Opened a bottle and got a foamcano

Any idea what causes the insane amount of foaming that occurs w/ some bottles? I opened one of my Father-in-law's bottles (Sam Adams Clone) a few months ago and it foamed right out of the bottle. I thought it was altitude, but we're lower than he is. I helped a friend brew a few weeks ago and he had the same problem. It doesn't happen w/ the whole batch, just one.

I want to say I've had this happen w/ commercial beers, but I'm not sure. Any thoughts?

infection, or unequal amount of priming sugar. Either you did not equally mix the priming solution in the beer and some bottles had more than other. Or, some of your bottles were not clean enough and not properly santized.

I rack on top of my priming sugar (after I boiled and cooled it); I don't think that's it. So, I guess maybe I didn't dunk the bottle into my star san all the way or I left a booger in the bottle and didn't notice it.

What about fill level? Could it have been too low and had lots and lots of headspace to build up massive amounts of pressure?

Did you crack them warm or cold? I've noticed that cracking room temp homebrew tends to foam up 10x more than cold.

Headspace was normal and they were defintiely below room temp.

I just had this same problem a couple of weeks ago with Full Moon Winter Ale.
2 or 3 of the bottles from the six pack I purchased foamed like crazy when opened.

I rack on top of my priming sugar

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Do you stir it after you are done?

No. I figured about 5 Gals of beer racking on top of it would do the trick.