Ask Mr. Wizard

Bottle Bombs


Mark Conner - Vancouver, Washington asks,

I have been bottling in bombers for three years without issues. Following my normal process I have had four detonations and everything has been a foam fountain for my last three batches. What could have changed to cause this?


Bottle bombs are really scary because glass shrapnel can cause severe injuries. The first question that always comes to my mind when hearing about this problem is “how old is your glass?” Some brewers re-use bottles over and over again and eventually the bottles begin to fatigue and fail. Breweries using returnable glass bottles have glass inspection systems to help spot glass with fractures and remove suspect bottles prior to filling. However, I don’t think this is your problem because of the foam fountains you mention.

If you were a new brewer I would suggest that you get control of your bottle conditioning, but my gut tells me that you have bottle conditioning figured out and you are not simply adding too much priming sugar. I think your problem is with super-attenuation. This happens when something in your bottle is able to convert unfermentable dextrins into fermentable sugars. And the most common critter that causes this to occur is Brettanomyces. Considered a wild yeast by most breweries, Brettanomyces, or simply Brett, is increasingly being welcomed through the front door of many a brewery.

The problem with Brett is that this yeast is hard to kill and is a whole lot like garlic, in that a little bit goes a very long way! A few viable Brett cells in a beer bottle will slowly find food from sources unusable by “normal” yeast. Over time, Brett will cause bottles to become highly carbonated and turn them into the occasional grenade. I personally like Brett when I want certain aromas and flavors. But when unwelcome, this yeast is a real problem and I have a hunch that this may be the source of your problems.

If you have not been dabbling with Brett, I suggest verifying that the beers you package are indeed done fermenting prior to packaging (research “forced fermentation”), double-checking your dosing procedures and checking the glass you are using.


Response by Ashton Lewis.