# Compressed Air As Opposed To Co2



## chill73 (13/1/08)

I am just getting my keg system together and hope to be up and running in a month or sooner if possible. But I am in need of info on using compressed air instead of CO2. I have heard some talk from some old bar men who used to use comp air, they have said that it does the same job as CO2. If anyone has any thoughts or ideas on this it would be great to hear as it would help me decide which one to set up for. 

chill73


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## Thirsty Boy (13/1/08)

chill73 said:


> I am just getting my keg system together and hope to be up and running in a month or sooner if possible. But I am in need of info on using compressed air instead of CO2. I have heard some talk from some old bar men who used to use comp air, they have said that it does the same job as CO2. If anyone has any thoughts or ideas on this it would be great to hear as it would help me decide which one to set up for.
> 
> chill73




Pretty much a big old fashioned no I'm afraid.

Compressd air would push the beer out of the kegs in a pinch, but it it would also let oxygen at the beer. It would become stale and go flat very quickly indeed. You would taste the difference in the beer the next day and it would become undrinkably stale in only a few days after that. plus flat.

If you were going to drink the whole keg in one or two nights, you might get away with it, apart from that it needs to be C02. And at any rate, unless you have a food grade aircompressor, you would also be shooting an unhealthy amount of oil into your beer. It comes off the compressor's piston, into the air and would thence go into your beer.

The old barmen you heard talking were a unique subspecies of the breed... dodgey old barmen 

You'll have to pony up for the C02 I'm afraid

Thirsty


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## Adamt (13/1/08)

*sigh*

Oh dear.


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## sqyre (13/1/08)

Hi Chill73,
Firstly Welcome to the forum!.
Unfortunatly, Thirsty Boy is correct. Compressed air is Not an option.
The bubbles in your beer is CO2 and when using kegs the simplest way to put them there is through forced carbonation which is putting the beer under high pressure co2 to force the gas into the beer. You then use very low pressure co2 to push it out your tap which will uses bugger all co2 to do. Like TB said you could use compressed air to push it out once carbonated but unless your going to drink that whole keg in the next couple of hours i wouldn't advise it..

I have used Compressed air in an emergency, when my co2 ran out about 6pm on a saturday night but i only hooked it up to a keg that was a third full and i knew i would pretty much pollish it off that night.

In a nutshell, your going to have to use Co2...

Sqyre...


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## HKS (13/1/08)

I have never heard of a food grade air compressor either. I've never seen a food grade oil/water separator either.(I would buy 1 if I could find 1) I had to replace my oil/water separator recently as it split down the side after I bumped up the pressure to 65psi to pump up a bike tyre.

I decided I will also replace the coiled hose for longer straight hose. When I took the fittings out I noticed there was quite a bit of oil residue in the coiled air hose. This was with using an oil/water separator. That would be the last thing I would want in my beer.

I have heard that when the hand pumps are used its recommended that the keg gets polished off within 8 hours.

I would use a hand pump before I would use an air compressor and make sure that keg gets drunk very quickly.

If you are going kegging you need CO2. You are only a set of CO2 gauges and bottle away from kegging. Check the site sponsors for CO2 gauges and go down to your local BOC distributor and lease a gas bottle. I got prices locally recently and it was $119 per year for a VT (10kg, comes filled) and $117 for a D type (6kg, comes filled). Also the price difference to fill them is next to nothing.(like $24 for the D and $27 for the VT) Unless you are going through heaps and heaps of kegs a year you won't need to refill a VT. So it will cost you about $10 a month.

Cheers


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## domonsura (13/1/08)

Geez that's expensive for CO2............if I recall properly, I paid around $60 for my 10kg bottle...................


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## HKS (13/1/08)

domonsura said:


> Geez that's expensive for CO2............if I recall properly, I paid around $60 for my 10kg bottle...................



Wow that is cheap, 1/2 the price. I was quoted those prices from BOC Gas and Gear at Carrington (suburb of Newcastle, NSW)


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## kevnlis (13/1/08)

I paid $65 for 22 kilos of CO2 at the BOC here in Bundy. Plus $12 or so per month rental charge.


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## verock (13/1/08)

Don't use air, it'll ruin your work, not to mention the oil blowby. If you are on a budget try a "keg charger" available at www.grapeandgrainery.com for $21 (US) but it or something like it is probably available in you 'neighborhood'. You can naturally carbonate your beer with cornsugar, like a giant bottle; then use the keg charger to dispense it. One or two cartridges will empty a 5 gal keg. We use it on hunting/fishing/camping trips so we don't have to take the gauges, hoses, cylinder, etc.


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## Trent (13/1/08)

Domonsura
Is that $60 a yearly rental price, or an outright purchase price? I am *fairly* sure that the cylinder rental prices vary greatly from state to state. I have been led to believe that NSW is one of (if not the) most expensive states in Oz to rent from, at the happy price of around $120 or so a year.
I think that Victoria used to be the cheapest state to rent in, but I cannot recall the cost. Be interesting to see what people pay through the same supplier (eg BOC) in each state, I cant understand why the price varies, but have heard it has something to do with the amount of cylinders that go "missing". Hence, the more cylinders that go awol, the more they raise the rental prices to cover their losses. Maybe the Victorians are really honest? 
And, to keep it on topic, I wouldn't use compressed air either. Much smarter to fork out the $$ and get the right gear for the job, in my opinion.
All the best
Trent


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## chill73 (13/1/08)

Thanks for the feed back!

I think I shall check out my local fire extinguisher people, before renting from boc. And I also have a contact number for a guy in Adelaide who does refits on old steel extinguishers specifically for kegging.

Cheers

Chill73


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## SJW (17/3/08)

I just paid $48 for my VT c02 exchange in Newcastle.


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## masculator002 (17/3/08)

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.


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## masculator002 (17/3/08)

masculator002 said:


> 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.



oh and if you are using more than a vt bottle a year you are drinking way too much or you havent achieved a good seal in your kegs.

carbonate at 3.5 to 4 bar for 2 days at 0 degrees c, and pressurise for dispensing at about 10 psi or approx .5 to .75 bar


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## masculator002 (17/3/08)

chill73 said:


> Thanks for the feed back!
> 
> I think I shall check out my local fire extinguisher people, before renting from boc. And I also have a contact number for a guy in Adelaide who does refits on old steel extinguishers specifically for kegging.
> 
> ...



dont waste your time go to boc


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## KGB (17/3/08)

^^^ I disagree completely, BOC are damn expensive! ~$100 or more per year rental, + gas, + whatever deposit on the cylinder. If you go to the right places you can get a fire extinguisher setup for less than a years rental - and its yours forever!


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## mfdes (18/3/08)

KGB said:


> ^^^ I disagree completely, BOC are damn expensive! ~$100 or more per year rental, + gas, + whatever deposit on the cylinder. If you go to the right places you can get a fire extinguisher setup for less than a years rental - and its yours forever!



Yeah, and then you have to have it hydrostatically tested regularly before anyone will fill it up for you. legally at least.

MFS


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## ausdb (18/3/08)

HKS said:


> If you are going kegging you need CO2. You are only a set of CO2 gauges and bottle away from kegging. Check the site sponsors for CO2 gauges and go down to your local BOC distributor and lease a gas bottle. I got prices locally recently and it was $119 per year for a VT (10kg, comes filled) and $117 for a D type (6kg, comes filled). Also the price difference to fill them is next to nothing.(like $24 for the D and $27 for the VT) Unless you are going through heaps and heaps of kegs a year you won't need to refill a VT. So it will cost you about $10 a month.


I think they are quoting you for the rental only, BOC always charge for cylinder rental plus the fill when you start off


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## devo (18/3/08)

chill73 said:


> I am just getting my keg system together and hope to be up and running in a month or sooner if possible. But I am in need of info on using compressed air instead of CO2. I have heard some talk from some old bar men who used to use comp air, they have said that it does the same job as CO2. If anyone has any thoughts or ideas on this it would be great to hear as it would help me decide which one to set up for.
> 
> chill73



Surely this gotsta be a troll?!


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## pint of lager (18/3/08)

Double check your figures. Out here in rural NSW. it is about $120 a year rental and $45 a refill on a VT 10kg BOC cylinder. A cylinder lasts about 18 months, so that works out about $13 a month.

Owning a cylinder is not feasible out this way. No-one actually refills them, they are just swap out. The BOC or Air Liquide empties go back to the big smoke to be refilled.

If you do go down the buy your own cylinder, make sure that the refilling station is not an hour's drive away and only open 8am-4pm 5 days a week. Also calculate in regular cylinder retests. Many people on the forum are happy fire extinguisher users, but it is not feasible for everyone.


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## floppinab (18/3/08)

devo said:


> 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.


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## devo (18/3/08)

floppinab said:


> 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


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## Rabbitz (18/3/08)

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)


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## devo (18/3/08)

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


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## SJW (18/3/08)

Use C02, NOT AIR!


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## chovain (18/3/08)

Rabbitz said:


> 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.


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## masculator002 (18/3/08)

masculator002 said:


> 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.


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## masculator002 (18/3/08)

Rabbitz said:


> 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.
> 
> ...



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.


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## benno1973 (18/3/08)

Rabbitz said:


> 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


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## SJW (19/3/08)

> 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


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## shonky (19/3/08)

> 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


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## chovain (19/3/08)

SJW said:


> 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).


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## PostModern (19/3/08)

shonky said:


> 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.


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## Rabbitz (19/3/08)

Mark Chovain said:


> 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


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## Rabbitz (19/3/08)

Kaiser Soze said:


> 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


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## chovain (19/3/08)

PostModern said:


> 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.


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## shonky (19/3/08)

> 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


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## newguy (19/3/08)

Rabbitz said:


> 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.


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## PostModern (19/3/08)

shonky said:


> . 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.


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## Rabbitz (19/3/08)

Mark Chovain said:


> 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".


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## Thirsty Boy (19/3/08)

shonky said:


> . . . . . I think 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



Unless they are terribly unhealthy and simply lack the internal resources, or the level of alcohol is too high for them, yeast will reproduce to sufficient levels to ferment available sugars. Regardless of the level of 02. They probably wouldn't have enough resources to go all the way through a batch from scratch without extra 02... but enough for bottle conditioning? Yes they can and do reproduce. I could quote theory, but I don't have too, I have a practical example.

I sometimes filter into bottles and then prime the bottles. The filter removes almost all the yeast, but a very few (probably newly budded and therefore small enough to slip through the filter pores) cells do get through. These reproduce sufficiently to carbonate the beer and leave a very minimal layer of sediment in the bottle. I know its not just the yeast that made it through the filter, because when I filter into a keg, force carbonate and CP fill bottles... there is no visible sediment at all.

Perhaps I get a little 02 into solution during the bottling phase... but certainly not a lot, I am pretty careful about it and I purge bottles with C02 etc. Definitely no more than the average brewer would get in transferring into a keg to be primed for carbonation. So you would certainly get an amount of sediment in a naturally primed keg, presumably at proportionally the same levels you would get in a bottle conditioned beer. Fine if the keg is going to stay undisturbed in your keggerator and can settle for a long time, couple of pints on the garden and it will run clear ... not so great if you need to move it about the place or take it to a party or something.

Probably worth maybe a teaspoon of sugar in even filtered & force carbed kegs... just so that any yeast present try to grow and scavenge up any O2 that would otherwise go towards staling the beer.


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## masculator002 (19/3/08)

SJW said:


> 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



how do you think you end up with yeast in the bottom of your bottles after a secondary fermentation?????


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## Darren (19/3/08)

Not sure if this is mentioned or relevent to this discussion but, alcohol production is entirely reliant on anaerobic conditions (ie. no oxygen). 

As for the cask ales, I agree with Post Modern, they are not force carbonating the cask so the only oxidation that would occur is at the surface.

Pumping any amount of O2 into beer is bad if you wish to hang on to it for a while. Oxygen causes oxidation (similar to rust of metal) once it starts it never stops.

cheers

Darren


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## MHB (19/3/08)

> masculator002 Posted Today, 07:21 PM
> QUOTE (SJW @ Mar 19 2008, 10:23 AM)
> 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
> 
> ...



Thats yeast that was in suspension settling out; when beer is cask clear (i.e. appears clear to the naked eye) you still have 5-10 thousand yeast cell/millilitre of beer.



> Thirsty Boy Posted Today, 01:19 PM
> sometimes filter into bottles and then prime the bottles. The filter removes almost all the yeast, but a very few (probably newly budded and therefore small enough to slip through the filter pores) cells do get through. These reproduce sufficiently to carbonate the beer and leave a very minimal layer of sediment in the bottle. I know its not just the yeast that made it through the filter, because when I filter into a keg, force carbonate and CP fill bottles... there is no visible sediment at all.



I think in this case the yeast has settled out in the keg, and you arent transferring it to the bottles.
Good enough observation but not a causal argument.

MHB


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## SJW (19/3/08)

> 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.


Well have u primed a keg with sugar? and what was the results?




> Thats yeast that was in suspension settling out; when beer is cask clear (i.e. appears clear to the naked eye) you still have 5-10 thousand yeast cell/millilitre of beer.


Thanks Mark. We was only talking about this the other day.

Steve


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## kook (19/3/08)

masculator002 said:


> 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've done this with english beers (highly flocculative yeast) and you only have a cloudy pour for the first pint or so. After that the remaining yeast clings to the round base of the keg, and won't shift till you pour the final pint (or stir up the keg).

I use a fire extinguisher without any issues. There is no "fire retardant" in a CO2 extinguisher. So long as you buy a new one and it is properly cleaned, there is no issue whatsoever. It's a hell of a lot cheaper, and the CO2 is supposedly filled from the same bulk tank as the food grade CO2.


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## Thirsty Boy (20/3/08)

MHB said:


> Thats yeast that was in suspension settling out; when beer is cask clear (i.e. appears clear to the naked eye) you still have 5-10 thousand yeast cell/millilitre of beer.
> 
> 
> 
> ...


 

well, except for the fact that its usually all happening about 5 minutes after I've spent half an hour shaking the bejeezus out of the keg. No, I'm talking about diamond bright, just been through a 1 micron absolute filter, very very clear beer. You can leave that keg standing there for a month and there still isn't sediment on the bottom of it, same for CP filled bottles from the freshly shaken keg. BUT - put beer through the same filter into a bottle and add some priming sugar, and there is a very light, but present layer of yeast. Which either appeared by magic... or reproduced from the minuscule quantities that made it through the filter.

I don't believe in magic.. but I do believe that _was_ a causal argument. Or near enough to one for government work at any rate 

TB


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## MHB (20/3/08)

TB

Rather than shoot from the lip I went and did a bit of digging, from what I can find looks like we are both partly right and wrong.

Yes some yeasts can reproduce anaerobically, but this summed up the situation best:-



> Brewing yeasts do not develop respiratory competence under the conditions encountered in fermentation. Thus, in the aerobic phase of fermentation, respiratory pathways are repressed because of the presence of sugars. In late fermentation when the sugars have disappeared and their repressing effects are relieved, anaerobiosis prevents the induction of the respiratory enzymes.
> 
> The majority of yeasts require oxygen for growth. In a study of type species from 75 genera, it was noted that only 23% could grow under anaerobic conditions on a complex medium supplemented with ergosterol and a source of unsaturated fatty acids (Visser et al., 1990). Of these, S. cerevisiae was exceptional in that it was capable of rapid growth at low oxygen tension. Nevertheless, none of these yeasts, including S. cerevisiae, can grow under totally anaerobic conditions unless the medium is supplemented with a source of unsaturated fatty acids and sterols (Andreason and Stier, 1953 ab). These essential metabolites can be assimilated from the medium or synthesized de novo from carbohydrates. Synthesis requires the presence of molecular oxygen. Both of these are present in wort at the start of fermentation.
> 
> ...



If you filter to 1um obviously as you observed you are removing all the mature yeast. I suspect that when you force carbonate, pressure prevents the yeast from further development; so the cells remain small and invisible to the naked eye.

When you bottle condition the low initial pressure and the presence of food (priming sugar) allows the yeast to mature.

My best guess is that there is the same population but in one case the yeast is just bigger.

This has always been one of those questions that bugs me - if you have further information I would like to look at it, please e-mail (address in footer).

MHB


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## Darren (20/3/08)

TB,

Seems to me you are once again being pedantic about a miniscule point but have missed the obvious. You DID add oxygen at bottling. Maybe you think it was "hardly any" but the fact remains your bottle contained ~21% oxygen before you added the beer. No matter how much you purged your bottle oxygen would have been included, let alone how much oxygen was dissolved in your priming sugar.

cheers

darren


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## oldbugman (20/3/08)

Can I hook my kegs up to the tail pipe of my car and let the carbon emission fairies do the rest?


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## Whistlingjack (20/3/08)

Darren said:


> TB,
> 
> Seems to me you are once again being pedantic about a miniscule point but have missed the obvious. You DID add oxygen at bottling. Maybe you think it was "hardly any" but the fact remains your bottle contained ~21% oxygen before you added the beer. No matter how much you purged your bottle oxygen would have been included, let alone how much oxygen was dissolved in your priming sugar.
> 
> ...



The increase in temperature of the beer, even by a few tenths of a degree, during bottling will force CO2 out of solution. Any oxygen that is in the bottle will be driven to the top. Unless the bottle is disturbed during conditioning, it will remain there.

WJ


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## Darren (20/3/08)

WJ,

Would be hard not to disturb a bottle at the HB level.

What about the priming sugar??

cheers

Darren


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## milpod (20/3/08)

Unfortunately,when it comes to co2, they have us by the short and curleys.

Looked into every option,including 22kg lease and refill gear.

After a few hours reading,I decided I'd rather pay.My life is far more important then a few $.

Swap and go for co2 would be sweet,evetually it will happen.

Ok a population of 25 million,it wont.


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## Whistlingjack (20/3/08)

Darren said:


> WJ,
> 
> Would be hard not to disturb a bottle at the HB level.
> 
> ...



I'm talking about the time after the bottle is filled. I added the sugar to the bottle, then the beer, then capped.

I inverted the bottle afew times then stored it upright. As O2 is the lightest gas, it will rise and occupy the top section of the headspace. Leave the bottle alone and there will be no mixing of gases.

WJ


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## sathid (20/3/08)

I think diffusion would cause you some problems there mate. 

You are saying that after the bottle has been capped, that you will have a layer of CO2 under a layer of O2 right?

Well the concentration difference in the two layers will mean that well before you open that bottle, you will have a pretty much heterogeneous mixture of O2 and CO2, and no layers.


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## Stuster (20/3/08)

Whistlingjack said:


> As O2 is the lightest gas, it will rise and occupy the top section of the headspace.



Not how it works, WJ. In a bottle headspace (or any space come to that) you'll get an even distribution of all gases occurring over time. Gases mix, despite any differences in their atomic mass. That's also true for the old chestnut of CO2 sitting blanket-like on top of your fermenting beer. <_<


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## SJW (20/3/08)

> I think diffusion would cause you some problems there mate.
> 
> You are saying that after the bottle has been capped, that you will have a layer of CO2 under a layer of O2 right?
> 
> Well the concentration difference in the two layers will mean that well before you open that bottle, you will have a pretty much heterogeneous mixture of O2 and CO2, and no layers.



Please! :angry:


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## sathid (20/3/08)

please what?


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## Thirsty Boy (21/3/08)

Darren said:


> TB,
> 
> Seems to me you are once again being pedantic about a miniscule point but have missed the obvious. You DID add oxygen at bottling. Maybe you think it was "hardly any" but the fact remains your bottle contained ~21% oxygen before you added the beer. No matter how much you purged your bottle oxygen would have been included, let alone how much oxygen was dissolved in your priming sugar.
> 
> ...



Of course I get added 02 at bottling. Not much, because the bottles are carefully purged with C02 and the sugar is dissolved in water and boiled, thusly driving out the majority of the oxygen... but indeed, some 02 would be introduced.

Of course if you read my post carefully you would have noticed that I qualified the whole point by comparing it to the amount of 02 that would be taken up in process of transferring to a keg and said rather than that I get no 02 pick-up, but that its most likely to be less than the amount most homebrewers pick up in transferring to a keg. So the levels of oxygen in the containers I was observing would be less than or equal to a keg and inferences about yeast behavior in a low oxygen environment would be comparable in the two situations.

Strangely enough having worked in the brewing industry for 17 years... I actually do know some of the mechanics of controlling 02 pick-up in the brewing process and took them into account before I posted. But thats beside the point, I'm sure you'll notice something else obvious that I missed.

MHB - nice stuff there. I suspect once again that you are fairly close to the mark. The immature cells reaching maturity plus a limited amount of reproduction - both aerobically from the inevitable amount of o2 ingress that Darren pointed out and some limited anerobic growth from residual sterol levels within the cells and fatty acids etc in the beer. All of them adding up to the fine layer of yeast I observed.

Thanks Mark, I learned something from your post.

Thirsty


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## SJW (21/3/08)

> please what?


Please stop talking shit


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## Whistlingjack (21/3/08)

Stuster said:


> Not how it works, WJ. In a bottle headspace (or any space come to that) you'll get an even distribution of all gases occurring over time. Gases mix, despite any differences in their atomic mass. That's also true for the old chestnut of CO2 sitting blanket-like on top of your fermenting beer. <_<



I take your point.

My understanding of the partial pressures exerted by gaseous substances tells me that each one, over time, will find its own space.

I'm not a physics expert, so I'm open to correction.

WJ


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## devo (21/3/08)

OldBugman said:


> Can I hook my kegs up to the tail pipe of my car and let the carbon emission fairies do the rest?




HAHAHAHA orsum :lol:


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## sathid (22/3/08)

SJW said:


> Please stop talking shit


Erm, I didn't think I was. Please elaborate. :unsure:


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## Thirsty Boy (22/3/08)

Whistlingjack said:


> I take your point.
> 
> My understanding of the partial pressures exerted by gaseous substances tells me that each one, over time, will find its own space.
> 
> ...



Brownian motion stuffs it all up


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## mesa (22/3/08)

Well moving fairly far afield from the original topic I thought I might comment a few points to this whole diffusion of gases discussion.

CO2 and air will mix in a process called Brownian motion (technically I think Brownian motion refers to the molecules eratic course if you look at it closely and difffusion is the mixing process, but thats a bit pedantic). However it takes a little while (on the order of minutes) depending how how warm the gases are. I think most people have seen dry ice melt and the layer of vapour formed, but not thought about how long that layer will hang around.

Of course light gases will separate from heavy gases (it happens all the time in the atmosphere as helium escapes the earth and wanders off into space) but to cause CO2 and O2 to separate you've either got to have them very cold so that Brownian motion doesn't mix them back up again faster than they settle, or in a very strong gravity field (i.e. a Centrifuge). (Actually I'm not sure it would work even then because then the molecules no longer act like a gas and start to turn into a liquid which is how we usually separate them, by condensing them into a liquid out of the air)

I also wanted to comment about sathids speculation that CO2 doesn't form a protective blanket on your fermenting beer. I'm not sure if you were talking about a fermenter with the lid off (in which case you would be correct) but a fermenter with the lid on with either an airlock of just a small hole like the clingwrap method will certainly slow down the diffusion process to the point where it is insignificant compared to the amount of new CO2 created. Just remember to get it sealed up once its finished fermenting. Likewise I'd have to say that purging your bottles with CO2 works inspite of diffusion processes because the time between purge and fill and cap is so short (not that I do this, never really had a problem with the flavour of any of my bottles so I won't spend CO2 on it ;-)

--
Mesa.


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## sathid (23/3/08)

I wasn't saying there would be no blanket of co2 in a fermenter, I was saying that if you got some oxygen in a sealed bottle, you would not have a layer of air, over a layer of CO2.


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## mesa (23/3/08)

Sorry for the misunderstanding sathid, your absolutly right about the air in the bottle scenario.


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## sathid (25/3/08)

No worries 

I'm still waiting to find out what SJW meant when he told me to stop talking shit


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