under and over carbonation

[xscotto]

Howdy from south of Austin,

Most of the beer I bottle is pretty consistent, but occasionally I find one that is either WAY over-carbonated or somewhat under carbonated. I add my melted priming sugar in water form to a bucket and siphon the whole batch into it, and it seems to mix pretty well, so I'd be surprised if there could be any difference in the amount of sugar from bottle to bottle.

There are only two other variables I can imagine:

1. Contamination- perhaps still some beer residue or something?

2. A poor seal on the cap allowing oxygen in during the carbonation process?


I'm pretty anal about sanitizing my bottles, I soak them in bleach water for a few days, rinse them in hot water and then One-Step them. Is it really possible contamination is still in there?

The over-carbonated ones still go "psssssst" and then of course they overflow, so my guess is I do indeed have a good cap seal.

Beyond that- I have no idea. Anyone else?

Thanks,
Scott

[Trogger]

I've never had one overflow, but I have noticed a difference in carbonation levels on the same batch. I don't know the exact cause, but I attributed it to 2 things, without really investigating:

1) Some bottles are put in the fridge earlier than others, thus allowing the other bottles to age/carbonate more before cooling off the yeast.

2) Not mixing as well as I should, even though I mix the warm sugar water into the batch with a spoon while in the bottling bucket.

[BluesHarp]

inconsistant head space...?

[HogieWan]

Originally posted by BluesHarp
inconsistant head space...?

That would be my guess

[BrewDog]

Exactly how warm is the "warm sugar water" when you add it?
It should be cooled to 70*F or less, so that it doesn't kill your yeast.

Otherwise, my guesses would be as you said: loose caps or not mixing the priming sugar in well enough.

One other possibility is that some bottles may be cooler than others. Try to ensure that they are all kept about 70* for carbonation. Putting them on concrete floors, or in a cool draft can inhibit carbonation, too.

[danno]

I disagree with the headspace theory. oxygen is used by the yeast mostly for reproduction purposes, the sugar consumption and carbonation is mostly an anaerobic process, and is tied to the amount of sugar available. so I see two main issues to watch out for, adequate mixing of your priming sugar mixture, and contamination. your description The over-carbonated ones still go "psssssst" and then of course they overflow sounds like a textbook gusher caused by an infection. one thing to remember, you can't sanitize what isn't first already clean... time to get the bottle brush back out...

[brewmonkey]

While you are anal about the bottles how do you sani your caps? I am with Danno, this sounds more like an infection then a carbonation issue.

[xscotto]

Thanks for the suggestions so far.

To answer some questions, I cool the sugar water to 80 degrees before pouring it into the empty bucket. By the time the batch gets siphoned in, it's probably the same room temp, low 70's.

Being anal, I also One-Step the caps before use.

As far as headspace, if all the bottles were lined up, they'd be within a centemeter of each other as far as volume goes. Not much difference there.

Also, I pour the WAY over carbonated ones into a glass and drink them after they calm down, and they taste the same. That would indicate to me that they probably aren't "infected."

My thoughts so far are that perhaps the sugar water really doesn't mix thoroughly, even though the siphoning takes about 15 minutes and the whole mess is churning slowly during that time. I will hand-stir before bottling my the next batch, although still not convinced that's the cause.

Thanks,
Scott

[YamahaXS]

nice description of the priming process. doesn't address variation within a batch though (http://brewery.org/brewery/library/YPrimerMH.html) this source suggests to me that inadequately mixed beer and priming sugar could lead to inconsistent carbonation levels because CO2 levels are very sensitive to relative small differences in the amount of sugar available.

EDIT: a thought just occured to me.

1) if this is related to mixing, then you should see some patterns according to the order in which the bottles are filled.

for example, if the first 12 tend to be over carbonated and the last 12 under carbonated then I would think thats good reason to think mixing is the problem.

[xscotto]

Thanks for the link. Yeah, if only I could tell now which order the bottles were filled in, that probably would clear things up. But it is starting to appear more like an uneven mixture, and I'm planning to persue it that way for the next batch.

Scott

[I'mRocketMan]

Dude- Number the caps with a sharpie sequentially and place the bottles in the case/box/whatever in that order...

You might want to taste test random bottles (or maybe every 10th) for however many weeks you usually do then log the results as you or your test subject's drink them.

Cheers! Rocket

[BrewDog]

Great idea on numbering them.

I also always literally rotated the cases around a quarter turn every couple of days to ensure that they all received the same amount of heat.