Compressed Air As Opposed To Co2

[floppinab]

Surely this gotsta be a troll?!

Not a troll devo, a legitimate question. I've heard similar stories for this to have happened "back in the day", if compressed air was easier (cheaper??) to get hold of, given pubs are turning over beer pretty quickly, and they were probably tapping and dispensing one at a time rather than having gas manifolds and multiple lines. As others have said in this thread if your beer has been carbed with CO2 then there is nothing wrong with using compressed air to dispense if the keg is emptied within a handful of hours. Wouldn't want to be having the first brew or two from that pub the next day though :icon_vomit: .

However most home beer setups will not turn over kegs that quickly, plus most keggers want to force carb which you wouldn't want to do with compressed air.

 

[devo]

Not a troll devo, a legitimate question. I've heard similar stories for this to have happened "back in the day", if compressed air was easier (cheaper??) to get hold of, given pubs are turning over beer pretty quickly, and they were probably tapping and dispensing one at a time rather than having gas manifolds and multiple lines. As others have said in this thread if your beer has been carbed with CO2 then there is nothing wrong with using compressed air to dispense if the keg is emptied within a handful of hours. Wouldn't want to be having the first brew or two from that pub the next day though :icon_vomit: .

However most home beer setups will not turn over kegs that quickly, plus most keggers want to force carb which you wouldn't want to do with compressed air.

eew nasty

 

[Rabbitz]

So I am confused. There are a few references to the beer being flat if Air is used instead of CO2. This doesn't seem possible.

Before we get all excited, firstly I am not saying to use air as it is clearly inappropriate, having O2 in it.

So on to the "flat beer". By flat beer I assume this to mean that it wont have bubbles in it.
If one thinks back to basic gas laws, in fact Dalton's and Henry's laws, then what I am suggesting may become clear:

Dalton - The partial pressure of a gas in a mixture is equal to the pressure it would exert if it occupied the same volume alone at the same temperature. In other words the percentage of the gas in the mix will equal the percentage of the total pressure it will exert.

Henry - The concentration of a gas in a solution is directly proportional to the partial pressure of that gas above the solution.

So the amount of bubbles (or carbonation in the case of CO2) and therefore the flatness of a beer relates directly to the amount of gas dissolved in the beer while under pressure. Once the the pressure is released (the beer is poured) then the gas comes out of solution and forms bubbles.

So if Dalton's and Henry's Laws hold true then regardless of the pressurising gas the solution will absorb that gas (in proportion to its constituent parts) to a point of equilibrium which is temperature and pressure dependent. Clearly temperature can be discounted as in a fair test both samples would be the same, same for pressure. (Time also plays a part as it takes time to reach equilibrium)

So I believe that the beer would not be "flat" it would in fact out gas once pressure is released.

The bubbles may not be of an ideal size, nor would the effect on the beer necessarily be the same but it wouldn't be flat.

Interestingly, I have done this experiment with both water and rendered chicken fat, after a couple of hours at 5 ATA with a rapid decompression both formed large visible bubbles...

Rabz

(edited to fix grammar)

 

[devo]

bubbles or no bubble, it would oxidised and basically taste like shit which is want you don't want.

 

[SJW]

Use C02, NOT AIR!

 

[chovain]

So I am confused. There are a few references to the beer being flat if Air is used instead of CO2. This doesn't seem possible.

It will most certainly lose carbonation. It won't go completely flat, but it will come out with a lot less bubbles than you intended. Is you pump in air, the partial pressure of CO2 will drop. The air displaces beer, increasing the head space. You now have the same amount of CO2 in a larger volume.

The lower partial pressure will cause CO2 to come out of solution. By my estimates, a keg with about 5L left will be at about half the levels of dissolved CO2. A beer at 1.25 volumes CO2 might as well be flat. :icon_vomit:

Again, if you drink the beer fast enough, it won't have time to equalise, but that's rarely the case for home brewers.

 

[masculator002]

compressed air will do a good job....... of sending your beer to the toiletpay the cash and get a co2 bottle. They are easy to get and not that expensive. I paid about 35 bucks for 3 months rental and I think it was like 42 bucks for the gas. It is cheaper to get it with 12 months rental. If you need a reg I have a spare one I am willing to part with. It is a cig one and is designed for food grade c02 dispensing. DO NOT try to use compressed air unless you want to drink a keg in one sitting and are willing to put up with it tasting like shit.

I have checked the reciept I got from boc and the prices That I have quoted are correct if your distributor is charging more than this I will post the contact number I have for BOC and You can argue it with the head honcho. as also stated If you go the fire extinguisher way it must be certified every five years I believe, you must also find someone who will fill it and last but not least i would say that the chemicals in the retardant used in fire extinguishers would not be too good for your health.

 

[masculator002]

So I am confused. There are a few references to the beer being flat if Air is used instead of CO2. This doesn't seem possible.

Before we get all excited, firstly I am not saying to use air as it is clearly inappropriate, having O2 in it.

So on to the "flat beer". By flat beer I assume this to mean that it wont have bubbles in it.
If one thinks back to basic gas laws, in fact Dalton's and Henry's laws, then what I am suggesting may become clear:

Dalton - The partial pressure of a gas in a mixture is equal to the pressure it would exert if it occupied the same volume alone at the same temperature. In other words the percentage of the gas in the mix will equal the percentage of the total pressure it will exert.

Henry - The concentration of a gas in a solution is directly proportional to the partial pressure of that gas above the solution.

So the amount of bubbles (or carbonation in the case of CO2) and therefore the flatness of a beer relates directly to the amount of gas dissolved in the beer while under pressure. Once the the pressure is released (the beer is poured) then the gas comes out of solution and forms bubbles.

So if Dalton's and Henry's Laws hold true then regardless of the pressurising gas the solution will absorb that gas (in proportion to its constituent parts) to a point of equilibrium which is temperature and pressure dependent. Clearly temperature can be discounted as in a fair test both samples would be the same, same for pressure. (Time also plays a part as it takes time to reach equilibrium)

So I believe that the beer would not be "flat" it would in fact out gas once pressure is released.

The bubbles may not be of an ideal size, nor would the effect on the beer necessarily be the same but it wouldn't be flat.

Interestingly, I have done this experiment with both water and rendered chicken fat, after a couple of hours at 5 ATA with a rapid decompression both formed large visible bubbles...

Rabz

(edited to fix grammar)

Unless you are performing a secondary fermentation in your keg It will never carbonate at all which leads to another problem the huge amount of sediment you will get if you are priming a keg like a bottle. save yourself a lot of heartache time and money which would be wasted by cahsing a pipe dream and get what you know is right from the word go, after all you will end up doing it anyway and at the end of the day you know it is safe for use with food stuffs and beverages.

 

[benno1973]

Interestingly, I have done this experiment with both water and rendered chicken fat, after a couple of hours at 5 ATA with a rapid decompression both formed large visible bubbles...

Yeh, but the rendered chicken fat probably didn't taste as good the next day, eh? Which is why I always carb my rendered chicken fat with CO2, otherwise it just tastes like crap

 

[SJW]

Unless you are performing a secondary fermentation in your keg It will never carbonate at all which leads to another problem the huge amount of sediment you will get if you are priming a keg like a bottle. save yourself a lot of heartache time and money which would be wasted by cahsing a pipe dream and get what you know is right from the word go, after all you will end up doing it anyway and at the end of the day you know it is safe for use with food stuffs and beverages.

I can't see how you would get any more yeast in the keg by priming the keg. There should be little o2 in the beer for yeast reproduction

 

[shonky]

Yeh, but the rendered chicken fat probably didn't taste as good the next day, eh? Which is why I always carb my rendered chicken fat with CO2, otherwise it just tastes like crap

- Classic

I want to make it clear up front that I am NOT advocating either gassing or dispensing with air, but I just feel like stiring this particular hornets nest a bit more.

Many posters on this forum and in many brewing (home and commercial) textbooks talk about a "blanket of CO2" protecting beer (I believe this to be true only during primary fermentation when loads of CO2 is being generated). I know there has been some debate about this and the extent to which difusion my cause the two gases to mix, particularly if no co2 is being generated (see here). But assuming there is some protection AND if the beer has been force carbonated with CO2 pumping the beer out with air may be relatively safe for a longer period than a few hours.

Another thing to bear in mind in this whole debate is that with Real Ales it is mandated by CAMRA that the head space in the emptying barrel be filled with atmospheric air. There aren't many pubs (English) which empty a barrel in a 'few hours'. From memory 5 or 6 days seems to be a good rule of thumb when working with english hand pumped beers (also from memory there was talk that some of the yeast strains used in real ales today allow for much longer) - perhaps someone with cellar expereince might be able to comment with more authority (dellboy?). With English real ales at least IIRC, the mixing of air in the barrel is considered to be an important part of generating the flavour profile of these beers.

Cheers

 

[chovain]

I can't see how you would get any more yeast in the keg by priming the keg. There should be little o2 in the beer for yeast reproduction

I once thought this too, but yeast can apparently reproduce anaerobically. I understand it extracts the oxygen it needs from other molecules using energy stored from conventional fermentation.

Edit: Can any of the bio people confirm this? I can only find weak references for this: Undergrad assignments that state it as an assumption, and papers that discuss anaerobic reproduction of fungi (but not specifically brewers' yeast).

 

[PostModern]

Another thing to bear in mind in this whole debate is that with Real Ales it is mandated by CAMRA that the head space in the emptying barrel be filled with atmospheric air.

Atmospheric air at amospheric pressure. Ram it in there under pressure and more of it will end up in solution, same as CO2.

 

[Rabbitz]

It will most certainly lose carbonation. It won't go completely flat, but it will come out with a lot less bubbles than you intended. Is you pump in air, the partial pressure of CO2 will drop. The air displaces beer, increasing the head space. You now have the same amount of CO2 in a larger volume.

The lower partial pressure will cause CO2 to come out of solution. By my estimates, a keg with about 5L left will be at about half the levels of dissolved CO2. A beer at 1.25 volumes CO2 might as well be flat. :icon_vomit:

Again, if you drink the beer fast enough, it won't have time to equalise, but that's rarely the case for home brewers.

I am not entirely convinced, and let me say I don't believe for second air should be used.

As pressure is increased in the keg, and the CO2 PP drops it will effectively be replaced by N2 and O2. These will also go into solution. If the pressure does not drop then no CO2 comes out of solution as the pressure of CO2 (absolute) has not dropped, merely its relative percentage. So as we dispense and the headspace increases the CO2 in solution will become relatively less, but the amount of O2 and N2 in solution will have (relatively) increased. As we dispense more then the bubbles appearing in the beer will change in mix (and probably effect) but they will still be there.

Now, are 02 and N2 suitable for "carbonation"? I really don't know, but isn't Guinness part N2 dispensed? Given that air is about 79% N2 then it might not be all bad. However the O2 will clearly cause some issues and frankly this screws the whole theory!!!

What sort of pressures are we talking about?

Rabz

 

[Rabbitz]

Yeh, but the rendered chicken fat probably didn't taste as good the next day, eh? Which is why I always carb my rendered chicken fat with CO2, otherwise it just tastes like crap

I have to admit I wasn't game to taste it (even on the first day prior to "carbonation").

For those who are wondering why I would do this anyway, it was a demonstration of gas absorption and release as part of a diving decompression lecture. Essentially I gave the chicken fat "the bends" to show that bubbles do form with fast decompression.

And also I had the tools and ingredients so why not?

Rabz

 

[chovain]

Atmospheric air at amospheric pressure. Ram it in there under pressure and more of it will end up in solution, same as CO2.

I don't think anyone is really claiming that Real Ale is anything but flat, are they? You're never going to ram air in hard enough to carbonate a regular beer to acceptable levels. Here's why:

Although the constants from Henry's law for each of the constituents of atmospheric air is absolutely tiny compared to that of CO2.

According to Wikipedia and this analysis:
Nitrogen, making up 78% of the atmosphere, has a solubility of less than 0.005% of CO2's.
Oxygen makes up 21% with soluability less than 3.8% of CO2's.
Argon comes in at 1%, with soluability less than 4.2% of CO2's.
We can ignore the rest, which are water vapour, and about 0.002% other stuff.

Dalton says we can just do a weighted average of those (we're adding the partial pressures), so atmospheric air has a soluability of about a hundredth that of CO2 (0.8%).

We normally carb beers at about 70-75kPa (That's ~175kPa absolute, as our pressures gauges are relative to atmospheric pressure). To get the equivilent carbonation from air, you're going to need about 110 times that pressure: 19MPa. Good luck getting an air compressor *that* big.

 

[shonky]

Atmospheric air at amospheric pressure. Ram it in there under pressure and more of it will end up in solution, same as CO2.

. Not sure I see the difference between pouring a pint of real ale (with hand pump not directly out of the barrel) and pumping just enough air into the headspace to pour a kegged beer?

When pouring a real ale the air will be entering the barrel at more than atmospheric pressue otherwise there will be a vacuum created (assuming you are pumping from a cellar and not by gravity.

I once thought this too, but yeast can apparently reproduce anaerobically. I understand it extracts the oxygen it needs from other molecules using energy stored from conventional fermentation

I thjink I agree with SJW here. My understanding is that it is the presence of sugars AND oxygen that will switch the yeast back to reproducing mode. The majority of oxygen will have been metabolised by the yeast within the first few hours after pitching for sterol synthesis. The most important sterol is ergosterol (can be over 90% of total sterol) and to quote Brewing Science & Technology, Brewers Yeast "the final reaction that produces ergosterol requires molecular oxygen". And from Briggs - Brewing Science and Practice - "In the yeast crop obtained at the end of fermentation, sterol and unsaturated fatty acid levels are reduced to growth-limiting concentrations, hence, the need for oxygenation of wort in the next fermentation". I think the important point here is not that more yeast is being created in the keg but that fermentation is kicked off again by the yeast still present in the beer. A final quote from Handbook of Brewing - Chpt 10 which may answer your question Mark "When a brewer's yesat is grown anaerobically, it accumulates sterols and unsaturated lipids within the cell in excess of the yeast's minimum requirements and the lipids can be "diluted" to a degree by subsequent growth without negative effects. As a result, cells preparad aerobically can grow to some extent anaerobically. However, if yeast is harvested at the end of fermentation and used to inocculate a second batch of wort, then oxygen is required because the new inoculum contains no reserves of the necessary lipids"

RDWHB

 

[newguy]

As pressure is increased in the keg, and the CO2 PP drops it will effectively be replaced by N2 and O2. These will also go into solution. If the pressure does not drop then no CO2 comes out of solution as the pressure of CO2 (absolute) has not dropped, merely its relative percentage. So as we dispense and the headspace increases the CO2 in solution will become relatively less, but the amount of O2 and N2 in solution will have (relatively) increased. As we dispense more then the bubbles appearing in the beer will change in mix (and probably effect) but they will still be there.

Nope. The pressure of what's "above" the beer doesn't matter to the CO2 dissolved inside the beer; what's important is that it (ie air) is CO2 "poor" compared to the pure CO2 in the beer. The CO2 molecules only "see" other CO2 molecules. Therefore 40psi of air to carbonated beer is the same, from the CO2's point of view, as the keg/bottle being open to the air. The net result is that the beer will go flat - CO2 flat. The other gases in air don't dissolve in water worth a damn, so the net effect is that the beer will go flat.

Now, are 02 and N2 suitable for "carbonation"? I really don't know, but isn't Guinness part N2 dispensed? Given that air is about 79% N2 then it might not be all bad. However the O2 will clearly cause some issues and frankly this screws the whole theory!!!

What sort of pressures are we talking about?

Well, for the nitrogen "widget" cans like Guiness, Boddington's, etc, the brewer does some pretty weird things. And these things involve very high pressures in order to get the nitrogen to dissolve into the beer. On the canning line, a hollow plastic ball or cylinder is dropped into the can. This is the widget. The widget has one tiny hole in it, and believe it or not, there have been many scientific studies whose sole aim were to determine the optimum diameter of that hole. From memory, I believe that the hole in modern widgets is 0.6mm in diameter.

Once the widget has been dropped into the can, and it has been filled with beer, a tiny shot of liquid nitrogen is squirted into the beer just before the top of the can is crimped on. Once the nitrogen boils off, it has nowhere to go but into solution. Over time, some beer is forced into the widget as well. Once the can is opened, the pressure inside the can is relieved. This means that the pressure holding the beer inside the widget is also relieved, and it jets out. This jet provides turbulence, which in turn provides nucleation sites for the dissolved nitrogen to come out of solution. This forms the thick, creamy head found on these types of beers. If you suck some normal beer into a syringe and then ram down on the plunger, you'll see the same effect. The difference is in the lifetime of the head, which will be much longer with dissolved nitrogen, which equates to much smaller bubbles.

I know people who have (and still do) dispense with "beer gas", a 60/40 mix of nitrogen and CO2. Unless you dispense the beer with a stout faucet, the net result is disappointingly flat beer, even with ridiculously high tank pressures.

 

[PostModern]

. Not sure I see the difference between pouring a pint of real ale (with hand pump not directly out of the barrel) and pumping just enough air into the headspace to pour a kegged beer?

When pouring a real ale the air will be entering the barrel at more than atmospheric pressue otherwise there will be a vacuum created (assuming you are pumping from a cellar and not by gravity.

The OP was talking about a compressor putting several PSI of air into the beer. Handpumps pull beer from the cask and air is allowed into the casks to replace the beer. You can't force carbonate a keg with atmos pressure CO2, so I imagine you won't be able to force "air" a beer with atmos pressure air. The only oxidisation going on at atmospheric pressure is the interaction bettween the beer on the surface with the O2 in the air. With the air under pressure, you're "forcing" air into the beer, potentially oxidising it more quickly. I think there's a difference, but I'm no physicist.

 

[Rabbitz]

We normally carb beers at about 70-75kPa (That's ~175kPa absolute, as our pressures gauges are relative to atmospheric pressure). To get the equivilent carbonation from air, you're going to need about 110 times that pressure: 19MPa. Good luck getting an air compressor *that* big.

Ok I get it now, being as I am not an expert on soluability (or any physics for that matter) I concede the argument.

However I will not concede that getting a compressor of 19MPa is difficult...
Go into any dive store and ask them. 19MPa is about 2700 psi which is less than a standard oud fashioned air fill for SCUBA diving.... 300Bar or 30MPa(ish) is becoming the "standard".