Shower Thoughts on Brew Science

[frithy]

Some random thoughts:

• Everywhere says the pressure of an active fermentation keeps oxygen and infections from getting in during brewing, but why wouldn't the carbonation pressure also prevent oxidation in plastic PET bottles? Is there any evidence at all that carbonated PET bottles get oxygenated?

• The environment is full of microorganisms. Without laboratory grade control, every single beer is definitely heavily infected. Before the advent of the modern yeast industry, the entire process would have been incredibly biologically diverse. Yet, beer has been with us since prehistoric times and all around the world in every environment. So, is it possible that obsessive sanitation is all pointless and the only true problem is exposure to oxygen?

 

[day_trippr]

With respect to the first question, don't know who "everywhere" is that speak with such conviction but "they" are more wrong than correct. The presence of carbon dioxide/carbonation has no effect on oxygen ingress through a permeable barrier. See "partial pressure gas laws". And PET is oxygen permeable, just at a much lower rate than most plastics, so one can be assured that oxygen is making it to the beer.

As for the second question...I'm gonna simply go with "No."

Cheers!

 

[frithy]

With respect to the first question, don't know who "everywhere" is that speak with such conviction but "they" are more wrong than correct. The presence of carbon dioxide/carbonation has no effect on oxygen ingress through a permeable barrier. See "partial pressure gas laws". And PET is oxygen permeable, just at a much lower rate than most plastics, so one can be assured that oxygen is making it to the beer.

As for the second question...I'm gonna simply go with "No."

Cheers!

So, I read Dalton's partial pressure gas laws, but can't find where they relate as to how pressure asymmetry affects permeability. You're saying that only the partial pressure of oxygen affects whether oxygen is drawn or repelled from the vessel and not the total pressure? If that's the case, wouldn't the PET vessel holding anaerobic beer work as an oxygen sponge as it has a lower oxygen saturation than the external environment to start?

As for your second response, are you saying beer didn't, couldn't even, exist previous to modern sanitary practices? I'd like to understand.

 

[day_trippr]

You're saying that only the partial pressure of oxygen affects whether oxygen is drawn or repelled from the vessel and not the total pressure?

A specific gas seeks to equalize its pressure on both sides of a permeable "membrane" - ala your PET plastic. Doesn't matter what the specific pressure is of any other gases on either side, they are irrelevant. So, yes, your anaerobic beer "sponge" is a victim waiting for oxidation to happen. It's just a matter of time - and the availability of oxygen outside the bottle, of course.

2nd...I just can't get into a rational discussion based on a hyperbolic scenario - stating "every single beer is definitely heavily infected" isn't drawing me in. Yes, things we didn't intend to get into our beers do get in to varying degrees - including not at all at the one end and heavily infected at the other. Meanwhile, oxidation occurs at varying levels - from not at all through utter dumpster. I don't see why one should concentrate on solving one and not the other...

Cheers!

 

[ebbelwoi]

PET plastic has a rate of oxygen permeability that's only slightly lower than glass. It's so low that tests have shown that there is more oxygen exchange from the interface between the bung and the neck of a glass carboy than there is through the wall of a PET carboy!

https://www.frasermillsfc.com/blogs...=PET plastic has a rate,wall of a PET carboy!

 

[frithy]

A specific gas seeks to equalize its pressure on both sides of a permeable "membrane" - ala your PET plastic. Doesn't matter what the specific pressure is of any other gases on either side, they are irrelevant. So, yes, your anaerobic beer "sponge" is a victim waiting for oxidation to happen. It's just a matter of time - and the availability of oxygen outside the bottle, of course.

2nd...I just can't get into a rational discussion based on a hyperbolic scenario - stating "every single beer is definitely heavily infected" isn't drawing me in. Yes, things we didn't intend to get into our beers do get in to varying degrees - including not at all at the one end and heavily infected at the other. Meanwhile, oxidation occurs at varying levels - from not at all through utter dumpster. I don't see why one should concentrate on solving one and not the other...

Cheers!

Wouldn't the attempted effusion of the pressurized CO2 be capable of clogging the channels the oxygen travels through? Wouldn't the oxygen ends of the molecule lead to this?

For the second issue, all beer is infected with unwanted organisms. There is no side of the spectrum that is sterile save desired yeast. Even the labs churning out packets of yeast can only guarantee a threshold; they can't eliminate it. As for why to not attempt to solve this issue, I'd say selection. The yeasts we have now are able to out-compete other microbes as a result of our selective pressure. The less pressure, the more deviant the future yeast lineages become. With perfect sterility, we'll create weak yeasts incapable of life outside of a lab. Over time, we'll relegate brewing further from the hands of amateurs.

 

[day_trippr]

PET plastic has a rate of oxygen permeability that's only slightly lower than glass.

And?
It's not zero, so it's still inevitable that oxygen gets through.

As for the above: too weird...

Cheers!

 

[AlexKay]

Some random thoughts:

• Everywhere says the pressure of an active fermentation keeps oxygen and infections from getting in during brewing, but why wouldn't the carbonation pressure also prevent oxidation in plastic PET bottles? Is there any evidence at all that carbonated PET bottles get oxygenated?

Yep, there's certainly a question of where "everywhere" really is.

Professionals worry both about loss of carbonation and ingress of oxygen in PET bottles; it's why they're not in common use. As far as permeability of the plastic goes, the oxygen goes in and the CO2 out, with each gas ignoring the other.

If you leave a fermenter full of CO2 alone, then even if oxygen makes its way in, it will take a good long while to diffuse far enough to reach the beer. If you've got convection or other air movement, though, you're right screwed.

Living yeast in the fermenter and their decarboxylases go a long way to mitigating the effects of oxidation.

• The environment is full of microorganisms. Without laboratory grade control, every single beer is definitely heavily infected. Before the advent of the modern yeast industry, the entire process would have been incredibly biologically diverse. Yet, beer has been with us since prehistoric times and all around the world in every environment. So, is it possible that obsessive sanitation is all pointless and the only true problem is exposure to oxygen?

Keep in mind that yeast has evolved to take advantage of a food source, which means keeping bacterial growth under control. It uses both pH and alcohol to accomplish this. So yes, there are other organisms present in almost all circumstances, but as long as you have a healthy colony of yeast outnumbering the "bad" bugs by enough, your product is pretty much what you want it to be.

 

[Zambezi Special]

Also keep in mind that the beer that was around in the past was most likely very different from what is around now.
Very hit & miss and very often low alcohol beers.
Beer was drunk instead of water as the water was so contaminated due to open sewers that it was considered undrinkable.
Obviously, this is what I read as I wasn't around at that time

As for pet bottles: I use them and they do well for me.
At least for shorter time periods. Never had a beer sit longer than 2 months.
I have some 3 month old cider though, sitting to be used for cider vinegar. I'll check later on if that is still carbonated

 

[Silver_Is_Money]

@Zambezi Special, are you talking about the pre-1800's here?

 

[Miraculix]

Yep, there's certainly a question of where "everywhere" really is.

Professionals worry both about loss of carbonation and ingress of oxygen in PET bottles; it's why they're not in common use. As far as permeability of the plastic goes, the oxygen goes in and the CO2 out, with each gas ignoring the other.

If you leave a fermenter full of CO2 alone, then even if oxygen makes its way in, it will take a good long while to diffuse far enough to reach the beer. If you've got convection or other air movement, though, you're right screwed.

Living yeast in the fermenter and their decarboxylases go a long way to mitigating the effects of oxidation.

Keep in mind that yeast has evolved to take advantage of a food source, which means keeping bacterial growth under control. It uses both pH and alcohol to accomplish this. So yes, there are other organisms present in almost all circumstances, but as long as you have a healthy colony of yeast outnumbering the "bad" bugs by enough, your product is pretty much what you want it to be.

In Germany, pet bottles are used heavily within the cheaper beer market. All the discounters have their house beer which usually comes in clear plastic bottles. Sorry....

 

[AlexKay]

In Germany, pet bottles are used heavily within the cheaper beer market. All the discounters have their house beer which usually comes in clear plastic bottles. Sorry....

Ok, but "used in the cheaper beer market" does not contradict my larger point, which is that permeability makes PET inferior to glass. (Permeability of the sealing material on the crown cap is a problem for the latter, though.)

My understanding is that most beer is also packaged in PET in Africa.

 

[Miraculix]

Ok, but "used in the cheaper beer market" does not contradict my larger point, which is that permeability makes PET inferior to glass. (Permeability of the sealing material on the crown cap is a problem for the latter, though.)

My understanding is that most beer is also packaged in PET in Africa.

Pet is inferior, I agree. For smaller time frames it works well, used it myself for years. But as soon as you hit two or three months, oxidation starts to show it's face. Haven't had this with glass.

 

[AlexKay]

Pet is inferior, I agree. For smaller time frames it works well, used it myself for years. But as soon as you hit two or three months, oxidation starts to show it's face. Haven't had this with glass.

I should also revise the "not in common use" statement, because plastic kegs are becoming the norm in the EU. Super-high-tech PET with barrier layers and such, though. And kegs can have a shorter shelf life and still be commercially feasible.

Check out Faq - Dolium one-way kegs, in particular "what is the O2 intake and the CO2 loss?" part, which directly addresses the OP's question: does oxygen migrate in at the same time CO2 migrates out?

 

[Miraculix]

I should also revise the "not in common use" statement, because plastic kegs are becoming the norm in the EU. Super-high-tech PET with barrier layers and such, though. And kegs can have a shorter shelf life and still be commercially feasible.

Check out Faq - Dolium one-way kegs, in particular "what is the O2 intake and the CO2 loss?" part, which directly addresses the OP's question: does oxygen migrate in at the same time CO2 migrates out?

Now I remember seeing these big plastic one way kegs in Poland. They seem to work very well.

 

[Zambezi Special]

My understanding is that most beer is also packaged in PET in Africa.

Not in Southern and East Africa...
Returnable glass bottles for locally produced beer. Disposable glass for imported.
Cans are becoming more common.

What is in plastic is things like chibuku and shake shake. Sometimes in cartons.
This is non-clear beer, low alcohol. Looks a bit like a milkshake Chibuku Shake Shake - Wikipedia

 

[shetc]

Today's podcast from Brulosophy:
Episode 274 | Using PET Kegs For A Pale Lager

 

[NSMikeD]

A side note on PET. There are plastic fermentors that can support higher psi than glass or stainless steel (due to overall design and liabilities issues I would guess and not just because of using PET). The higher pressure speeds up the fermentation time. Since time is the ally of O2 I can see the advantage the reduced time in the fermentor with regard to O2 and unwanted microorganisms. And all this hit me before I jumped in the shower

 

[Miraculix]

A side note on PET. There are plastic fermentors that can support higher psi than glass or stainless steel (due to overall design and liabilities issues I would guess and not just because of using PET). The higher pressure speeds up the fermentation time. Since time is the ally of O2 I can see the advantage the reduced time in the fermentor with regard to O2 and unwanted microorganisms. And all this hit me before I jumped in the shower

Higher pressure does not speed up fermentation time.

 

[VikeMan]

• Everywhere says the pressure of an active fermentation keeps oxygen and infections from getting in during brewing,

Fermentation "pressure" per se (i.e. the PSI pressure itself) doesn't keep out oxygen and bugs. But the "wind" from large amounts of gasses blowing off and flowing out can interfere with O2 and bugs entering.

• The environment is full of microorganisms. Without laboratory grade control, every single beer is definitely heavily infected.

No. Every beer is definitely contaminated. But most are not "heavily" contaminated. Inoculation rate matters.

You're saying that only the partial pressure of oxygen affects whether oxygen is drawn or repelled from the vessel and not the total pressure? If that's the case, wouldn't the PET vessel holding anaerobic beer work as an oxygen sponge as it has a lower oxygen saturation than the external environment to start?

Certainly the net movement of O2 between an O2 free pet bottle of beer and the outside atmosphere is into the bottle. But PET has a only a moderate permeability, and the thicker it is, the less permeable it is. That said, glass is better.

Wouldn't the attempted effusion of the pressurized CO2 be capable of clogging the channels the oxygen travels through? Wouldn't the oxygen ends of the molecule lead to this?

Not really. Occasionally an O2 molecule will richochet off a CO2 molecule, but nowhere near often enough (or directionally precisely enough) to prevent O2 from getting in. It sounds like you're sort of advocating for a special case of the mostly mythical CO2 Blanket.

Higher pressure does not speed up fermentation time.

Quite correct. In fact, the opposite is true.

 

[frithy]

From the Dolium Keg website. It doesn't say what the medium is which is troublesome, but let's assume it's not a live medium, such as unpasteurized beer, actively creating antioxidants. So... why is the oxygen dropping? If the effusion, and attempted effusion, of co2 through the microscopic pores is responsible and is leading to blockage of the channels, it would fit the graph perfectly:

After adding the medium to the vessel, there is a steep increase in oxidation as ambient o2 rushes in to equalize its partial pressure.
However, the even larger force of co2 attempting to escape leads to blockage of channels and also a microscopic "wind" of co2 pushing o2 away.
Meanwhile, as the channels become ever more blocked, the o2 in suspension is removed through reactions with the the medium leading to an ever decreasing saturation of o2.

Anyway, I'd love to hear other users' opinions explaining the rise and then fall in o2. The fact that it rises before falling seems to support my contention.

 

[frithy]

Not really. Occasionally an O2 molecule will richochet off a CO2 molecule, but nowhere near often enough (or directionally precisely enough) to prevent O2 from getting in. It sounds like you're sort of advocating for a special case of the mostly mythical CO2 Blanket.

I'd disagree with one point in particular: why wouldn't it be directionally precise? If you fill a balloon with water or air and then prick a hole, the air is very much unidirectional in its movement out of the balloon. In-fact, the smaller the hole and the larger the pressure, the more precise the movement becomes. You can take your household shower head and see the same dynamic in action. If co2 is escaping from the vessel through microscopic pores, I find it very hard to imagine it wouldn't behave similarly. Why wouldn't it?

 

[khannon]

I'd disagree with one point in particular: why wouldn't it be directionally precise? If you fill a balloon with water or air and then prick a hole, the air is very much unidirectional in its movement out of the balloon. In-fact, the smaller the hole and the larger the pressure, the more precise the movement becomes. You can take your household shower head and see the same dynamic in action. If co2 is escaping from the vessel through microscopic pores, I find it very hard to imagine it wouldn't behave similarly. Why wouldn't it?

In my best George Tekai voice "Oh, My"... Brownian motion for one.

 

[frithy]

In my best George Tekai voice "Oh, My"... Brownian motion for one, but setting that aside, molecules are probably much smaller than you think they are,

The brownian motion would be caused by the collision of escaping co2 and the ambient outside air which is exactly the point being made. *facepalm.

 

[VikeMan]

From the Dolium Keg website. It doesn't say what the medium is which is troublesome, but let's assume it's not a live medium, such as unpasteurized beer, actively creating antioxidants. So... why is the oxygen dropping? If the effusion, and attempted effusion, of co2 through the microscopic pores is responsible and is leading to blockage of the channels, it would fit the graph perfectly:

The graph does fit real life perfectly, but it has nothing to do with gasses clogging microscopic pores.

Beer (pasteurized or not) is full of "antioxidants" in the sense that there are many compounds ready and willing to be oxidized. That's what stales beer. What you're seeing in that graph is the ramp up in dissolved oxygen, being fed from a headspace initially containing a lot of O2. Happening at the same time is oxidation, which happens at a slower pace than the oxygenation for a while (try not to confuse oxygenation with oxidation), because there is still a lot of O2 in the headspace. As the rate of oxygenation slows (because the headspace O2 feeding it is decreasing), the oxidation reactions begin to outpace it, causing point-in-time dissolved O2 to decrease gradually, until there is very little dissolved O2 left.

 

[AlexKay]

Fermentation "pressure" per se (i.e. the PSI pressure itself) doesn't keep out oxygen and bugs. But the "wind" from large amounts of gasses blowing off and flowing out can interfere with O2 and bugs entering.

To pick a nit, not so large amounts. Diffusion constants for gases in air are ~0.1 cm^2/s. So if I'm calculating this correctly, you need something on the order of magnitude of a 1 cm/s wind.

Not really. Occasionally an O2 molecule will richochet off a CO2 molecule, but nowhere near often enough (or directionally precisely enough) to prevent O2 from getting in. It sounds like you're sort of advocating for a special case of the mostly mythical CO2 Blanket.

I agree with "mostly" mythical. "Occasionally" is actually "rather often." Mean free path for molecules at atmospheric pressure is ~70 nm ... which is why the diffusion constant is pretty low (and why diffusion rates are orders of magnitude slower than effusion into vacuum.) If you could open your fermenter somehow without inducing air currents and mixing (you can't), you'd have a few minutes before O2 would start to get into your beer.

 

[VikeMan]

I'd disagree with one point in particular: why wouldn't it be directionally precise? If you fill a balloon with water or air and then prick a hole, the air is very much unidirectional in its movement out of the balloon. In-fact, the smaller the hole and the larger the pressure, the more precise the movement becomes. You can take your household shower head and see the same dynamic in action. If co2 is escaping from the vessel through microscopic pores, I find it very hard to imagine it wouldn't behave similarly. Why wouldn't it?

I said that the occasional collision between an O2 molecule and a CO2 molecule would not generally be directionally precise. They will hit each other at random angles. Sometimes it will be head on, in such a way that a CO2 molecule sends an O2 molecule directly back from where it came, but usually not. And often there will be no collision at all, because there's no CO2 molecule "waiting" in the prefect trajectory to make it happen.

Your analogies include a lot of force. Diffusion of gasses through membranes don't.

 

[AlexKay]

View attachment 813229
From the Dolium Keg website. It doesn't say what the medium is which is troublesome, but let's assume it's not a live medium, such as unpasteurized beer, actively creating antioxidants. So... why is the oxygen dropping? If the effusion, and attempted effusion, of co2 through the microscopic pores is responsible and is leading to blockage of the channels, it would fit the graph perfectly:

It's actually kind of weird that the oxygen drops. If this were a simple system -- air/plastic/beer -- the amount of oxygen entering the beer per unit time doesn't ever change, while the reaction rate of the oxygen in the beer drops over time as oxidizable molecules react. If I had to make up a story as to why the data don't look like that, I'd come up with something about the oxygen already dissolved in the plastic and the barrier layer(s).

What's clear is that once your dissolved oxygen has reached a level over 100 ppb (30 days or so), the fact that it drops afterwards does not mean good things are happening to your beer.

 

[AlexKay]

If the effusion, and attempted effusion, of co2 through the microscopic pores is responsible and is leading to blockage of the channels, it would fit the graph perfectly:

Permeability of polymers isn't, in most cases, because of the presence of microscopic pores, but rather involves solvation of gases into the plastic followed by diffusion through it. If it were pores then net flow (~1 cm/s) of CO2 outward would keep O2 from coming in. Instead, what you have to argue is that there are a limited number of molecular-scale voids in the material to accommodate dissolved gas molecules, and that these voids can be filled with CO2. I've done a little bit of reading of the literature, and there is indeed evidence of this for some polymer systems (the technical way to say this is that the diffusion process is non-Fickian) -- but that only means that the O2 permeability is affected by the CO2, not that it is shut off completely.

But in this case, the Dolium graph provides experimental evidence that O2 is getting into carbonated beer sealed inside the package.

 

[VikeMan]

To pick a nit, not so large amounts. Diffusion constants for gases in air are ~0.1 cm^2/s. So if I'm calculating this correctly, you need something on the order of magnitude of a 1 cm/s wind.

I haven't done the math, but I'd call it large (in comparison to what's not happening in a nearly static post fermentation fermenter).

If you could open your fermenter somehow without inducing air currents and mixing (you can't), you'd have a few minutes before O2 would start to get into your beer.

You are right. You can't open a fermenter without making gas currents. But I wonder how "momentarily" effective a theoretical headspace full of undisturbed CO2 (at a pressure of roughly one atmosphere) would be at preventing O2 ingress, because it only needs to get into the headspace. Once that happens, it can take work its way through the CO2 "blanket" at its leisure.

 

[VikeMan]

But in this case, the Dolium graph provides experimental evidence that O2 is getting into carbonated beer sealed inside the package.

I think the graph shows the intial headspace O2 dissolving into the beer over time, offset by oxidation. I don't think it demonstrates anything one way or the other about the rate of O2 through the package walls, because that effect is swamped by what's happening during the time covered by the graph. If they continued measuring until point-in-time dissolved O2 stopped decreasing, that could indicate something about how fast O2 is getting in.

 

[frithy]

Vikeman, AlexKay, thank you both tremendously. I was just trying to find whether permeability of PET would require pores or could work like a liquid and then AlexKay gave an answer. Then, I wanted to use Vikeman's argument on there being oxygen in the headspace as a possible rebuttal to the experiment showing o2 ingress, but he beat me to it.

An interesting experiment would be to simply take a few PET bottles of a liquid that changes colour when oxidized and add some some yeast and sugar. Then, as a rough control, add the yeast but not sugar to some other bottles of the same liquid. After a few months, see if there is a difference.

Or, even better, use a co2 tank instead of priming to make it far clearer whether it was the co2 that was responsible.

Hell, doing both would be the most telling as it could possibly show some additional benefits of priming vs forced carbonation.

 

[Miraculix]

I've used to squeeze out any air of a beer filled pet bottle, closed it without air inside and let it carbonate naturally with priming sugar. 2-3 months later, oxidation was clearly detectable.

 

[mac_1103]

An interesting experiment would be to simply take a few PET bottles of a liquid that changes colour when oxidized and add some some yeast and sugar.

Knock yourself out.

 

[frithy]

Shower thought:

• Were all historic beers more or less what we now call sours? Was all leavened bread sourdough? How could they not be? Are modern traditionally made farmhouse ales all a bit sour? Are maltøl and kaimiškas sour? hmmm

edit - historic meaning before the 19th century.

 

[mac_1103]

Were all historic beers more or less what we now call sours?

Maybe eventually, but probably not if consumed fast enough.

Was all leavened bread sourdough?

Doubtful since the leavening process is different. Making sourdough isn't just a matter of intentional or unintentional contamination.

Are modern traditionally made farmhouse ales all a bit sour?

I could be wrong, but I thought that was the point.

 

[frithy]

Maybe eventually, but probably not if consumed fast enough.

That's what I'm thinking after reading this:
https://www.brewingnordic.com/farmhouse-ales/norwegian-farmhouse-ale-hornindal/
"Although this kveik is known to contain bacteria, I didn’t sense any sourness in the fresh ales. One several months old maltøl, which was brought just to educate me, tasted slightly tart, but not sour. It was not bad, though clearly inferior to the fresh ale."

So, I'm guessing before pasteurization beer was normally brewed hot and fast similar to modern kveik. The further you got from the pitch date, the more sour your drink. That makes me wonder if the pre-modern lagers were a generally tart beverage.

 

[frithy]

Shower thought:

• Why hasn't anyone created a submersible oxygen absorber? All you'd need is to put iron powder or some other oxygen reactive substance in a container that readily lets o2 pass but doesn't let the iron. It could be like the Guiness nitro balls. Million dollar invention.

 

[frithy]

Shower thought:

• Why doesn't anyone use mucilaginous plants to add body to a beer? If fermenting a style that demands body but using a highly attenuating yeast, couldn't you just add something from the mallow family to add mouthfeel? Why isn't this more common?

 

[VikeMan]

• Why doesn't anyone use mucilaginous plants to add body to a beer? If fermenting a style that demands body but using a highly attenuating yeast, couldn't you just add something from the mallow family to add mouthfeel? Why isn't this more common?

"More common" implies that someone has already done it at least once.

My guess as to why nobody does this is that it would also bring other compounds, with unknown and/or suspected/known undesirable consequences. Clorophyll anyone? Yum!

BTW, there are other well tested ingredients (e.g. oats, or pretty much any unmalted grain) that can be used to enhance mouthfeel, even in a highly attenuated beer. And, some very highly attenuative yeast strains, such as saison strains, produce significant amounts of glycosides, making a mouthfeel that belies the dryness of the beer.