of it, have a look at LoDO brewing techniques. With a normal ferment most of the residual O2 is stripped out by the evolving CO2 - locking in the CO2 locks in the O2 as well - If you really must pressure ferment, don't apply pressure until about half way through your anticipated ferment (CO2 stripes out a bunch of other undesirable volatiles to).
As above the temperature the beer is stored and served at will make a big difference, if you leave it in the glass for a couple of minutes it should come up to temp and some of the flavour will show.
I don't know about shaking the keg, a lot of what form the haze in highly hopped beers may be settling out (or if its hop oils floating to the top), room for some experimentation, got a 10L glass high pressure bottle, will try to get some super hoppy beer into it and see what happens.

I really think pressure fermenting Ale is a loosing proposition (not too impressed with the Lager version either). Making super hoppy beers is a real art, I suspect LoDO is going to be critical, but for gods sake get over the pressure fermentation addiction, it isn't helping.
Mark

PS, this is from 1984, there are several other papers around that have followed on from here. Worth noting that brewing researchers were quite familiar with pressure fermentation 35years ago, it still isn't standard practice or even a common practice, really only Lager factory beers use the process to make beer that I for one home brew to avoid, think about it.
M


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## onemorecell (12/7/19)

Interesting to hear the different opinions on pressure fermenting.
In your reading, did you find any benefits to a small amount of pressure? (ie under 3psi)


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## Schikitar (12/7/19)

Dan Pratt said:


> One thing i dont do or like with hoppy beers like NEIPA or very hop heavy beers, is force carbonating at 30PSi, i found over teh years this affects hop aromatics, not sure of the science for that but patience and low pressure is best for these beers.


Is this where I've heard about carbonic bite? If so, is that influenced noticeably between force carbing and serving-pressure carbing do you think? I'm probably getting off track..



MHB said:


> I really think pressure fermenting Ale is a loosing proposition


Always interested in your educated thoughts MHB, I've been fermenting ales under pressure but really don't think I need to (and I don't brew lagers). The only thing lately I've been interested in doing is capturing the CO2 to the keg that will eventually become the serving keg - effectively just to save on gas.


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## goatchop41 (12/7/19)

brewermp said:


> Transfer wise my fermentasauras was under pressure, I then put gas in my keg and purged it a couple of times. I then hooked beer lines up, gas hooked up to fermentasauras, spunding valve on keg then started the transfer.



Simply purging the keg a few times might not make it as O2-free as you would think.
The ideal method would be to fill the keg with sanitiser, then push it all out with CO2. That way you can be confident that the keg is truly purged of O2. Then rack under pressure using your spunding valve.

But honestly, it does sound like temp of the keg fridge may be the real issue here


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## f00b4r (12/7/19)

This is an interesting read around purging kegs and the effectiveness of different methods.


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## MHB (12/7/19)

Good link foob4r.
Schikitar you need to read that link before doing anything like storing gas. Apart from it being a lot less pure than many might expect (actually having enough O2 in to cause the problem you are trying to avoid), there is also the risk of infection so I would put an HEPPA filter between any stored CO2 and where I wanted to use it.
The reality of brewing is often much more complex than would appear to be the case on first examination. I really think you need to look at the real costs, there are plenty of safe ways to save money, storing CO2 isn't one of them.

If you really want LoDO in package, filling the keg and blowing out with CO2 is really the best option, just don't use an O2 based sanitiser…
Mark


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## Schikitar (12/7/19)

I'll never stop learning with guys like you around, seriously!


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## Smokomark (12/7/19)

MHB said:


> Good link foob4r.
> Schikitar you need to read that link before doing anything like storing gas. Apart from it being a lot less pure than many might expect (actually having enough O2 in to cause the problem you are trying to avoid), there is also the risk of infection so I would put an HEPPA filter between any stored CO2 and where I wanted to use it.
> The reality of brewing is often much more complex than would appear to be the case on first examination. I really think you need to look at the real costs, there are plenty of safe ways to save money, storing CO2 isn't one of them.
> 
> ...


What do you mean O2 based sanitizer. I have been filling my kegs with starsan and co2 purging for a few years now and noticed improvements/better consistincy since.


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## MHB (12/7/19)

Any of the Peroxide based sanitiser or even Sodium Percarbonate (I hope no one would by using that as a final rinse sanitiser).
At work we use Peroxitane to sanitise fermenters before wort is pumped up, home brewers use quite a lot of the shield (peroxide/silver) products, would be pretty silly to use a sanitiser that produces Oxygen when you are trying to minimise O2 exposure.
StarSan isn't peroxide based if that helps.
Mark


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## TheSumOfAllBeers (12/7/19)

goatchop41 said:


> Simply purging the keg a few times might not make it as O2-free as you would think.
> The ideal method would be to fill the keg with sanitiser, then push it all out with CO2. That way you can be confident that the keg is truly purged of O2. Then rack under pressure using your spunding valve.



This.

I remember seeing a report from a us brewery, that the co2 purge only merely diluted the o2 in the keg - you need to use a lot more gas than you think to bring the o2 levels down to something safe.

What’s safe for a lager may not be safe for an NE IPA

Liquid purge is the way to go. You also need to purge your lines


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## Smokomark (12/7/19)

MHB said:


> Any of the Peroxide based sanitiser or even Sodium Percarbonate (I hope no one would by using that as a final rinse sanitiser).
> At work we use Peroxitane to sanitise fermenters before wort is pumped up, home brewers use quite a lot of the shield (peroxide/silver) products, would be pretty silly to use a sanitiser that produces Oxygen when you are trying to minimise O2 exposure.
> StarSan isn't peroxide based if that helps.
> Mark


Cheers Mark, just wanted to confirm I was doing the right thing. Always glad to read your input, thanks for posting so much valuable info.


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## goatchop41 (13/7/19)

Here's the science and numbers when it comes to purging vs racking out sanitiser: http://www.lowoxygenbrewing.com/bre...rging-transferring-stabilizing-finished-beer/


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## Schikitar (13/7/19)

Where do you guys stand on using potassium or sodium metabisulfite when racking beer into the keg? My _impression_ is that it can perhaps reduce levels of any O2 left in the keg/beer upon transfer? I tried to find some more info on that lowoxygenbrewing.com website but there's too much science talk going on for my small brain and I won't pretend to understand it..


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## MHB (13/7/19)

Schiktar, good thought, we had a NEIPA at work that went to shit a lot faster than I was happy with so have been giving this a heap of thought.
Still working through the numbers but will post soon with what I hope will be a simple process to get virtually no O2 in packaging. This process is designed for commercial sized systems but I'll make a Corney keg sized version.
Oxygen is clearly a real "now" issue.
Mark


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## f00b4r (13/7/19)

MHB said:


> Good link foob4r.
> Schikitar you need to read that link before doing anything like storing gas. Apart from it being a lot less pure than many might expect (actually having enough O2 in to cause the problem you are trying to avoid), there is also the risk of infection so I would put an HEPPA filter between any stored CO2 and where I wanted to use it.
> The reality of brewing is often much more complex than would appear to be the case on first examination. I really think you need to look at the real costs, there are plenty of safe ways to save money, storing CO2 isn't one of them.
> 
> ...



The link you posted Mark is going to a bitter recipe request, copy and paste error?


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## goatchop41 (13/7/19)

Schikitar said:


> Where do you guys stand on using potassium or sodium metabisulfite when racking beer into the keg? My _impression_ is that it can perhaps reduce levels of any O2 left in the keg/beer upon transfer? I tried to find some more info on that lowoxygenbrewing.com website but there's too much science talk going on for my small brain and I won't pretend to understand it..



On my completely unscientific, unblinded experiment of n=1, I recently gave it a go. I had read about it and felt lazy when racking an IPA from fermenter to keg, so I chucked half of a crushed campden tablet in to the keg with my gelatin, purged it once with CO2, then racked from the fermenter.
Almost two months later and it's still tasting and smelling like the day that I racked it, and the colour hasn't changed one bit. I've had issues with a couple of NEIPAs oxidising quickly in the past, so I'm definitely going to try it when transferring the next one that I make


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## brewermp (13/7/19)

Circling back now. The shake of the keg did improve the taste but not to original.

I have increased the temp to 10c with +/- 2c. Whilst the taste has improved it is not like it was. I think I am going to put this down to force carbing.


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## peteru (14/7/19)

I've been using sodium metabisuplhite for purging. My method is fairly simple:

Clean keg.
Drain keg well.
Add about 100ml of correctly diluted StarSan style sanitiser.
Seal keg and invert / rotate for a few minutes.
Drain keg well.
Fill keg about 50% with filtered water.
Add 1/4 teaspoon of sodium metabisulphite and gently agitate to dissolve it.
Completely fill keg with filtered water.
Let keg stand around while I get everything else sanitised and ready for transfer from kegmenter.
Just prior to transfer, I use CO2 cylinder to expel all the water from receiving keg into a spare keg.
This purge goes through the same connector that will be connected to the kegmenter and used to transfer beer. This ensures that the interconnect is also purged.
Do a pressure transfer: CO2 cylinder (pressure P+10kPa) --> kegmenter (pressure P) --> recipient keg --> spunding valve (pressure P-10kPa)
My fermentation process has been to keep the airlock (no head pressure) on the kegmenter until the krausen starts to subside (about 2-3 days for ales), then seal the kegmenter and set the spunding valve to about 150-160kPa. That should be giving me around 2.3 volumes carbonation at the 18C fermentation temps. Let it ferment out completely, then cold crash to 2C and hold it there for about 2 days before transfer. Obviously the kegmenter pressure drops at that stage, but it stays pressurised.

I've been using a floating pickup tube for kegmenter transfers. I'm now contemplating also installing a floating pickup tube into the serving keg and doing the pressurised transfers without could crashing and with about one or two points before expected FG. Stick a spunding valve on the serving keg and let it sit next to the kegerator for a week before putting it in the kegerator. I run the kegerator at around 8C.


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## MHB (14/7/19)

f00b4r said:


> The link you posted Mark is going to a bitter recipe request, copy and paste error?


NO no no...I was just saying that the link you posted was a great read and that Schikitar (which I C&P'd) should read it.
Shouldn't and copy peoples name without realising it formes a random link automatically
Sorry for confusion (mine)
Mark


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## goatchop41 (14/7/19)

peteru said:


> I've been using sodium metabisuplhite for purging. My method is fairly simple:
> 
> Clean keg.
> Drain keg well.
> ...




This seems extremely excessive, especially when you can just fill the keg with sanitiser at step three and skip all of the middle bit. Any reason for having such a convoluted process?


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## peteru (14/7/19)

goatchop41 said:


> This seems extremely excessive, especially when you can just fill the keg with sanitiser at step three and skip all of the middle bit. Any reason for having such a convoluted process?



You haven't been paying attention, have you? 

The sodium metabisulphite is there to lower the dissolved O2, thus avoiding the problem that the original poster raised. It's been mentioned only a few posts up, but my approach is different (less severe.)

I would not dump large amounts of sodium metabisulphite straight into the beer - no need when I have a closed system.


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## goatchop41 (15/7/19)

peteru said:


> You haven't been paying attention, have you?
> 
> The sodium metabisulphite is there to lower the dissolved O2, thus avoiding the problem that the original poster raised. It's been mentioned only a few posts up, but my approach is different (less severe.)
> 
> I would not dump large amounts of sodium metabisulphite straight into the beer - no need when I have a closed system.



Seems a bit rude to suggest that, as I have mentioned above that I have tried using SMB myself, and that you're proposing a completely different mechanism of action/use.

How do you propose that this is doing anything more than just filling the keg with sanitiser and then pushing it from the keg with CO2 would in terms of reducing O2 in the beer? Isn't the whole point of adding SMB to _add it to the beer_ in order to limit the dissolved O2 _in the beer_? Therefore adding it to water and then expelling the water would seem pointless, as there would only be a tiny bit of it left in the keg (and diluted, at that) and that would have a negligible effect.


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## Schikitar (15/7/19)

goatchop41 said:


> Isn't the whole point of adding SMB to _add it to the beer_ in order to limit the dissolved O2 _in the beer_?


Yeah, that's my understanding too, it's not to remove O2 from the keg but rather dissolved O2 from within the beer.. :/


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## MHB (15/7/19)

Actually very different issues. Oxygen pickup during brewing does harm (HSA is real) but Oxygen pickup during packaging is very different.
Oxygen picked up on the hot side is mostly pretty well bound up in relatively stable (if Oxidised) compounds.
Dissolved Oxygen in packaging can act like a free radical and just goes around smashing up flavour compounds, then moving on to demolish another and another...

I'm not really a fan of adding Sulfites to beer, if I were brewing super hoppy beers I would consider adding a little (~10ppm) on top of all the other steps to avoid HSA (LoDO Brewing) and take extreme measures to eliminate any O2 pickup during packaging.
Mark

PS - Way too much information - Sulfites in beer: reviewing regulation, analysis and role
M


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## peteru (15/7/19)

goatchop41 said:


> Seems a bit rude to suggest that, as I have mentioned above that I have tried using SMB myself, and that you're proposing a completely different mechanism of action/use.



Sorry, wasn't trying to be rude, hence the wink emoji.

Yes, it is a different approach. I don't want to add the sodium metabisulphite to my beer in any appreciable quantity.



goatchop41 said:


> How do you propose that this is doing anything more than just filling the keg with sanitiser and then pushing it from the keg with CO2 would in terms of reducing O2 in the beer? Isn't the whole point of adding SMB to _add it to the beer_ in order to limit the dissolved O2 _in the beer_? Therefore adding it to water and then expelling the water would seem pointless, as there would only be a tiny bit of it left in the keg (and diluted, at that) and that would have a negligible effect.



I want the sodium metabisulphite to scrub out the dissolved O2 from the purge water. I am also hoping it will scavenge the O2 that is present as an impurity in the CO2 from the cylinder. The beer coming from the fermenter is as oxygen free as it's going to get. I am trying to avoid introducing further O2 during packaging. Given my process, which I described, the main sources of O2 would be the gas in the receiving vessel, any liquid remaining in the receiving vessel and the gas used to expel the beer from the kegmenter. The sodium metabisulphite added to the receiving vessel will neutralise the O2 remaining in the purge liquid and hopefully also the O2 contamination present in food grade CO2 cylinders. That still leaves the O2 impurities in the cylinder CO2 that is used to provide head pressure for the transfer from the kegmenter. At this stage I don't have an answer for that, however I am hoping that the relatively short time and low pressure differential will result in minimal dissolved O2 contribution from that part of the process.

It does not take much dissolved O2 to take off the shine. I'm trying to avoid it as much as I can. It's also one of the reasons why I don't force carbonate and only use just enough cylinder CO2 to provide sufficient pressure to get a pour. I'm even willing to accept a decrease in carbonation over the lifetime of a keg, over having it oxidise.


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## MHB (16/7/19)

Pretty much where I'm up to, the O2 in the bottled gas is the catch point right now.
Getting the O2 out of the keg you are going to fill isn't all that hard.
Come up with a couple of options: -
1/ Fill the keg with Boiling water (DO is practically zero) has the potential to be a bit hazardous, then blow out the keg with bottle CO2. Bare minimum will reduce DO dramatically, just remember boiling water is dangerous and starts to take-up O2 as it cools.
2/ Fill the keg with an O2 scrubbing solution. Unfortunately Sodium Metabisulphite (SMB) in water isn't all that good a scrubber at ambient. It works a lot better hot and at higher pH. Looking at a scrubbing solution made up of SMB and Sodium Carbonate. At 0.1M a Sodium Carbonate solution will be about 11pH, add in enough SMB, heat to about 60oC and fill the keg, leave for 10 minutes or so and blow out.
Heating the scrubbing solution makes it work a lot faster and more aggressively, at 60oC it also lowers the DO in the water by about 2/3 so the scrubbing chemicals have less work to do, also a lot safer than pumping boiling water around.
Pressurise keg to about 100kPa, turn the keg upside down and wait 10 minutes or so, ease the PRV (lowest point in keg) to expel any residual scrubbing solution.

Thinking about it, I wonder if putting a spare keg in the gas line from the bottle to the fridge 3/4 fill with scrubbing solution (fit an air-stone to the dip tube) might cleanup any residual O2 in the bottled CO2.
Mark


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## peteru (17/7/19)

MHB said:


> Thinking about it, I wonder if putting a spare keg in the gas line from the bottle to the fridge 3/4 fill with scrubbing solution (fit an air-stone to the dip tube) might cleanup any residual O2 in the bottled CO2.



I like that idea. It also gives you an option to use a different scrubbing chemical to prevent transferring gaseous SO2. Maybe ascorbic acid would be a good choice. It would also neutralise chlorine, so you could potentially just use tap water in the O2 scrubbing keg.


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## MHB (17/7/19)

Not so sure about Ascorbic Acid, not sure its aggressive enough to ensure that all the O2 would be scrubbed out on the way through. It is used as a component in some industrial O2 absorbers, usually with a catalyst, and I get the impression its fairly slow. Used in some of the little sachets that you find in flat bread and the like, also incorporated into polymer films on the inside of packaging
Tap water brings it s own O2, in fact municipal water is usually aerated as part of its treatment, so boiled water would be a better choice than tap water.
Metabisulphite at low pH isn't in the free SO2 form but in the SO3- form that we want for O2 absorption.
In the following which shows the various species, where it says the SO3 form is irrelevant, its talking about the effect on preserving wine. Beer is mostly in the 4-4.3pH range (at packaging) so over the pH where you start getting free SO2.
Without more evidence I'm sticking to High pH Metabisulphite, cheap enough, easy to do and I'm sure its very effective.
If I were to use a keg in line I think putting an air-stone on the end of the dip-tube would be a very good idea.
Mark


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## Tangle Foot (20/7/19)

Hi Mark,

Think I will set up a keg with the scrubbing solution you mentioned. A couple of questions come to mind. 

1. Due to space limitations in my beer fridge, I thought that I would put the scrubbing keg outside my fridge with the gas bottle in line. Connection would be gas bottle -> scrubbing keg -> through fridge wall -> CO2 manifold -> serving kegs. Does that all seem OK? Is the scrubbing solution likely to be as effective at 20 deg C ambient as at fridge temperature?

2. How long would the scrubbing solution be effective for? Does it function like a buffer solution and thus lose effectiveness as it does the job? Should I replace it every time I put in a new serving keg (once a month for me)? Or maybe every time I replace a gas bottle (once a year)? Or something in between?

Appreciate your thoughts. 

Cheers 
Alex


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## MHB (20/7/19)

I would put it outside the fridge, most chemical reactions happen faster warmer which is what we want to encourage.
That said it is a chemical reaction so the scrubber is used up, question is how fast. Looking at the specifications for CO2 in Australia they mostly say its better than 99.99% CO2, the balance is basically air which is roughly 20% Oxygen.
So 1kg of CO2 would have at most 0.1g of other gases of which 20% may be O2 so 0.02g.
Short answer is that a keg say 3/4 full of scrubbing solution would be more than enough to clean up a whole 6kg bottle of CO2, *IF* it was 100% efficient. Fitting an air-stone to the bottom of the dip tube (one of those carbonator lids would be good to) will make the reaction more likely, slow gas flow rates will be better (normal use) but high flows might let some gas through untreated...
I cant give you a definite answer on how often to change the scrubber, use it carefully (avoid really fast flows of gas)
0.1M sodium carbonate comes to about 10g/L (10.59 if it matters) and about 250ppm of Sodium Metabisulphite is 0.25g/L would be a good minimum, I'd probably double that.
Hope that helps, be interesting to see how it works

Any with access to a really good DO meter? if so I would be happy to supply all the bits and pieces so we can measure the outcomes.
Mark

PS when you buy Sodium Carbonate - watch the hydration, that will change the amount you need.
M


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## 2095brewer (21/7/19)

Goatchop...

All that (very theoretical) work from low oxygen brewing doesn’t recognise the fact that the higher mass and lower temp of CO2 used to purge a keg will make it sink towards the bottom of the keg, no? So when you release via the gas pressure relief valve it will come from the top, hence be higher O2 content. I recognise it is not perfect, but returns aren’t as diminished as they quote in their huge document.

I’m definitely one for ways to improve, but I’d like to see something with some proof rather than hypothetical theories. Love the creative and lateral thinking, but does anyone from a commercial setup that might have some good evidence based advice for us home brewers?

Thanks.


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## peteru (21/7/19)

2095brewer said:


> higher mass and lower temp of CO2 used to purge a keg will make it sink towards the bottom of the keg, no?



No. That is a common misconception. First, you have turbulence and mixing of gasses, then there's diffusion.

You don't end up with a cylinder full of pure CO2 with a thin layer of O2 on top when you let it stand.


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## Coalminer (22/7/19)

2095brewer said:


> Goatchop...
> 
> All that (very theoretical) work from low oxygen brewing doesn’t recognise the fact that the higher mass and lower temp of CO2 used to purge a keg will make it sink towards the bottom of the keg, no? So when you release via the gas pressure relief valve it will come from the top, hence be higher O2 content. I recognise it is not perfect, but returns aren’t as diminished as they quote in their huge document.
> 
> ...



If it did we would all be dead


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## 2095brewer (23/7/19)

No, we aren’t dead because nobody goes and locally releases mass amounts of cold CO2 above you. I’m not suggesting everything in the atmosphere breaks down from it’s % or composition and falls out and layers IAW it’s molecular mass. If you’re near a massive sinkhole/volcanic vent releasing CO2 you probably would die. Quite a few people have. It doesn’t magically instantly mix on release with the total volume of earths atmosphere. It will eventually, I get that. I also didn’t suggest pure CO2 remains by letting it stand to form layers. Your words. I just suggested that complete mixing (as demonstrated by their graph) isn’t a realistic or real outcome. 

So in high local concentrations, short bursts and time frames where it hasn’t had time to warm to ambient temps, or diffuse, you’re saying that it just magically warms and or fully mixes? Why do they bother CO2 purging cans with this method in commercial canning. Are they wasting their time and don’t know what they’re doing? It’s kind of the same philosophy, no?


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