Airlocks... A necessary evil.

When people get into home brewing, craft brewing or hand made beer - what ever you would like to call it - the one piece of equipment that gets the most attention is the humble airlock.

After all - it's the only visible sign to someone new to brewing that something is actually happening in the fermenter.

If you haven't taken the steps into brewing, I had better explain what it is, what it does and what goes wrong.


Basically, it's an 'S' shaped tube that is inserted into the lid of your fermenter. It has two fat bits at the top and the bottom of the 'S' and narrow tube in between. Sterile water (or similar) goes in the fat bits.

Pic of an airlock in action.

It sole purpose in life is to keep nasties out of your brew while venting carbon dioxide and other brewing gases from the fermenter.

The kinds of things it's designed to keep out are airborne pathogens - wild yeast, bacterial, etc as well as dust, bugs, etc.

Carbon dioxide is one of the major by products of fermentation. There are some other gaseous by-products, but they are inconsequential at this level. All excess gas needs to be vented else the fermenter would pressurise and perhaps rupture, spraying beery sticky goodness all over the room in which the fermenter sits. So, when the gas is coming out, the water lets it out and makes a delightful bubbling or blopping sound.


What goes wrong is actually pretty simple. There is not a whole lot to go wrong. No moving parts. No magic. Medieval technology. It's a tube with water in it.

What people perceive to be 'wrong' is that there is no airlock activity. No bubbling, no noise - nothing. It's not actually a defect: it means the gas is getting out somewhere else. in the same way that 'nature abhors a vacuum' and 'electrons follow the easiest path' so does CO2 being vented from a fermenter - it will take the easiest way out: A leak.

The usual suspects for leaks are the o-ring (if you have an o-ringed carboy or similar style fermenting vessel) and the grommet through which the airlock is installed.

If your fermentation has already started (i.e. you have pitched the yeast), then leave it alone and mess around with it when you're cleaning before the next brew. Taking the lid off unnecessarily is an invitation to infect the brew and make it not fit for drinking. What you can do at this time is investigate a little to see where the leak is.

The simplest investigation is to see if the airlock grommet is leaking. Boil and cool some water - about 100 mls is more than enough. Pour a little around the airlock grommet on top of the lid. If there is gas escaping, you will see some bubbles. You've found your leak! I'll tell you two ways to fix it in just a moment. Don't be tempted to use the old trick for finding gas leaks using soapy water. If it makes its way into the brew, you may well stuff the brew.


After this brew has finished and you're cleaning the fermenter, you can check the o-ring. Before we get to that, remember - the way to check that the brew is finished and fermentation is complete is that you have a matching Specific Gravity reading (which becomes your Final Gravity or FG) on two or more consecutive days.

After bottling or kegging (Why the hell are you reading this if you're kegging? You're already experienced!) and disassembling the fermenter and cleaning it to make ready for the next batch, check the o-ring. Look for kinks, breaks, big scratches or something contaminating the surface. Check the groove it fits into in the lid for the same defects. Finally, check the lip of the fermenter which the o-ring mates for the same defects, including roughness around the moulding seams. If you spot any defects here, rectify those.

When you next are installing the lid, make the o-ring a little wet with some boiled and cooled water. It will aid in spinning the lid down tight and giving a good gas tight seal. You don't need to screw it in super tight like a sexually frustrated silver back gorilla. A good firm seal is quite adequate. It's easier to screw the lid on too tight than it is to unscrew it.

If you want to get fancy-schmansy about it, you can get some food grade lube and lubricate the o-ring before installing it into its groove and also wipe a little along the sealing face of the fermenter's lip. All very professional, but needless expense and extra things to clean even more thoroughly each batch. Recommended only for gluttons for punishment.


Now - on to fixing that airlock grommet leak!

There are three main things that can go wrong:
[1] The grommet is damaged or worn
[2] The grommet hole is too big or not a good fit
[3] The airlock's tube doesn't fit well with the grommet.

If the grommet is damaged, replace it. It's about fifty cents. It's worth keeping a spare grommet and a spare o-ring in case you have a disaster on brew day and your local home brew shop (LHBS) is closed - like mine is on Sundays.

Otherwise, improving the fit of the airlock and grommet to each other needs to be attended to. The easiest way is to use some teflon plumber's tape to increase the girth of the airlock. Wrap a few layers aound the part of the tube which goes into the airlock. Make a smooth job of it so that it can slide into the grommet easily but with a bit of resistance. This will give it a tighter fit in the grommet, at the same time forcing the grommet to fit the hole more tightly.

Detail pic of a teflon wrapped airlock.

So, overall, the airlock is a necessary evil and a source of needless worry for new members of the brewing world.


Please, remember - don't go to brewing forums and cry about 'my airlock isn't bubbling'. You will be told to 'RDWHAHB' (relax, don't worry and have a home brew) - which frankly a bit insensitive because that's what you want to be doing a few weeks after starting brewing. So instead, sit back, have a crap commercial and be patient for thine brew will be the sweet nectar of the gods.

Cheers!!