Question about carbonation in a half empty bottle

[alpo]

I did the 1-2-3 method with AHS's Blue Moon clone kit (partial mash) and bottle with 32 oz swingtops.

The trouble is, with that size bottle, I was left with about 12-14 ounces left in the last bottle. I figured what the hell, I blasted some argon into the bottle (from my wine rack) to get rid of the oxygen and capped it anyway.

Fast forward to last Saturday. I still have one week left, but I figured what the hell. A half bottle isn't really going to condition correctly anyway, so I stuck it in the freezer for 45 minutes and cracked it open. First off, the air blasted out of it like the muzzle fire from a .50 caliber sniper rifle. Seriously, I saw a flash of air shoot out like 4 feet in every direction and it made me flinch.

Anyway, the beer tasted very good. I was pleasantly surprised. However, it was significantly undercarbonated.

I just wanted to make sure... do you think the undercarbonation is a result of the beer being 1 week premature and the (huge) bottle being half empty? I figure all the empty space leaves a lot of room for the CO2 to expand into, rather than staying inside the beer.

I am not worried, per se, but I wanted some reassurance. I am going to be patient and wait until Saturday before I open a real bottle, so I guess I will find out for sure on that day, regardless.

 

[Jaha35]

Carbonation all has to do with pressure. If you have too much empty space in the bottle then little CO2 will be pushed into your beer because it has too much space to occupy elsewhere.

Basically what you got was a big blast of CO2 that was in the top of the bottle. All bottles pop like that but because there is such a small area it is hardly noticeable.

I am new to homebrewing but the science is pretty normal. I am not sure if you could get carbonation in a half bottle. I am sure you could get some but remember you have less yeast/priming sugar and a lot more space to fill with CO2 before you get the right about of pressure to carb it.

I have read in a book somewhere that capping half full bottles of beer can be dangerous. I guess thats why.

 

[dontman]

A couple things. The undercarbonation is from the CO2 not getting a chance to dissolve into solution once chilled. It needed more time in the fridge.

Second. You should never half fill a glass bottle because it is the surest way to create a bottle bomb. Read about it in Papazian. You were lucky that it didn't explode as you handled it. Especially one of those bottles. It's counterintuitive but the less full the bottle the more pressure the carbing beer will create.

 

[shecky]

+1 to dontman. You're lucky you didn't hurt yourself.

 

[alpo]

Ok, that is kind of what I figured. Thanks, everyone.

 

[DeathBrewer]

what? wait...i don't get it. wouldn't there be LESS pressure in the bottle from the same amount of volume and the same concentration of sugar, but more open space for the co2 to go?

please to explain further.

 

[Jaha35]

what? wait...i don't get it. wouldn't there be LESS pressure in the bottle from the same amount of volume and the same concentration of sugar, but more open space for the co2 to go?

please to explain further.

Yes and no haha.

Basically you are still getting CO2 production but because of the excess headspace it does not absorb or get forced back into the beer. So you would still get pressure but low carbonation. You need the headspace to fill with CO2 in order to create the pressure to push excess CO2 back into the beer.

The difference is the pressure in a half full bottle is all CO2 just sitting in the headspace. So all that is holding it in is the glass and it is not really absorbing back into the beer. Thus shaking the bottle would make it unstable and allow for the glass to shatter. Because gasses would be moving around more.

In a full bottle since most of the CO2 is forced into the beer, shaking doesn't do as much because the CO2 has no place to go until you open it.

Ok that is a lousy explanation. It has been a few years since I was in my science classes covering this so maybe someone else can do a better job.

 

[DeathBrewer]

wouldn't shaking the bottle just absorb some of the co2 from the headspace into the liquid?

i think i need to take a class myself...

 

[Jaha35]

wouldn't shaking the bottle just absorb some of the co2 from the headspace into the liquid?

i think i need to take a class myself...

Think of it in terms of flash freezing or heating. When you flash cool or heat a glass you can break it. Because of the violent and rapid temp change you break it.

With carbonation in a full bottle there is high pressure but shaking is not as dangerous because the pressure prevents the CO2 from coming out of the beer/going back in rapidly. The pressure keeps things in line so only few gasses move around unless vigorous shaking is employed.

With a half full bottle you have so much head space that CO2 will rapidly leave the beer, and yes some will go back in but because you have so much open space the pressure of the bottle can change rapidly which can have unknown results. Thus with a half or under filled bottle it is bound to be more unstable than a full one.

Again please bear in mind that this is from a brain 10 years removed from my advanced Bio/Chem classes and I could just be speaking out of my rear end...

 

[alpo]

It is important to realize that pressure and the total kinetic energy of the system are two different things.

After a certain amount of pressure, CO2 will condense and absorb into the beer. If the beer bottle is 95% full, when the air reaches X pressure, all the rest of the CO2 will be absorbed into the beer. Practically speaking, fluids are uncompressable, so all you've got is that 5% of headspace holding a certain amount of CO2 molecules. The air will still be at X pressure, but there is less overall gas in the system, which means less molecules bouncing around and less energy.

If the bottle is half empty, you still remain at X pressure, same as the full bottle, but the difference is you've got 10x more molecules bouncing around.

Remember that pressure is a function of surface area and it doesn't really tell you the whole story of the total energy inside a container.

Also, think about what that means to the glass. X pressure over a larger surface area is a larger amount of total force than the same X pressure over a small surface area. I can press my finger really hard against a window pane in my window and it won't break, but if I take that same window pane thickness and I make the pane 20 feet wide and I have a thousand people press their fingers on it at once, it will break, even though the pressure is the same.

 

[Jaha35]

Thanks Alpo. I think I was trying to get at that but I am just dumb. You said it much better.

 

[DeathBrewer]

ok, that makes more sense. thanks, guys.

 

[Kungpaodog]

It is important to realize that pressure and the total kinetic energy of the system are two different things.

After a certain amount of pressure, CO2 will condense and absorb into the beer. If the beer bottle is 95% full, when the air reaches X pressure, all the rest of the CO2 will be absorbed into the beer. Practically speaking, fluids are uncompressable, so all you've got is that 5% of headspace holding a certain amount of CO2 molecules. The air will still be at X pressure, but there is less overall gas in the system, which means less molecules bouncing around and less energy.

If the bottle is half empty, you still remain at X pressure, same as the full bottle, but the difference is you've got 10x more molecules bouncing around.

Remember that pressure is a function of surface area and it doesn't really tell you the whole story of the total energy inside a container.

Also, think about what that means to the glass. X pressure over a larger surface area is a larger amount of total force than the same X pressure over a small surface area. I can press my finger really hard against a window pane in my window and it won't break, but if I take that same window pane thickness and I make the pane 20 feet wide and I have a thousand people press their fingers on it at once, it will break, even though the pressure is the same.

This is an OK good explanation, but it is a bit off. Now, hopefully I can explain why.

Two bottles will see the same pressure regardless of the amount of liquid in them if they are pressurized to the same pressure.

At work I have had the pleasure of pressure testing pressure vessels (high tech carbon fiber tanks!) and we test them by filling them with water and then pressurizing them with gas. The reason for this is that it is safer, since there is less stored energy in the water under pressure than in the gas. Then when they fail, there is very little explosion, just a little pop.

Think of the pressurized gas as a bunch of little springs. They are very long and can be compressed very far. So if you have a lot of headspace, you have a lot of little springs ready to pop out if you open the bottle.

A liquid, on the other hand, can't be compressed very much at all. Think of it as a huge thick spring that you couldn't move by hand, and it doesn't have much room to compress even if you can put enough force on it. So if your bottle is mostly liquid, there is not much to compress, and very little stored energy in the small amount of compressed gas.

So the bottle is seeing the same pressure (measured in pounds per square inch) at the neck or on the bottom regardless of how much liquid is in the bottle, since any liquid will transfer that force from the gas down into the bottle walls that are under the beer level.

To reconcile this with the theory that a half filled bottle makes a better bomb, I have to make guesses that are beyond my knowledge, but I believe what has been alluded to is that since there is more potential energy in a half-full bottle, it can explode more violently than a full bottle. This still doesn't explain how a half-full bottle will blow up! Has anyone proven this?

Jaha- A liquid will still absorb it's potential amount of any given gas under the same pressure regardless of headspace. The CO2 WILL absorb into the beer, unless there isn't enough pressure to carb the beer, but then this wouldn't have enough pressure to be a bomb!

I'm starting to think that a half full bottle from a properly primed batch will be more dangerous only if it's dropped and the glass breaks in the fall. It may pop loudly, but will still be carbed appropriately, or under-carbed.

So why would a half-full bottle make a bomb?

 

[Jaha35]

Well, you sort of answered your own question as did Alpo.

With the full bottle the limited amount of gas is only pushing on a small amount of the bottle yet with the half full bottle you have more gas pushing on more of the glass. Hence Alpo's explanation of more people pressing on a pane of glass.

Now with pressure you are right that at rest it won't matter but under stress or shaking wouldn't the pressure increase as the stored energy in the water releases?

I would think this would have more variables than just head space but also impurities in the glass, the seal of the cap, etc. I also think if pressure is constant then a half full bottle would be no more likely to explode than a full one unless acted upon, like shaking or disturbing.

As to whether a half full bottle is more violent than a full bottle I can attest, at least somewhat, to the truth of it. While I have never seen a home brew blow up I hav watched other bottles blow up.

Go to YouTube and search for Dry Ice Bombs. It's a simple concept. Fill a 2 liter soda bottle about 1/3rd with water, add dry ice, and cap. Run away and it will blow up. The more water in the bottle the weaker the explosion. This you explained because with more water you have less energy. I.E. less gas. But I have seen some dry ice bombs almost completely filled with water that were capped and never blew up. I would imagine this was because the headspace was not sufficient to stress the bottle and allow enough gas to build up in the first place.

I guess my biggest question about pressure is if the yeast is actively releasing CO2 then wouldn't pressure increase over time after capping regardless of the initial pressure? I mean you are adding more gas to the bottle even though it is capped.

But as to the bombs I think it mainly has to do with more gas pushing on the glass as opposed to liquid and the more space or surface area the greater the risk of a violent explosion.

At the end of the day I would think if you had a fully fermented wort and added the proper amount of priming sugar then you really should not be in any real danger of a bomb barring any major imperfections in the bottle or extreme situations like major fluctuations in heat or cold. You still will probably have a violent burst at opening but you shouldn't have to defend shards of glass.

 

[Terry08]

Thinking about this. I have a Pet bottle of Lemonade I left in the Freezer. The gas has come out of solution and the bottle is quite expanded. Much bigger than a bottle in the fridge so to me this explains the fact that while a good portion of the Co2 is in solution the pressure is normal. But a half filled bottle with airspace does not exhibit the same result, more space to spread the Co2.

Therefore temperature, free space and the amount of asorbed Co2 can have varied results