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Bottle bomb ponderings

So I am talking with one of my padawans about the upcoming brew day tomorrow. They were reading an article, specifically about mead, that states: “allow 9-12 months to insure you will not have bottle bombs from carbonation”. My response was: “or you can take gravity readings and know way sooner.”

But that got me to thinking about carbonation and bottle bombs.

While I have had batches that were gushers I have never had a bottle bomb (knock on wood). But just exactly how over-carbonated does a beer have to be before a bomb potentially occurs? Now obviously it is better to let fermentation go to completion and then add priming solution to achieve proper carbing volume, but I just found this to be a curious pondering.

For example: If I were to anticipate a batch of anything to end in a FG of 1.014. At what gravity could I safely bottle it without having gushers or bombs? 1.016? 1.020? I guess the question is how many points of gravity = 1 volume of carb? How many volumes of carb can a standard bottle withstand?

Not looking to do any kind of independent scientific testing but just something I guess I never thought about before (especially since I keg everything nowadays).

Call the guys at the EOD school at Eglin AFB, FL. Maybe they can help you with a experiment to quantify that.

It’s a great question that requires a bit of mathematics to answer. Let’s see…

To prime a standard 5-gallon batch of beer, you need to add roughly 3.5 ounces of cane sugar.

Cane sugar contributes approximately 45 specific gravity points per pound per gallon, i.e., add a pound of sugar to a gallon of water and you’ll get a gravity of about 1.045.

So… by adding 3.5 oz sugar to 5 gallons of beer, you’re increasing the specific gravity by about… 3.5/16 lb / 5 gal * 45 ppppg = 2 points, or 0.002.

So… if you KNOW FOR A FACT that your final gravity will be, say, 1.015, then in order to get proper carbonation, you could, in theory, bottle as soon as the specific gravity was 1.017, to get a perfectly carbonated beer without adding any priming sugar.

Now, another thing to consider is that maltose (the chief sugar in beer) is only about 75% fermentable on average, so you might need to divide those 2 gravity points by 0.75 = 2.67. So, for the same example above, you could probably get away with bottling as soon as gravity hit 1.018.

I’ve heard of people trying this in the distant past… but it’s unreliable and dangerous. Before you could ever consider trying such a thing, you would really want to NAIL your process, NAIL your recipe, KNOW EXACTLY what your chosen yeast strain will do for that recipe, and the only way you could know any of these things with great certainty is to brew the same recipe over and over and over like 6 or 8 or 50 times. Then, and only then, could you try your hand at bottling early to see what you get out of it. Otherwise, you’re messing with a very high probability of dangerous bottle bombs. I’ve had bombs happen, and let me tell you… you don’t want those going off in your hands. Thankfully nothing has blown up on me, but it could have, and I was very lucky. After seeing shrapnel up to 20 feet away, I was able to appreciate the danger of the situation and take all the necessary precautions to minimize hazards when the remaining bottles were disposed of.

So… yeah. It could be done. But it’s dangerous if you don’t know exactly what you’re doing. Which would probably apply to about 99.99% of homebrewers who would be interested in trying this.

I had bottle bombs with a batch of stout that I was sure was finished – I had done a fast ferment test that finished at 1020 and that’s where the beer was after 3 weeks. I primed with 3.5 oz of table sugar and a month or so later I had some bombs. I carefully opened one bottle and let it degas. Its gravity was 1012, but that doesn’t necessarily mean that 8 points is the magic explosion point.

Our host has a handy guide that lists maximum recommended CO2 volumes for various bottles ... ioning.pdf

It’s not just overcarbing. Over time, handling the bottles just a little too roughly can develop cracks in the glass. Once this happens all bets are off, even at standard pressure.

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