Oxygen Absorbing Caps

[Kai]

I'm familiar with osmosis and diffusion

Then you'll remember that transfer through a semi-permeable membrane can go from an area of lower pressure to one of higher if the difference in osmotic pressure is greater.

 

[zoidbergmerc]

No it's the other way around.

and while you

I never did physics at high school and university

my housemate and I are both currently doing it and you're wrong.

 

[Kai]

No it's the other way around.

What's the other way round, specifically?

my housemate and I are both currently doing it and you're wrong.

So they taught you about beer caps then?

Beer caps allow oxygen ingress, just like PET bottles do.

 

[MHB]

One of the good things about AHB is that it makes me think.

As counter intuitive as it may seem after some further reading there is evidence that O2 can get into bottles via crown seals. If at what would appear to be very slow rates, I haven't really been able to find any evidence that it is going to be an issue � but it can happen.

The research I found mostly referred to Stelvin Closures on on wine bottles.

If anyone has a link to good quality research specifically on beer I would like to read more. Please note that sales brochures extolling the virtues of O2 scavenger caps, published by people who sell them aren't what I mean by research.

MHB

 

[Fourstar]

One of the good things about AHB is that it makes me think.

So the magical O2 at my place isnt so magical anymore?

 

[MHB]

Perhaps not, temperature changes certainly aren't the issue, beer has been found that's over 100 years old, some of it was still quite drinkable, these beers were under cork that we know allows some gas exchange. So I seriously doubt that O₂ uptake is a real issue.
What I can't figure is, when you think that the difference between the CO₂ concentration in a bottled beer and the air outside the bottle and the concentration of O₂ in the air, remembering that its concentration that provides the motive force to move gas through a membrane.

Let's say a beer is carbed to about 4.5 g/L. Air contains about 21% Oxygen, typically air at sea level weighs about 0.0012 g/L, so the Oxygen concentration in the air would be 0.000252 g/L.
So CO₂ should be escaping 17,857 times faster than O₂ is getting in. (rough as guts numbers not allowing for heaps of factors but still a huge difference)
I've drunk 20 year old home brew that was still well carbed and certainly wasn't oxidised.
So yes it's possible but I won't lose any sleep over it.

MHB

 

[Benniee]

So CO₂ should be escaping 17,857 times faster than O₂ is getting in. (rough as guts numbers not allowing for heaps of factors but still a huge difference)
I've drunk 20 year old home brew that was still well carbed and certainly wasn't oxidised.

That's an interesting point. A lot of the discussion is centered around O₂ getting into the container, but not so much on anything leaving the container. My understanding of the physical principal is that gas difussion is a two way street. So considering the greater pressure differential of CO₂ between the container and the surrounding atmosphere you'd expect that to be leaving the conatiner faster than any O₂ would be entering. I'm probably over simplifying things greatly.

You're right though Mark - gets you thinking...

Benniee

 

[Kai]

Perhaps not, temperature changes certainly aren't the issue, beer has been found that's over 100 years old, some of it was still quite drinkable, these beers were under cork that we know allows some gas exchange. So I seriously doubt that O₂ uptake is a real issue.
What I can't figure is, when you think that the difference between the CO₂ concentration in a bottled beer and the air outside the bottle and the concentration of O₂ in the air, remembering that its concentration that provides the motive force to move gas through a membrane.

Let's say a beer is carbed to about 4.5 g/L. Air contains about 21% Oxygen, typically air at sea level weighs about 0.0012 g/L, so the Oxygen concentration in the air would be 0.000252 g/L.
So CO₂ should be escaping 17,857 times faster than O₂ is getting in. (rough as guts numbers not allowing for heaps of factors but still a huge difference)
I've drunk 20 year old home brew that was still well carbed and certainly wasn't oxidised.
So yes it's possible but I won't lose any sleep over it.

MHB

Very well said! That's what I've been trying to get at.

 

[n87]

I bought some of these recently for a Barley Wine that I'm planning on bottling and putting away for a few years.

Upon reading the replies above, I'm starting to wonder if it's worth it. Now I'm thinking of capping a couple of bottles with regular caps and trying them side-by-side in a few years time to see if there's any difference between the two.

Check back here in a couple of years and I'll let you know how it goes

Cheers,
Kris.

So... might I ask how this experiment went?
Maybe a couple of years late....

 

[Bribie G]

In view of your other thread, exactly what I thought as well when I saw this necro.

 

[tallie]

So... might I ask how this experiment went?
Maybe a couple of years late....

Wow, how time flies. Funnily enough, I still have some of that beer, including two stubbies with the different caps. I'll try to remember to dig them out for an upcoming club meeting and see what a few people think.

It's been one or two years since I've tried a beer from that batch. From memory it had aged quite significantly, developing the sherry-like oxidation qualities you'd expect. Some bottles had taken on a bit of clove/spice phenolic flavour, I guess due to picking up some wild yeast while bottling. It might be a bit difficult to see through all of that now to find any differences between the caps.

 

[n87]

Wow, how time flies. Funnily enough, I still have some of that beer, including two stubbies with the different caps. I'll try to remember to dig them out for an upcoming club meeting and see what a few people think.

It's been one or two years since I've tried a beer from that batch. From memory it had aged quite significantly, developing the sherry-like oxidation qualities you'd expect. Some bottles had taken on a bit of clove/spice phenolic flavour, I guess due to picking up some wild yeast while bottling. It might be a bit difficult to see through all of that now to find any differences between the caps.

Look forward to hearing the verdict.

 

[tallie]

I'll try to remember to dig them out for an upcoming club meeting and see what a few people think.

Look forward to hearing the verdict.

TLDR; No noticeable difference in this particular case

Last night I took the two stubbies to the Merri Mashers club meeting. The beers were presented in a blind triangle test among 7 members who had a mix of levels in brewing and judging experience. The tasters weren't told anything about the beer (including the style or age) and asked to identify the different beer, and what their preference was. Only one taster correctly picked the different beer out of the three samples, and out of them, preferred the non-oxygen absorbing cap sample.

Obviously this is a very small sample size, and due to the size of the bottles, tasters only had a small amount to compare, so take it with a grain of salt.

In terms of the beer itself, as I mentioned in my previous post, it has developed quite a lot of complex flavours over the years. A few of the tasters thought the beer was a strong Belgian ale, giving weight to the possibility of a wild yeast contribution. The phenol was more minty to me than what I remembered as spice/clove. The beers also had a noticeable autolysis flavour in the aftertaste (vegemite/meaty). Once I noticed how much yeast and other material had dropped to the bottom of the bottles, this made sense. I think I was more surprised about how much there was of it in the bottle considering that it wasn't bottled conditioned.

 

[Lyrebird_Cycles]

Since this has been resurrected and since oxygen diffusion through polymers was a research interest of mine (some years ago I patented a wine technology which exploited this) I thought I'd add a couple of points to the above.

It is in fact possible to have a polymer barrier which allows oxygen ingress into the container whilst not allowing significant CO2 pressure loss. The two important factors are the relative permeability of the two gasses and the relationship between concentration gradient and the concentration difference which will have a perceptible effect on the beer.

On the first topic, the permeablity of a gas through a polymer depends on the solubility of the gas in the polymer which in turn depends on the polarity of the gas. For a typical non-polar polymer like polythene the solubility for a non-polar gas like O2 is much greater than that for a polar gas like CO2 and thus the permeation rate is also much higher, a ratio of 5:1 is typical.

On the second topic, although the pressure gradient for CO2 is about 10 times higher than that for O2 and thus the CO2 transfer rate would still be twice the oxygen transfer rate given the 5:1 permeablity ratio cited above, a 20 ppm decrease in CO2 concentration would be difficult to detect where a 10ppm increase in O2 concentration would be catastrophic.

Hope this clarifies things a little.

 

[Zorco]

That's amazing LC

 

[n87]

Since this has been resurrected and since oxygen diffusion through polymers was a research interest of mine (some years ago I patented a wine technology which exploited this) I thought I'd add a couple of points to the above.

It is in fact possible to have a polymer barrier which allows oxygen ingress into the container whilst not allowing significant CO2 pressure loss. The two important factors are the relative permeability of the two gasses and the relationship between concentration gradient and the concentration difference which will have a perceptible effect on the beer.

On the first topic, the permeablity of a gas through a polymer depends on the solubility of the gas in the polymer which in turn depends on the polarity of the gas. For a typical non-polar polymer like polythene the solubility for a non-polar gas like O2 is much greater than that for a polar gas like CO2 and thus the permeation rate is also much higher, a ratio of 5:1 is typical.

On the second topic, although the pressure gradient for CO2 is about 10 times higher than that for O2 and thus the CO2 transfer rate would still be twice the oxygen transfer rate given the 5:1 permeablity ratio cited above, a 20 ppm decrease in CO2 concentration would be difficult to detect where a 10ppm increase in O2 concentration would be catastrophic.

Hope this clarifies things a little.

Thanks LC,

Do you have an opinion (researched or otherwise) on the oxygen scavenging polymer used in the caps?
Would be really interesting to see how much oxygen it actually takes out of the equation, and how fast as I have worked out that if you have a perfect (home brew level) bottling process, you are still likely to have ~7ppm oxygen in the headspace
http://aussiehomebrewer.com/topic/94479-how-much-o2-does-the-yeast-actually-consume-in-bottle/