Bottle bombs are not fun, but if you experiment enough with homebrewing eventually it may happen to you.
My goal here is to explain why the bottle bombs happen and how you can avoid them, as this is not a pleasant experience. Bottle bombs will destroy your precious homebrew, but they may get even worse and hurt you as the shattered glass is a force to be reckoned with.
A bottled homebrew is at risk of exploding in two cases: Too much Co2 which overwhelms the bottle’s pressure levels or gas expansion due to temperature change. Factors like live yeast, bad priming measurements, and bad ingredients may lead to those two cases.
Let’s analyze each possible cause of bottle bombs.
1. Poor bottles and caps
Every bottle has a pressure tolerance and if you create too many Co2 volumes within a bottle, the bottle will only tolerate so much as it was manufactured for before it explodes into pieces. This is the reason why we don’t use wine bottles for beer, sparky mead, or champagne as the glass walls are too thin and it can’t sustain the pressure. While wine bottles are ideal for non-carbonated brews such as wine, we need stronger bottles with thicker walls for carbonated brews.
A standard beer bottle can sustain up to 4.5 volume levels without breaking, and the most carbonated beer styles like wheat beer, Trappist, or Belgian ales rarely go beyond 3.0 Co2 volume, while most lagers and ales fit between 2.0-2.8 Co2 volumes.
Champagne on the other hand is a highly carbonated brew and although most champagnes are around 4.6 Co2 volumes they can reach 6.0 Co2 volumes. For obvious reasons, you don’t see champagne bottled in standard beer bottles, but rather in heavy, tall bottles with a wire cage at the top to hold the cork in place.
So, the conclusion is that you should use standard beer bottles and avoid anything weaker if you are brewing beers, while if you brew champagnes, super-carbonized meads, or ciders use even thicker bottles. Also, avoid any caps that are not firmly sealed with a capping machine or flip-top bottles with included caps.
2. Bad priming sugar measurements
Priming sugar is necessary for the carbonation of your homebrew and no beer or sparky cider/mead would be complete without this process. However, adding too much priming sugar is the top reason why bottle bombs happen.
Sometimes adding a scoop over the desired dose can be too much and exceed the volume the bottle can take. For instance, if the recipe calls for 2.5 Co2 volumes in beer which is equal to 5 grams of priming corn sugar, but you accidentally add nearly 10 grams to a single bottle it will create volumes above 4.5 which is critical for standard beer bottles, and may cause it to explode.
To calculate how much priming sugar you need, refer to a desired Co2 volume for the brew style you are brewing and online priming calculators can be helpful. Bear in mind that these calculators will also take into consideration the Co2 trapped in a fermenter as there will always be some small Co2 added to the bottles on a bottling day as Co2 already got trapped during fermentation and hasn’t fully escaped.
3. Back sweetening
Sometimes a brew should be enjoyed sweet but all the sugars have been eaten by the yeast during the fermentation. Unfortunately, if you keep adding extra sugar the yeast will feast on it forever. So, adding extra sugar or not letting the fermentation complete before bottling means the yeast will continue to eat sugars and produce Co2 within a bottle and the Co2 volumes will raise.
Fortunately, beers don’t need to be sweet so this only applies to cider and mead makers.
Back sweetening prior to bottling without killing the yeast is guaranteed to cause bottle bombs as the Co2 volumes will be so high that no bottles on the market will sustain the pressure. While you can kill the yeast by applying certain techniques, Homebrews can hardly accomplish a sweet carbonated drink and that’s the sad reality.
You see, to naturally carbonate a brew it needs to have live yeast and some sugar, but the problem is how to reach the desired Co2 volume, stop it, and still remain with lots of sugars that will give the brew the sweet taste at the same time.
I can think of two ways, but they are not always accessible to homebrewers.
- Kill the yeast-back sweeten-force carbonation
- Let the yeast live-back sweeten- wait for desired Co2 volume – pasteurize bottles to kill the yeast
The first option means you need a keg and the equipment for force carbonation which most homebrewers, especially beginners don’t have access to.
The second option can work, but it’s difficult to time it, and you need to pasteurize the bottles which are almost guaranteed to cause at least a few bottle bombs even if you know what you are doing, so claiming it for the first attempt can be risky but can work.
4. Heat can cause bottle bombs
When the gas is cooled it contracts, when the gas is heated it expands. The temperature plays a big role in bottle bombs, and while the small variations that happen slowly over time won’t cause a shock, rapidly changing the temperature can cause the gas to quickly expand and shatter the bottle or the cap.
In reality, this will rarely happen if you keep the bottles in one place as the temperature is likely to be constant, but when you pasteurize the bottles this may be an issue.
As I mentioned above, pasteurization is tricky, especially with highly carbonated bottles, and when you increase the heat required to kill the yeast it may break a bottle. To reduce these odds from occurring, you need to slowly heat up the water and make sure the bottles are never in contact directly with the heat.
Can beer bottles explode in the freezer?
Beer can explode in the freezer and it shouldn’t ever be frozen. First, if you freeze the beer, water which is the primary ingredient will expand and shatter the glass, second even if you avoided the bottle bomb it could impact the beer flavors after reheating it and making it worse.
How do you keep a beer from exploding?
Beer shouldn’t ever explode if there are healthy Co2 volumes inside a can or a bottle, but if you leave the beer in sunshine or in a small room that easily heats up like a car it can cause the beer bottle or can to explode. Keeping the beer in a chilled place like a fridge or at room temperature will reduce the odds of beer exploding, but beer should be kept in a cool, dark place if you want to enjoy the best of it.
Conclusion
Bottle bombs are a dangerous and scary experience, so if you ever suspect it may happen wear safety glasses, and gloves, and cover as much skin with the thick leather as possible to stay safe from the hurling glass. I had bottle bombs and fortunately, they didn’t hurt me because I used insulated heat bags with a lid in which I placed bottles and then poured the hot water for purposes of pasteurization.
In less than an hour, I had a few bottle bombs that were so aggressive they almost punched the lid from the top, and tomorrow a few more bottle bombs happened. Another bad thing was the chain reaction as I had 10 bottles in one bag and it must have affected the bottles that otherwise may not have exploded.
I learned the hard way by losing half of my cider that it’s difficult to naturally carbonate and back sweeten the homebrew, and the half that survived was overly carbonated so it gushed so much I would lose the half of a bottle just by removing the cap.
If you want to know more about the ways how to stop fermentation you can find more about it in my dedicated article.