Homebrew Beer Explodes When Opened (What to Do About it!)


The dreaded bottle bomb. Many people have probably heard a story or two about some crazy homebrewer that had some exploding bottles of homebrew go off in their garage and got a good laugh, but it’s no joke if you are the one making the beer! Although I haven’t had this problem before, I want to explore why homebrew beer explodes when opened so that others can stay clear as well.

Homebrew beer will explode when opened if there is too much carbonation inside the bottle. This extra carbonation could be from an infected beer, a problem with the priming sugar, or because it’s not quite finished conditioning yet. Proper sanitation and brewing techniques can likely prevent this issue from happening.

As is the case with most homebrewing problems, the answer is easy to say but the devil is in the details. Let’s jump into why your homebrew exploded, what to do if you have a batch of homebrew gushers, and how you can prevent the problem from happening with your next batch!

Why did my homebrew beer explode when opened?

If you are sitting at the keyboard with foam in your face right now from exploding homebrew then you’re probably wondering what happened and why.

You’re probably also thirsty.

There are really three primary reasons that you had a homebrew gusher, but the actual cause is always too much CO2 or other gas being produced inside the beer bottle during conditioning. Eventually, that extra gas is going to create so much pressure that the bottle cap will fly off, the bottle will break, or you’ll have a gush of beer rush out when you open it.

Trust me, a gushing beer is the best possible scenario that you could hope for when it coming to exploding homebrew. Let’s check out those three reasons.

You didn’t ferment your homebrew long enough

During active fermentation, the yeast is busy eating up all of the sugars inside the wort and converting them into alcohol and sweet, delicious flavor. One by-product of this process is CO2. It’s usually very obvious when it’s happening because you’ll see bubbling in the airlock and foamy yeast churning around inside your vessel. Once this process slows down, however, it’s less obvious that fermentation is still happening. Many homebrewers can get tricked into thinking it’s done at this point when it isn’t.

The only way to properly tell whether or not your beer has finished fermenting is to take daily readings with your hydrometer to determine the final gravity and compare it to the recipe. If the gravity of the beer hasn’t dropped for three days in a row and checks out against the recipe, it’s probably done.

If you start bottling your beer when fermentation is still happening and there is still residual sugar inside the wort to process, you are going to have a problem because all of that CO2 being produced has to go somewhere. To make matters worse, you also added priming sugar to the wort before you transferred to the bottles so you gave the yeast even more fuel to keep going.

Your beer became infected at some point

When a beer is infected by bacteria or wild yeast, one of the most common side effects is exploding beer bottles or gushers.

Normal brewer’s yeast has a certain attenuation profile that determines what percentage of sugars it will consume inside the wort, and it varies from strain to strain. The yeast you are using to brew will almost never consumer ALL of the sugar inside the wort, but instead, it will leave some behind to help create the correct flavor profile. Once the yeast finishes eating their fill they will shut down, clump up together, and then fall to the bottom of your fermentation vessel.

What’s left is delicious beer!

Wild yeast, on the other hand, will usually go a little crazy inside your wort and often consumes a way higher percentage of sugar than the yeast strains we know and love. If you are taking readings during fermentation and the final gravity seems too low, this might be the culprit. At that point, you’ll need to continue to watch for the gravity to stabilize and make a decision about what to do from there.

I go into more detail with subject in my post on why homebrew beer tastes sour which you can check out here.

Unfortunately, if the infection happens during bottling, you would have no way to know what is happening. Instead, your first sign will likely be a gusher or exploding bottle as the wild yeast continues to over-ferment inside the bottle and produce CO2 and other gases.

Something went wrong with your priming sugar on bottling day

Even if your fermentation was truly complete and you managed to avoid infection you could still experience gushers if you mess up your priming sugar during bottling.

Typically, you’ll mix your sugar into a little boiling water and then pour it into the bottom of what will be your ‘bottling bucket.’ From there, you’ll siphon all of the beer from your fermenter into the bottling bucket, taking care not to splash and letting the beer mix itself as it fills the bucket. Once the beer is inside the bottles, the tiny bit of residual yeast still hanging out in the wort will reactivate to eat the sugar, creating enough CO2 to carbonate the beer.

You can run into trouble if you use too much sugar or don’t mix it properly because you’ll end up with too much CO2 converted inside the bottles. Even worse if it’s a mixing issue because you might be unsure of the cause if only some homebrew beer explodes when opened!

How to prevent exploding homebrew next time

Now that we understand WHY your homebrew beer explodes when opened we can work to prevent it next time. Fortunately, these solutions are all straight forward and really just require you to pay more attention to what you are doing during every stage of the brewing process.

Leave your beer in the fermenter longer

Like I said before, you cannot move a beer from the fermenter until the process is done.

In general, you should expect fermentation to last at least two weeks. Even though it might appear as though the yeast are done working after just a few days, they are still cleaning up the wort by removing their own by-products and continuing to refine the overall flavor of the beer. Over time, the yeast cake will fall down to the bottom of the fermenter and the beer will appear to clear up as well (more or less depending on the yeast and style).

Once you see all of the outward signs of a complete fermentation and it has been at least two weeks, you can take a sample of the beer to taste and measure the gravity. If the beer tastes like beer, and not sweet, that’s a good sign! Once you have the gravity reading, compare it to the recipe and see if it’s close. It might be a couple of points off in either direction, especially if your original gravity was off due to a problem with the brewing process. Take note of this reading and take follow-up readings for two more days. If the readings are the same for three days in a row and they make sense compared to the recipe, it’s probably done.

Take another look at your sanitation

The best way to avoid an infected beer is to use proper sanitation.

This means properly cleaning (to remove visible dirt or old beer) from your equipment and then sanitizing it (to kill bacteria and wild yeast) before each use. You’ll need to pay extra attention to anything that touches your beer after the boiling process because once your wort has cooled, there won’t be any other opportunities to kill off a bug in your beer.

Here is a general list of everything you’ll need to check:

  • Wort chiller
  • Any spoons or other utensil used to stir cooling wort
  • Fermenter (and the lid if you are using a plastic bucket)
  • Airlock
  • Spigots, valves, and o-rings
  • Tubing
  • Siphon
  • Thermometers
  • Bottles
  • Bottle caps (easily forgotten about!)

DO NOT SKIP SANITATION!

You’ll need to invest in a quality unscented detergent for your cleaning and an approved sanitizer such as StarSan or Iodophor to handle your sanitizing.

Pay more attention to your priming sugar

If everything is good leading up to bottling day, don’t let your priming sugar cause you problems!

Most recipes and kits will include the correct amount of priming sugar for the job, but always check that you are using the correct amount. If you are using brewing software or making your own recipe, you’ll need to be doubly careful. Any fermentable sugar can be used for the priming process, but the most common ones are cane sugar, corn sugar, and brown sugar. If you are buying a kit, it will almost always be cane sugar because it ferments out without changing the flavor much and does so quickly.

In general, you’ll want to add about two or three gravity points of priming sugar per gallon of beer to prime it in the bottle. This ends up being about 3/4 cup of corn sugar or 2/3 cup of white sugar for a five-gallon batch. Boil that in two cups of water and let it cool before you add it to the beer.

To make thingsĀ even easier you can even get sugar tablets that allow you to skip the whole process of adding sugar to the beer before you bottle it. To use them, you’ll simply add beer to your bottles like normal and then slip a couple of tabs into the bottles before you cap them. Easy peasy. They are a little more expensive, but it’s cheap insurance against messing up the priming sugar!

Use better bottles or different caps

While the first three items on this list are by far the most important, you should also pay attention to the quality of the bottles and caps you are using to make sure they aren’t a weak point.

Many homebrewers reuse commercial beer bottle. That’s generally okay, but you’ll want to avoid trying to use twist offs (the cap will never seal properly) and visually inspect every bottle to make sure there aren’t any thin areas or other imperfections. As you continue to use the bottles over and over again, they can also get chipped.

Always be sure to buy new bottle caps – don’t try to reuse old ones!

Consider getting into kegging

This might sound like a lame solution, but making the jump to kegging is one sure-fire way to avoid bottle bombs – there won’t be any bottles to explode!

True enough, kegging wouldn’t fix an underlying issue with the beer such as an infection or a fermentation that hasn’t finished. It will at least be safer and easier to manage if there is a problem and it will eliminate the need to clean and sanitize dozens of bottles for a batch of homebrew.

The downside to kegging is that improper sanitation inside a keg could still lead to an infection but, instead of maybe impacting one bottle, it could take down the whole batch!

What to do with a batch of exploding or gushing homebrews

If you’ve already bottled up a batch of homebrew and experienced an exploding or gushing bottle, then you are probably a little scared and uncertain of what to do next. The good news is that just because one bottle went off doesn’t mean the whole batch is ruined! It could have just been one infected bottle or that a little extra priming sugar went into that particular one. Let’s assume that you’ve had a bottle explode without touching it and see what we can do to handle the situation.

An exploding beer bottle could cause injuries

Before you try anything, please understand that homebrew beer that explodes when opened can cause serious injuries. Flying glass shards are a very real, very dangerous thing. With that being said, taking the proper precautions should help reduce any serious risks while you are handling the bottles and determining whether or not the batch can be saved.

At the very least, please use:

  • Protective eyewear that fits flush to the face without gaps around the lens (no sunglasses!)
  • Better than eyewear is a full face mask (preferably one that covers your neck as well
  • Leather work gloves
  • Heavy jacket
  • A heavy towel or canvas bag to handle the bottles themselves

While this might seem like overkill, you’ll be happy you have it if a bottle explodes in your face!

Give them more time in the bottle

The simplest strategy is to not touch the bottles at all and simply leave them where they are to spend more time in the bottle. This is assuming they are in a place that will be safe if another bottle goes off. Ideally, you’ll have them in a box, cabinet, or some other storage area that is closed off, cool, and dark.

Using this method, you’ll know pretty soon whether or not you are going to have multiple bottle bombs on your hands because more will start exploding. Typically, exploding bottles caused by excess CO2 is not something that can be ‘fixed’ with extra time in the bottle, but at least you’ll know if the problem is getting worse or staying the same.

Testing the rest of the batch

If nothing else happens for a week or two, it’s probably safe to try to open a bottle and see what happens. Take a few bottles at random and wrap them up in your towel to take outside in a safe area. Open them one by one and observe the result.

There are a few possible outcomes:

  1. The bottles all open normally and don’t seem over-carbonated then you likely had an isolated bottle infection, or you didn’t mix the priming sugar well enough. Feel free to taste the beer to make sure it’s good…for science.
  2. If all of the bottles gush out and seem over-carbonated when you open them, then taste the beer. A sour or overly yeasty taste likely means that you have an infection and it’s likely the whole batch is bad.
  3. If all of the beers gush out, but they taste delicious, then you might just have a simple over-carbonation problem and not an infection. If that’s the case, move on to the next section because cooling the beer could fix the problem.

Cool down the whole batch in the fridge

Gases occupy more space at higher temperatures so an easy way to manage a batch of beer that is over-carbonated is to put it in the fridge to cool everything down. As the beer cools, the pressure inside the bottle will go down and you can reduce or eliminate the amount of beer gushing out of the bottle when you open it.

If you don’t have enough room for the whole batch, you can keep the warm ones in a safe place and put a group of test bottles in the fridge to see what happens. I would leave them in the fridge longer than you think you need to to get them cold (a day or two) just to be safe.

Crack one open.

If everything is normal and the beer tastes great – success! Have a homebrew!

If not, move on to dumping.

Get rid of the whole batch

If you’ve determined that your whole batch is infected or you simply can’t get the beer to stop gushing enough to enjoy them then you will probably have to resort to dumping the whole batch.

Suit up in your safety gear, bring the beer outside, and dump them one by one. Say a little prayer to the beer gods while you do it. Don’t worry, no one will judge you if you shed a few tears during this process.

Go inside, calm down, and have another homebrew!

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