Bottle bombs from under-mixing sugar?

[dr_bollinger]

This is my 1st post regarding my 2nd ever batch.

My issue is that my batch seems to be not excessively carbonated, but I just had a few bottles break in storage. I'm wondering what the problem could be.

I had a box in the basement with 12 650 ml bottles stored in it. 3 adjacent bottles had their bottoms broken off (quite cleanly). My theory is that 1 bottle went and the others followed. Apart from this issue, the beer seems highly carbed but within the bounds of reason (and safety!). When I open a chilled bottle, it doesn't overflow from the bottle, and pours with a bit too much head but not more than I've had with some commercial beers.

I can think of a few potential causes of the explosion(s):

1. There may have been fermentable sugars when I bottled. I tried to get my the batch around 2.5 vols of carbonation, and used the Brewer's Friend calculator to calculate how much priming sugar to use. I was fairly sure that fermentation was complete because I bottled 3 weeks after brewing, because I fermented at a fairly high temperature (around 65-68F), because airlock activity had slowed to nil, and because the gravity was around my expected FG, 1.012 (for a session IPA with an OG of 1.050). However, I only checked the gravity the two times, so I can't be sure if the gravity was still decreasing.

2. The temperature in my basement has increased up to like 75F. Perhaps even at 2.5 vols that is too hot? The temp has been around 70 lately.

3. The priming sugar may not have been evenly distributed throughout the bottles. I added the sugar water to the bucket first and then racked the batch onto it. I didn't mix the batch in the bucket, but assume that racking it on top of the sugar would accomplish that.

4. The bottles may be defective. I bought the bottles from my LHBS, and they seem solid. They are 650 ml classic brown bottles.

5. I may have an infection. I don't think so, though. I never saw any signs of one.

In any event, I moved the remaining bottles from that batch either into the fridge to cool them, or into a cooler to prevent a mess if more explode. Hopefully they do not!

Any ideas???

 

[worlddivides]

3 or 5 seem most likely to me since I don't think there'd be fermentable sugars left after a full 3 weeks of fermentation (well, at least not for the yeast strain that you picked), assuming the yeast hadn't been made dormant (which is unlikely since you said it was stable at 1.012). There is, of course, the possibility that there was an infection that was introduced that kept fermenting down. Any wild yeast, of course, could keep fermenting down further and further.

I've personally never experienced something like #3, but I have heard of cases where bottles were unevenly carbonated and I can definitely imagine it as a possibility if you didn't mix the priming sugar and the beer together in the bottling bucket. I always mix them with a large metal spoon after the beer and priming sugar are both completely in the bottling bucket, and then I mix them after each 4 bottles that I fill. That's probably paranoid overkill, but I do it for my own peace of mind.

 

[dr_bollinger]

3 or 5 seem most likely to me since I don't think there'd be fermentable sugars left after a full 3 weeks of fermentation (well, at least not for the yeast strain that you picked), assuming the yeast hadn't been made dormant (which is unlikely since you said it was stable at 1.012). There is, of course, the possibility that there was an infection that was introduced that kept fermenting down. Any wild yeast, of course, could keep fermenting down further and further.

I've personally never experienced something like #3, but I have heard of cases where bottles were unevenly carbonated and I can definitely imagine it as a possibility if you didn't mix the priming sugar and the beer together in the bottling bucket. I always mix them with a large metal spoon after the beer and priming sugar are both completely in the bottling bucket, and then I mix them after each 4 bottles that I fill. That's probably paranoid overkill, but I do it for my own peace of mind.

Thanks for the reply!

Yes, I suppose that I should mention that I used White Labs Vermont Ale, so 1.012 seems like a pretty reasonable FG.

As an update, after another 2 days, I've had no further breakage.

I'm still very perplexed -- all of the bottles that I have opened (maybe a third of the batch so far) have been relatively consistent in terms of their carbonation (high but not crazy). It makes me think that maybe the bottles were defective.