5 Home Brewing Tips to Avoid the Dreaded Bottle Bomb

by Brad Smith on August 27, 2009 · 22 comments


Today we are going to look at how to avoid the dreaded bottle bomb when homebrewing your own beer. I recall my first bottle bomb vividly. It was my third batch of beer — ever. I was not home at the time, but when I arrived back in my apartment, I knew something was wrong. You see, my third batch of beer happened to be a stout.

The bottle exploded in the kitchen and left dark stout covering the walls, counter, floor and cabinets. It was only a 12 oz bottle, but it looked like someone had repainted the kitchen. Glass was also scattered as far as the living room and a small piece had even embedded itself in the drywall. I realized at that point that this homebrewing thing was a lot more dangerous than I had guessed. Someone could have been hurt.

In the years since, I learned quite a bit more about brewing and bottling. I have not had another beer bottle explode since then. I would like to share a few of my tips with you now:

1. Use High Quality Ingredients

The quality of brewing ingredients in the 1980s was nowhere near the quality home brewers have access to today. However, you still need to be careful when purchasing ingredients – particularly those that look like they have been on the shelf for a while. First, always use fresh malts and malt extract. Older liquid and dried malt extract in particular will ferment much more slowly than comparable all-grain wort. Yeast also has a limited shelf life. Liquid yeast is generally of higher quality than dried packets, but it must be stored under refrigeration and must be used in the recommended shelf life. Liquid yeasts are typically dated – so pay attention to the date when you purchase and use the yeast. Old, expired yeast will ferment slowly or possibly incompletely contributing to exploding bottles.

2. Allow the Beer to Ferment Completely

One of the chief causes of exploding homebrew bottles is beer that has not been fully fermented before bottling. Many home brewers are anxious to drink their newest brew and rush it into the bottle too early. The beer then completes its fermentation in the bottle, producing extra CO2 pressure that can cause bottles to fail. Malt extract based beer will ferment more slowly than a comparable all grain beer, so malt extract brewers are at higher risk. Finally, many extract brewers use plastic buckets with covers that seal poorly. As a result, gas may leak out the edge of the bucket rather than through your airlock. A beginner will interpret the lack of airlock activity as an indicator that fermentation is complete, never realizing that the CO2 from active fermentation is leaking from the cover. I usually allow a minimum of two weeks for an average beer to ferment before bottling, and wait a longer period if brewing a high gravity beer.

3. Use Good Bottles, and Inspect Them

A poor quality bottle is a recipe for disaster. Even under normal carbonation, a beer bottle at room temperature can reach 30+ psi. Never use a twist off bottle – they are too thin and your caps will not properly seal. Select the thickest bottles you can find, clean them thoroughly and inspect each of them by holding them up to a light source each time you use them. Immediately toss any cracked, chipped or thin bottles. Consider purchasing high quality reusable bottles from your homebrew store – these are generally better than disposable commercial bottles. If you use them several times, the cost is quite reasonable.

4. Calculate and Weigh the Right Amount of Priming Sugar

Sugar density varies tremendously depending on who made the sugar – one cup of corn sugar from one manufacturer weigh dramatically more than another. Weigh your priming sugar – don’t just measure it by volume. You can calculate the exact weight of priming sugar needed using a spreadsheet, online calculator or BeerSmith.

5. Store your Beer in a Cool Dark Place

Light and heat are natural enemies of finished beer. Light and heat break down critical flavor compounds, promote additional fermentation and increase the CO2 pressure in the bottle. As you heat a bottle of beer, it also dramatically increases the pressure in the bottle itself. Store your beer in a cool dark place to avoid bottle bombs and preserve its natural flavor.

Thanks for joining us on the BeerSmith Home Brewing Blog. If you have additional suggestions for improving your bottling, or ideas for future articles please leave a comment. As always, feel free to subscribe, share this article with a friend or bookmark it on your favorite social website.

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{ 18 comments… read them below or add one }

BrewToppers August 29, 2009 at 11:47 pm

Great article! I think I’ve been guilty a few times not letting my beer completely ferment. My next brew I’m going to be a bit more meticulous about these things!

Brewologist August 31, 2009 at 11:13 am

Very good advice! Helpful tips. Fortunately I’ve never experienced bottle failure, but I once had my old bucket fermenter blow it’s lid and spew hops and wort all over the wall. That bucket had a good seal, no leaking CO2 there. Hehe.

I’ve been close though. I noticed the caps on bottles from one batch of beer starting to rise up, a sure sign of too much preasure in the bottle. I knew that batch was a goner, so I just opened them up and poured them out. The beer did foam out of the bottles like crazy upon removing the caps.

Now I leave a minimum of two weeks for my lower gravity ales to ferment, and after about 10 days in the bottles I’ll chill them to halt the carbonation process. Longer in the fermenter and proper priming measurement are critical to avoiding exploding bottles!

Beantown Brews September 11, 2009 at 1:07 pm

I think making sure that you adequately prime your bottles and proper storage are probably the biggest points to consider. Great stuff.

Scott-TheBrewClub October 7, 2009 at 4:25 pm

Good article. As someone just getting into home brewing, the concept of ‘bottle bomb’ is one I’d like to avoid!

GregK March 18, 2010 at 10:07 am

Great article. I had my share of bottle bombs when I started brewing.

One time I gave a bottle of stout to an attorney who was working with us on one project. A couple months later he called to tell me it has exploded on his desk! Yikes!

Anyway, the other thing to note is that you can be sure the beer is finished fermenting if you check the gravity and (1) it’s close to your target final gravity, and (2) it stays there for three days.

The trouble is that all that goofing around with the hydrometer is a mess and might introduce contaminants into your beer — which is a great reason to get a refractometer. You only need a drop or two to get your gravity. I recently found one on eBay for about $25.

One other tip from “Homebrewing for Dummies.” You can get a decent guess at what your final gravity should be by knocking off the 1 and multiplying it by .35, then adding the 1 back on.

So if your O.G. is 1.050, multiply 0.05 by 0.35 to get .0175. Your final gravity should be in the neighborhood of 1.018.

Tesilential July 27, 2011 at 5:14 pm

^^^ thats really inaccurate. My 1.05 brews finish at 1.01 or below. An FG of 1.018 is very high and expected for big beers (1.07+) like some stouts, porters, or barleywines. Lots of crystal malt will raise FG as well.

You need to take a hydrometer sample, refractometers are for brewday, they are MUCH less accurate after fermentation has begun.

Peter Owens October 19, 2012 at 11:32 pm

Mostly good advice, but for newcomers several things which I believe are important are missing:
1) Always taste your beer before making that final decision to proceed to bottle, beer that has fermented out has a taste that will indicate trouble if off flavours, sourness or sweetness is detected. Residual sweetness is a clear indication that fermentation may not be complete so only proceed after a hydrometer check.
2) You may have a hydrometer, but find it confusing to use & have put off actually using it. Some tips:
Only use a “Beer Hydrometer”, they are purpose built & available from all decent local home brewshops.
Always purchase a hydrometer flask suited to the hydrometer you own. This will generally be glass or plastic (better & cheaper) about 40mm in Diam & about 250mm high. This way you don’t waste too much beer & you can discard after the measurement is taken.
Study carefully the hydrometer scale & test with tapwater which will read 1.00. If you dissolve some salt in the water it will become denser & your reading will climb above 1.00. Recognise that after fermentation alcohol will have been produced, which tends to lower the gravity, so a fermented out beer will be not measure much above 1.00 & typically for ales, you will see 1.01.
Most fermentors have a bottom drain tap & I recommend drawing the beer sample SLOWLY from this tap. I have found it is not necessary to remove the airlock so the procedure does not put your brew at risk of infection. Some yeast is inevitably drawn off in this method but I have found this does not affect the readings much so you rely on them for a bottling decision.
3) Bottles: glass is always best BUT plastic reusable bottles do not make bombs. My experience indicates the such plastic reusables are good for only about 6 uses because you will find that the beer eventually etches the plastic at the beer – gas interface. I have had friends who have sought out green used empty plastic lemonade bottles, salvaged by cleaning with full strength pool liquid chlorine. Typically these are a bit big being generally 1.25 litres – but if you are on a tight budget?? BTW you can reuse the screw on plastic tops (properly sanitised) almost forever.
Hope this minor detail stuff may help.

Kasey April 3, 2013 at 1:07 pm

What a information of un-ambiguity and preserveness of valuable familiarity concerning unpredicted feelings.

Frank February 6, 2015 at 12:22 am

I experienced bottle bombs once – in the middle of the night and pitch dark we were woken by the sound of explosions and smashing glass – I thought someone was throwing rocks through our bedroom window – is this WWIII ?!?!? – freakout !

got up – dazed and confused – found the sound coming from our laundry – where I had stacked cases of fresh-bottled home brew beer – I had bottled it a little early – guess primary fermentation had not finished – so with the addition of secondary sugar it created mini-grenades – I couldn’t go in there until the bombs stopped exploding – helped by the fact that cases on top were pressing down on bottles underneath – when I finally ventured in, there were deep scars in the ceiling plasterboard from glass shrapnel fragments all over the place, and I spend several hours afterwards picking up all the glass fragments out of everywhere and sponging beer out of our lounge room carpet.

That’s a one-time lesson I’ve taken care to avoid ever since – now my rule of thumb is wait 9-10 days for primary fermentation – tho’ after 99 batches my last batch was kind of ‘off’ – suspect an uncleaned tap internals – I got a new vat and touch wood I’m good again.

ashley kent carrithers January 16, 2016 at 5:59 am

Hi – not so much a comment as wanting to take advantage of you experienced folk to ask the following question; can I use a 4.675 liter thick wine bottle (demi-juana from Argentina) with a big cork in it to bottle? I am concerned that the cork may not be secure enough. P.S. we have an estancia in Patagonia and tend to drink a good gallon at a time of beer – hence the large bottle, plus it is attractive. Thanks, Ashley

Dane Garber April 8, 2016 at 2:08 pm

My normal practice is primary for 1 to 2 weeks, cold crash for 1 day, let beer come back to room temp for a day ( I have found that when using a bottling bucket, room temp beer helps with even distribution of the sugar solution during bottling), then bottle and let stand at room temp for 2 weeks. A little tip for those who use plastic bottles. After filling your bottle, put the screw top on half way and squeeze until beer comes out and then tighten. This will remove the oxygen from the bottle and the bottle will expand back to its normal shape within a week and become nicely carbonated, if you use the right amount of sugar of course. By the way, my favorite plastic bottles are 16.9 oz root beer bottles and 2 liter pop bottles are great if you know you are going to drink at least 4 pints. Any time I use something larger than a pint, I will slowly pour into a growler, leaving the yeast sediment behind and then serve from the growler.

THess July 1, 2016 at 1:07 pm

Ive never had a bottle bomb in 20 years, but I have had a few close calls.
You can tell which ones are the close calls when you open a beer and you get a Las Vegas style fountain.
Ironically, Ive always used plastic twist off bottles, which probably saved me from an explosion because they will expand
or eject the cap long before you get a “new paint job”. Yes its still a bad mess, but its going to be limited to the area of
the bottle, you wont have shrapnel in the walls, and “as far as the living room”.

Frank Leonardo August 24, 2016 at 11:07 am

Surprising no one mentioned the head space in the bottle. It should be about 1″to 1.25″.
Any less you won’t get good carbonation, any more you may have a bomb!

Frank Leonardo August 24, 2016 at 11:07 am

Surprising no one mentioned the head space in the bottle. It should be about 1″to 1.25″.
Any less you won’t get good carbonation, any more you may have a bomb!

Adrian Tinca November 25, 2016 at 6:25 am

Hi, I brew my first all grain brewing kit and it’s been 15 days since it stays in the fermenter. I wanted to bottle it today but I saw some very little bubbles coming up in the fermenter. I took away the airlock, put it back and in 5 minutes it created a small quantity of presure (enough to move the disinfectant from the first chamber to the next one). My kit didn’t come with a gravity measuring tool so I have no clue on what to do next. I keep on waiting or could I bottle it?
And another question – my recipe says 30 grams of sugar for 5 litres of beer, but for sure I lost some (yeast on the bottom takes a good amount of space) – I need to transfer the beer in another pot, measure the quantity and then determine the sugar it needs?
Thank you,

dom November 29, 2016 at 9:28 am

^^^ I put the beer in bottling bucket, check how much there is and then use a priming calculator to see how much to add for the style of beer. Also How would you know the precent, without a hydrometer?

Nelson January 15, 2017 at 11:22 am

Our brew is still fermenting after 5 weeks. The temps are a bit on the cooler side but non the less is still showing bubbles.
How do I know when it is too long or do I need to wait until it is completely done fermenting? Seems to smell ok when checked.

Tex Hooper March 4, 2021 at 7:04 pm

You make a great point about how dried malt extract is different than all-grain wort. I recently had my first beer and have discovered I like dark brews. I’ll have to go to tap rooms that have special fruit brews as well.

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