This is another one of those questions that comes up quite often on homebrewing subreddits and forums. New brewers see flies, ants, and other bugs getting into the airlock and start to become concerned. But is it really an issue? If there are flies or other bugs in your airlock, is your homebrew fine?

If fruit flies (or other bugs) are in your airlock, your beer, mead, or wine is perfectly safe. The airlock is doing its job and protecting your batch. 

If you find flies or other bugs in your batch, that’s an issue – but if they’re just in the airlock, you have nothing to worry about.

In fact, flies and other critters getting into your airlock is not only safe, it’s expected! The flies are going to try and get in – the airlock simply them!

It’s the same concept as any other vessel. Would you worry about food in your pantry if flies or other insects were found on the lid of its container? Probably not! The lid is there to keep pests out.

Obviously, you can’t use a regular lid to completely seal up a vessel during active fermentation – it would explode from pressure! The airlock exists to basically seal off the vessel from the outside world, while letting that pressure escape.

So flies and such will get into it, the same as they’d get on the lid of any other sealed container. But the airlock is actively keeping them out of your beer, mead, or wine!

Why Are There Flies in Your Airlock?

Flies, and bugs in general, want your wort or must. It’s a great source of food! If you did not have an airlock, blowoff tube, or at least a bit of cheesecloth to protect your batch, you’d likely find a whole swarm of insects swimming in it!

And as fermentation occurs, gasses like CO₂ are being pushed out from the vessel through the airlock – carrying an abundance of scents and smells along with it.

Of course, these scents and smells attract insects, who try to get to the food source within the vessel.

Airlocks are not sealed! This is a fundamental part of their design, and it’s the reason we use them. The airlock creates what is effectively a one-way seal within the vessel, but in order to release CO₂ and prevent pressure build up, the airlock itself must remain open to the outside air.

And, of course, flies and other bugs can get into that open side.

However, they cannot get through to the other side!

Flies and other insects might be able to get into the airlock in search of the fermenting wort or must on the other side, but they will struggle to make it through the airlock liquid against external pressure, and will drown in the process.

This is the airlock working as intended!

However, it does mean you’ll often find a buildup of dead bugs in your airlock.

Can Flies Damage Your Beer, Mead, or Wine?

If you actually find flies or insects of any kind floating around inside the vessel – directly in your beer, mead, or wine and not solely in the airlock – then you may have cause for concern.

Flies and other insects are very unsanitary – they carry an abundance of bacteria and other spoilage organisms on their bodies. Flies literally crawl around on garbage and feces!

Granted, a fermented beverage is a hostile place for most spoilage organisms – the batch isn’t likely to spoil, although if you are concerned about anything, you should be on the lookout for a mold infection.

(I previously wrote an entire article on why you shouldn’t worry about botulism in your homebrew – the same concept applies to most other bacterial infections and spoilage concerns as well)

However, the insects can introduce other undesirable contaminants, such as wild yeast and souring bacteria. While this is not dangerous, it can result in unexpected changes to the flavor of your batch – and it might not taste great.

Additionally, the dead bodies of the flies and other insects will decay, especially if they’ve been sitting in the liquid for an extended rest or aging period. They will leak bodily fluids and other nasty things into your batch, which at a minimum may disgust you, and could potentially affect the flavor negatively.

If you find a bunch of flies or other insects in your batch, no one would judge you for tossing it. However, do realize that it doesn’t mean the batch is unsafe for consumption! If it doesn’t smell or taste bad, you can go ahead and drink it anyways.

Remember: I’m only talking about if it’s IN your batch! If the insects are just in the airlock, nothing in this section applies – your batch is perfectly fine and unaffected!

How to Prevent Flies From Getting In the Airlock

There is no way to 100% prevent flies and other insects from getting into your airlock. However, by replacing the water in your airlock with Star-San or a cheap high-proof liquor such as vodka, you can repel flies and dramatically reduce the number of them that get in there.

The liquor or Star San has a very aggressive smell, which overpowers any of the smells of fermentation that bubble up out of the airlock. This method doesn’t actually do anything extra to keep the bugs out – it just makes the airlock much less attractive, so they don’t try to get into it in the first place.

Personally, I always use cheap vodka in my airlock – and ever since making this change many years ago, I honestly have not seen a single fly, ant, or anything else in my airlocks since.

I have read reports that Star San is less effective at keeping away flies – although it’s my first choice for blowoff tube liquid, due to extra volume necessary, and I haven’t had any issues.

I’ve also read that darker liquors like whiskey can still attract flies. This doesn’t seem likely to me, but I haven’t actually used anything except vodka, so I can’t tell you for sure.

My personal recommendation: just keep the cheapest vodka you can find around, and use that solely for airlock liquid. You may never have to deal with flies in your airlock again!

Conclusion

Finding flies and other insects in your airlock is not a problem.

Honestly, you just shouldn’t worry about finding bugs in your airlock. If you ever see them in there, it should actually make you feel relieved: the airlock is doing its job and protecting your beer, mead, or wine from those pesky bugs!

If you want to do something about it, you can always just use Star San or cheap vodka as airlock liquid instead of water. It will repel them a bit, and you’ll see fewer insects in your airlock – it might even solve the problem altogether.