Don't partially fill a bottle...

The last batch I bottled was a Haus pale ale, and when I got down to the last bit in the bottling bucket it wasn't enough for a full 12oz bottle. So I filled a little over half of a bottle. Not knowing better I figured what the hell I have the caps I'll just throw one on it and let it sit and see how it carbs up.


Take it from me, don't cap a bottle with that much head space.

Oh my....it was SOOOOO heavily carbonated.

I'm assuming due to all the compressible air space, the CO2 production went wild.

Upon opening the bottle there was a loud / long pressure release Psssssssst.

The bottle didn't gush so I was hopefull. I got out a glass and SLOWLY poured just a small bit into the glass, barely an ounce. As soon as the beer touched the glass it filled the entire glass with foam. Kind of like that spray foam you use to seal houses...


Need less to say I let it sit out over night and drank it the next day and it still had carbonation in it! The flavor was still quite over powered by the carbonation.

I think you're lucky you didn't get a bottle bomb. There have been several stories of half-filled bottles assploding on here.

Yeah seeing how carbonated it was, I think I am lucky.

I thought bottle bombs were only from adding too much priming sugar...

it wasnt because of the head space...it was because the last bottle gets more sugar due to the sugar settling to bottom of the bucket

BobcatBrew said:

it wasnt because of the head space...it was because the last bottle gets more sugar due to the sugar settling to bottom of the bucket

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Then why doesn't the last bottle of every batch do that? No, a partially filled bottle will overcarbonate and possibly blow up.

ChshreCat said:

Then why doesn't the last bottle of every batch do that? No, a partially filled bottle will overcarbonate and possibly blow up.

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It does for me....

I found that when you have to tip the bucket you get sugar that settled to the bottom--that's why I stir it again mid run. I have 1-2 inch head space depending on the style of bottle and never notice a difference. I think oxygen is the bigger concern with too much head space and that is even over stated.

In a normally filled bottle, the volume of compressed gas in the headspace is small. When you open the bottle, the pressure is released and the gas escapes. A normal PSSSST sound. The rest of the carbonation is in solution and comes out through the normal bubbles.

When you under fill a bottle, a much larger volume of gas in the bottle is now pressureized. It will be under a smaller pressure because of the less amount of CO2 produced by the beer, but when you open the bottle, all of that gas wants to come out, several times the amount of a normally filled bottle. That's when you get the big explosion of gas.

BobcatBrew said:

It does for me....

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You need to mix your priming sugar better then. Or... this would be a good excuse to start kegging!

I do keg...and it has nothing to do with how well I mix. if anything it could be that its taking too long to bottle allowing the sugar to settle. See previous post about re-mixing half way through

I don't think kegging is worth the price. I would like to have a few taps for quaffers but bottling is just the price of the caps and about an hour a batch. I doubt kegging is going to save all that much time.

Brewsmith said:

It will be under a smaller pressure because of the less amount of CO2 produced by the beer, but when you open the bottle, all of that gas wants to come out, several times the amount of a normally filled bottle. That's when you get the big explosion of gas.

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Yes, there is more gas in the head space which escapes when the cap is removed. However, every other bottle in this batch was equally carbonated, I stirred several times and racked very slowly. Of this I'm certain.

I still think my head spacing was the culprit.



As pressure drops because of the larger compressible head space, the volume of the produced CO2 increases to maintain equilibrium with amout of substance, gas constant, and temperature.

Once sugar is dissolved, it's not going to settle out. The can of Coca-Cola isn't thicker at the bottom, you know? When the sugar's in solution, not in suspension, it's not going to settle.

The priming sugar was dissolved in hot water then cooled and racked on in a syrup form. So I'm pretty confident it was mixed well.

The thing is the sugar is not in solution, it's only suspended. It would take more time to become a solution. Stirring helps but still you have spots with more than others. Ever read about a extract batch with false gravity readings--same thing. Stratospheric conditions will also happen.

the_bird said:

Once sugar is dissolved, it's not going to settle out. The can of Coca-Cola isn't thicker at the bottom, you know? When the sugar's in solution, not in suspension, it's not going to settle.

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an unfermented sugar solution is not denser than than the beer you mix it in? I would say it is...I would also say that would cause it to sink to the bottom

BobcatBrew said:

an unfermented sugar solution is not denser than than the beer you mix it in? I would say it is...I would also say that would cause it to sink to the bottom

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I understand what you are saying, but how can I account for every other beer in that batch having just the right amount of CO2, but this half filled bottle to have coincidentally way more.


I suppose one could test these theories, by bottling a beer half full somewhere during the middle of the bottling process and see what it's carbonation levels are...

It was the last one. I don't under fill and I've noticed the last one over carbs anyway. Now I stir longer and more often.

Am I the only one that puts that partial bottle in the fridge and drinks it once it's chilled?

mkory said:

Am I the only one that puts that partial bottle in the fridge and drinks it once it's chilled?

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Sweet and flat?

mkory said:

Am I the only one that puts that partial bottle in the fridge and drinks it once it's chilled?

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The low carbonation and the priming sugar make it too cloying for me. I might taste it before I dump it down the sink.

mkory said:

Am I the only one that puts that partial bottle in the fridge and drinks it once it's chilled?

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Probably. I doubt most folks bother chilling it......

Honestly, flat sugared beer never appealed to me so when I have less than a bottle's worth left in the bottling bucket, it goes down the sink.

Very first batch I had one like that-didn't explode, but jaysus was it a bubble-monster. More suds than brew!

I don't know why it happened, but I'm 100% sure that having the extra headspace is NOT the culprit. The extra headspace will, without doubt, reduce your carbonation level if the concentration of priming sugar is consistent with the rest of the batch.

The amount of priming sugar that you add is figured based on getting a certain number of volumes of CO2, probably ~2.5 vols, into a full bottle of beer. Therefore your typical bottle conditioned 12 oz. bottle has enough priming sugar to generate 30 oz. of CO2. Since there is generally a pretty small amount of headspace in a full bottle, 95% of the CO2 goes into solution.

If you put 6 oz. into a 12 oz. bottle, there are 6 oz of headspace, and the priming sugar will only generate 15 oz. of CO2.

So, with a full bottle you're forcing 30 oz of CO2 into a space <1 oz, with a half full bottle you're forcing 15 oz. of CO2 into a 6 oz space. It's pretty clear, more CO2 will make it into the beer in the case of the full bottle.

I believe it's the extra headspace because it's even been reported when bottling from a keg. The poster left too much headspace when filling bottles from a normally carbonated keg and after a short while they were seriously overcarbed. Anyone remember who that was?

IXVolt said:

As pressure drops because of the larger compressible head space, the volume of the produced CO2 increases to maintain equilibrium with amout of substance, gas constant, and temperature.

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yeah that's right, just got confused the way it was written.

Since this is all in equilibrium when n is increasing (yeast producing CO2 and increasing the moles of CO2 gas) therefore the Pressure also increases all the while the liquid is absorbing some CO2

This is all of course assuming "ideal" conditions

I always do that lol. I've never had bottle bombs, but I know when I have a beer like that I open it at the begining of the night and just let it sit a couple of hours. Why waste beer? I don't get scientific about it. Unless it explodes, it's just more fizzy than the others lol.

IXVolt said:

Need less to say I let it sit out over night and drank it the next day and it still had carbonation in it! The flavor was still quite over powered by the carbonation.

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back to the OP -
regarding letting it sit - another option would be to stir quickly with a piece of flatware - causing more bubbles, certainly, but out-gassing the product. when the foam settles, test. Stir again if needed.

Using this method, you don't have to wait...