So this has never happened before, but I now have had two 12 oz bottles blow up on me. Damn, what a mess. I was using ordinary long neck bottles, regular caps, but it was a relatively high gravity beer (approx. 9%). I used about 3/4 cup of priming sugar, which is less than I would normally use.
Does the higher gravity create the risk of bottle bombs?
What can/should I do now to prevent more? I washed my survivors off and put them in my beer freezer and adjusted the temperature down to 42 degrees. My thinking is that a cooler temperature is going to depress the molecular activity and hopefully it won't be banging around to create shattered glass. Is this sound? Any other suggestions for saving the rest of the batch?
Thanks for any who have some advice.
I think what you've done is probably the best you can do. I don't think the beer will freeze if you lower the temp to 32 or even 30 degrees, which is what I would probably do.
I think what's happening is you have too much residual sugar or priming sugar in the bottle and the yeast is metabolizing it and creating too much CO2. So the low temps should kill off the yeast and arrest the fermentation.
Another possibility is contamination. So open a bottle and taste it. If you get a cabbage or other unpleasant aroma, you might open a few more bottles and see if it's just a few dirty bottles that were contaminated or whether the contamination came from a source that affected all the bottles. But if the beer tastes ok to you, then I think you've solved the problem.
The extra sugar can come from not letting the beer finish fermenting, or by adding too much priming sugar. Hydrometer readings before bottling can give you an idea if the beer has finished. Normally you're looking for about 75% attenuation. So if the beer started at 1.050, you'd be looking for 1.012 to 1.014 before bottling, depending on the recipe. If you take a series of hydrometer readings, you can see when the numbers stop going down.
Of course, you use a lot of beer that way. But you also get to taste it as fermentation progresses and that teaches you how to tell when the yeast have finished the beer. I enjoy mildly carbonated, freshly fermenting beer, something you, the brewer, are the only one to taste. After a while you'll be able to tell if the beer is done merely by looking at the beer in the fermenter.
I just re-read your post and saw it was a high gravity beer. That makes it a bit less likely that yeast are responsible because just getting high gravity beers to finish is challenging because the yeast poops out. Bottle carbonating is even harder for the same reason. I think, though, that the 75% attenuation rule still applies. If the beer hadn't finished before bottling, that could explain the explosions.
My direct answer to your question, then, is that higher gravity beers are less likely to create bottle bombs because just getting them to bottle carbonate is difficult.