Beer getting more carbonated with time?

I've been brewing for a little over a year now. Lately I've noticed that some of my brews seem to get more carbonated the longer they stay in the fridge.

For example, I just opened an oatmeal stout that I brewed and bottled last spring. It gushed out and made an absolute mess! I've been drinking this beer off and on since May and the carbonation has been spot-on. This was among the last of that batch, bottled in a 22 oz. "bomber bottle" and stored in the fridge at about 40F since it came off carbonation.

I've had similar experiences with a couple other brews that have been in storage for several months. Why in the world would these beers erupt like that?

Any ideas or comments would be appreciated.

1st two things that come to mind:
- Do you use a hydrometer to determine when fermentation has completed?
- Do you use a priming calculator to ensure the priming charge is correct?

Cheers!

Early on in my brewing hobby I gave my father a bunch of bottles I had saved up of beers I had made (about 20-30 bottles) when I moved apartments in college. He likes to keep his house warm and Texas summers get a wee bit toasty. About 8 of the bottles exploded over time.

This was likely due to incomplete fermentation due to under pitching yeast, which meant it was slowly fermenting over time more and more.

Unless you "kill" the yeast or remove it somehow, there will be a little fermentation going on until there is no more sugar for it to eat.

Oh, my best one: when I was 17 or so and still living at home I actually had 4 little 1 gallon party kegs like you can get Heineken in nowadays. I made a brown ale and put it in my brother's closet to card (he had moved out 2 years prior).

Well, 4 weeks later my mother is looking for something in his room and opens the closet: yup, the keg had exploded. I don't mean like a little edges torn and spilled, the whole thing was torn apart at the top and was only about 1/3 full.

Side note: those kegs were awesome. I lost my last one to Katrina (it was at my brother's house, he drank the contents after he got back 6 months later, but never returned the keg).

day_trippr said:

1st two things that come to mind:
- Do you use a hydrometer to determine when fermentation has completed?
- Do you use a priming calculator to ensure the priming charge is correct?

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No, I haven't gone that scientific with it. Local brew shop said use 5 oz. for most batches. I like to use a little less as I prefer English style beers that are only lightly carbonated. Typically add 4 - 4 1/2 oz. dextrose priming sugar for a 5 gal. batch.

I was inclined to think that a lack of complete fermentation was the culprit. However the biggest problem batch so far has been a batch of brown ale that sat in the fermenter for well over 30 days before I bottled it. I'm having trouble believing that after that long in the fermenter there was any sugar left in the beer at all.

When I used to bottle I had the same thing happen but only with beer that were stored warm.

gometz said:

Unless you "kill" the yeast or remove it somehow, there will be a little fermentation going on until there is no more sugar for it to eat.

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This is not true. Different yeast strains are able to consume sugars of varying degrees of complexity. For example, English and Scottish strains generally are less attenuative, thus will not ferment a beer to as low a final gravity as say, a typical American strain (or, in an extreme beer yeast example, Saison strains). There are MANY commercial beers that are bottle conditioned and unpasteurized that will not have this happen.

Once yeast has finished consuming the sugars that are available to it, it will be unable to consume more. Residual sugars will NOT ferment unless another microorganism is there to consume them. Brettanomyces, Lactobacillus, Pediococcus, etc, *WILL* consume these long-chain sugars but will take time to do so.

In short...if you've got "some" bottles gushing after the beer has been bottled for a few months or more, you've got an infection going on in those bottles.

If you've got gushers after a week or two, odds are the co2 produced during bottle conditioning hasn't been fully dissolved into the beer yet. Let the bottles hang out in the fridge for a few days and it will happen.

cfonnes said:

When I used to bottle I had the same thing happen but only with beer that were stored warm.

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This might be the issue. The only storage area I have for my beer is in my office in the house. Typical summer temps inside run from 78 - 82F. Most of the beer I've had this problem with were stored inside at those temps or were beers that I only held for 2 weeks in fermentation before bottling. Sounds like there might actually be two potential problems here.