Introduction: Poor Man's Airlock

Picture of Poor Man's Airlock

I have always been brewing in plastics bottles (not very professional, but for me it works without problems) and so I thought of some better way of getting CO2 out of the bottle and no oxygen in than capping the bottle and letting it squeeze when there's high pressure.
The liquid-filled airlocks are fine but making them is a horror and also, I was used to let bottles in cellar for long time until it's finished and sometimes I found out that it dried...
So there's one primitive airlock that needs no care.

It works just on two facts:
1)There's still higher pressure in the bottle than outside (this works until yeast dies or runs out of sugar)
2)Relative molecular weight of CO2 is 43.99 g/mol. Air has 25.93 g/mol. Result of this is when you have CO2 in bottle, it won't mix with air until wind blows into the bottle (at least for some time, due to diffusion).

Step 1: Materials

Picture of Materials

OK, now what will we need:

Step 2: Making the Base

Picture of Making the Base

First, take the sand paper.
If the cap has some imprint on it, sand it down so the cap is flat.
In the middle of the cap, use the sand paper and make it rough. It should not be smooth.

Now we will drill three holes so that an M3 screw can be put in them.
One will be in middle and the other on opposite sides, place them near the inner cap circle.
Now, rip off anything overlapping off the holes.

Step 3: Placing Screws

Picture of Placing Screws

Now, put M3 screws in the outter holes with head down.
From top, put pads on them and then nuts.
Tighten until screws get  partially inside the plastic (this will deform the plastic a bit).
This will ensure they will be air-tight.
Look at photos.

Step 4: Making Spring Holder and Placing Spring

Picture of Making Spring Holder and Placing Spring

Now, cut a piece of metal. The shape of it is up to you, but rectangle is easiest.
Its length should be about the same as cap's diameter.
Make it wide enough so it won't break when you make 3 holes into it.
Use rasp to make edges and corners round (for safety).

Now drill into it 2 holes of M3 size in the same distance as the screws are placed in cap.
Between them, make another hole. Its size will vary, because you need to use screw big enough to hold the spring.

Now, put a short screw in the middle hole.
Put pad and nut into the spring and screw it together with spring holder.
You can see it on photos.

Now just put the spring holder on screws and put nuts on them.

Step 5: Making the "valve"

Picture of Making the "valve"

Now, cut a rectangle out of rubber. It should be some rubber that doesn't bend very easily.
I used pipe sealing rubber.
Its width should be bigger than diameter of hole in cap.
Make it longer than its width.

Put some oil on the top of cap around the hole.
It should be some light oil with no smell, non-toxic. I would like to suggest you to use silicone oil.
(It is often sold as spray, very good for this use)
Put also a bit on the bottom of rubber.
Put the rubber between the hole and spring. It should cover the hole and spring should be applying some force onto it.

Use the nuts on screws to adjust the pressing force of spring.
It might be good to use some anti-corrosive or at least any protective paint on heads of the screws.
The rest which will not be inside the bottle doesn't need any paint, the silicone oil will be enough.

Good luck in brewing!


Nitr0 (author)2016-11-04

Grab a straw, make a hole in the lid, secure the straw with hot glue or even plasticine, and direct the end of the straw into a cup of water. Easier and cheaper than this.

AidleMohd (author)2012-03-29

Thanks for the idea

yoyology (author)2012-01-22

Great 'ible!

I make Ginger Ale at home in a 3L bottle, and this would be perfect for letting the gas out over the 3-day fermentation period.

CaseyCase (author)2011-07-30

You could use a balloon with a pinhole as another style of a poor man's airlock.

imajem (author)CaseyCase2011-08-04

What's the pinhole for?????
The balloon works great without it!!!

CaseyCase (author)imajem2011-08-04

Yeast eats the sugars and produces alcohol and carbon dioxide. If you did not release the pressure built up by the carbon dioxide in the bottle, it would eventually explode.

As an "airlock," the hole in the balloon allows excess carbon dioxide to escape.

dutado (author)CaseyCase2011-12-15

I use plastic bottles and I never came across any problem with it. No exploding bottles, no infection in wine. Just that several times I forgot the bottles closed and the yeast stopped working and living. (So far, the best ones are Sprite bottles, they have thick wall).

CaseyCase (author)dutado2011-12-16

I have read that plastic soda bottles can withstand up to 150 psi, so I imagine that the risk of bottle explosion in this situation is quite low indeed.

tharvey4 (author)2011-11-18

You can find these on amazon, 3 for $1.50, and they're real airlocks. Just putting that out there.

Ranie-K (author)2011-07-30

Here's how I do it (pierced balloon):

imajem (author)Ranie-K2011-08-04

Me too!!! Works great...............

Computothought (author)imajem2011-09-17

Me three.

Avatar_I_Am (author)2011-08-08

Dutado- Everyones' comments aside, I say you are pretty smart to make a pressure releif valve where non existed- at least in your immediate area!

Sure, WE can just get into the car, and drive to the nearest outdoor supply store, and pick one up, but can ANY of you do better with stuff you have on hand when YOU need a pressure releif valve?


I sat here and tried to think if I could make one, and I don't have the spring on hand...


nathangill (author)2011-07-30

A poor man's airlock indeed. The poor guy wasted all that time and hardware making it when there's a cheaper (if you don't already have your hardware) and less complicated DIY airlock -

Cut a hole in your lid
Stick some clear plastic hose into the hole, but not so far that it touches your liquid.
Stick the other end of the hose into a container of water that's lower than the top of your fermenting liquid.

Saved me plenty of times when I ran out of proper bubble airlocks (which are only $1.25 at most retailers)

Steelsmith1 (author)nathangill2011-08-04

I started making wine about48 years ago. The problem with the hose and water is that when the fermentation dies down and the barometric pressure changes the hose will suck contaminated water back into the wine. The commercial locks avoid that. I normally take a plastic grocery bag and put a piece of that either over the bottle with a light rubber band or in a bucket I put a trash bag over the bucket and a couple of turns of springy yarn. It has worked flawlessly for me EXCEPT when there were children, cats or puppies nearby who tore the plastic. I once saw a man who lived alone who made wine in jars and jugs. He put a flat piece of glass over the top and it worked well, but he was a recluse and lived alone.

merijnvw (author)Steelsmith12011-08-04

so you started making wine when you were -1 years old??

Steelsmith1 (author)merijnvw2011-08-04

That would be 14-15 years old, since I'm 63 now!

merijnvw (author)Steelsmith12011-08-08

then the age on your profile is incorrect: it says 47

bluenevus (author)Steelsmith12011-08-04

We do the same for brewing beer - a wide roll of plastic wrap (lunch wrap, Glad Wrap, cling film, Saran Wrap) does the trick without any problems. The rubber ring seal taken from the fermenter's lid works to keep the plastic wrap in place. You can be sure it's sterile too, so if it falls onto the wort, no contamination.

You should use vodka as your airlock liquid. The alcohol reduces the chance of contamination. The only problem I had was that it evaporates faster.

dutado (author)geezer.nelson2011-08-04

In chemistry, we use concentrated H2SO4.

dutado (author)nathangill2011-07-30

Yes, I've tried this also. Might work even better, but in our country thin hoses are not sold everywhere and if you find some at hardware shop, they are made of silicone - so you can't glue them to the cap.
And if you glue it, the smell of glue gets into your drink.
Also, I wanted something that can't be easily broken.

kludge000 (author)2011-08-06

Just priced a gas-lock that would fit 2 litter bottle. $1.50...

Spokehedz (author)2011-08-05

Nice job on the write up even though English is not your first language!

How I do it is to get a length of tube, and put it into a jug of water. Works great for me, but I will have to remember this if I get into a pinch in the future.

Beergnome (author)2011-08-04

use Stainless steel hardware through out, and the rubber should be food grade as well...
get some white lithium food grade machine grease for your "oil seal"

very nice instructrable!

dutado (author)Beergnome2011-08-05

I used silicone oil, because it doesn't stink and won't harm you if you swallow a bit of it. And as the oil covers whole surface of rubber, water won't get to it.

Beergnome (author)2011-08-04

full disclosure, I am a professional brewer... beer pays my bills...

so, with all that out of the way...

this is not a airlock, this is a pressure relief valve.

to those of you who have offerd advice on diffrent substances to use in an air lock, or larger blow off tubes to larger bucket type airlocks?

y'all done missed the point ;)

the author of the 'ible 'expressed concern over airlocks evaporating off when "long term projects" are left to condition unmolested.

the purpose of an airlock is to allow the tank to out gas, and not let any outside gas enter into the vessel that could cause contamination.

this device allows pressure to build up, then release when sufficient back pressure builds up. So, more of a poor mans safety release valve than an airlock.

if you REALLY wanna go "poor man" about it.. just stick a balloon over the neck of the fermentation bottle for the same effect ;)

often times when we got a tank of brew, like say our barely wine, needs to hold at cellar temp for a period of say.... six months.. once fermentation is done we'll stick a butterfly valve on the tanks blow off tube and seal it off. At that point if any latent CO2 pressure builds up in the tank, the safety relief valve will let off until the tank equalizes to it the safety zone.. an added benefit of this is that before the tank lets off, a lot of CO2 returns to suspension, so at finishing time, carbonation is a matter of a mild adjustment rather then a full blown forced carbonation.

dutado (author)Beergnome2011-08-05

OK, i made it mainly because I was too lazy to catch a bus, travel 15km and back for real airlock. This was an emergency solution.

greatpanda (author)2011-08-04

Excellent! I noticed you're in Czech Rep., it's probably difficult to locate "proper" airlocks there, and "food grade" probably just isn't available there, at least in the hardware store. I've had trouble occasionally with them drying out as well, especially with mead (honey wine). As a note, what you call "pads" are (at least in the US) called washers, the ones with ridges are called lock washers.

dutado (author)greatpanda2011-08-05

Thanks, I was using Google translator for words I didn't know.
Yes, it's a bit difficult to get airlocks. I know only of one shop which has them (also has yeast, yeast salt, K2S2O5,...).

torned00 (author)2011-08-05

whats this for?

techno guy (author)2011-08-04

Isn't this valve that you are using as an airlock commonly called a safety valve?

rockhardmj (author)techno guy2011-08-05

A check valve, I believe is what you are referring to, is the basic concept here.

Huzudra (author)2011-08-04

How about set a marble atop a rubber o-ring affixed to a small pinhole in the cap, use a bit of rigid tube to keep the marble from getting knocked off. More or less how I keep air from sucking back into my charcoal making buckets. Except I don't use an o-ring, just a dent with a hole at the bottom and a marble or heavy ball bearing.

menahunie (author)2011-08-04

here's how I do it and very very simple.
Go to a store that carries tire valve stems. Drill a hole in the cap and pop in the valve stem. You can release co2 by just pushing on the stem valve like you do to let the air out of a tire or use it to inject gas..

markbyounger (author)2011-08-04

I just sketched a cross section of this for myself and thought some of you might like a copy. Great instructable (it has solved a problem I had thought about before).

townsend1212 (author)2011-08-04

I'm looking at this and see potential for a suction cup to pick up glass or plastic sheets.

jumpfroggy (author)2011-08-04

Neat! As an alternative, what about those one-way check valves they use for car vacuum hoses? They're very small, and I don't know if they leak backwards over time. But they're cheap and may be available at car repair places. Worth a look, I suppose. Not sure what disadvantages it might have for this type of use.

sitearm (author)2011-08-04

@Dutado; Hi! I like this!

It's like the Soyuz Spacecraft of pressure caps: simple, strong, functional, reliable :)

Like @RobotLover, I was puzzled by the title, "Poor Man's Airlock." But when I saw the picture I HAD to investigae. And I have now learned more about making fermented beverages.

Nice! :)

eosha (author)2011-08-04

Nice! It's a homemade version of an Oztop (, which I've used to good effect for many years.

Oztops have the added advantage that they retain a certain pressure, so the product can be carbonated.

Robot Lover (author)2011-08-01

That's pretty cool. I got the twitter text message and was like WHAT! POORMAN AIRLOCK!! until I saw it was for brewing!

ynze (author)2011-08-01

Nice I'ble! I like it!

Kryptonite (author)2011-08-01

Nice photography, that first picture's incredibly clear for such a close - up shot.

dutado (author)Kryptonite2011-08-01

Nice to hear that my N5800 XM does good photos.
It could have been better if I used my camera.
If you want to shoot macros with mobile, put a convex lens in front of your sensor.

Kryptonite (author)dutado2011-08-01

Interesting, thanks!

dutado (author)2011-07-31

I have made another version - no cutting of metal

batonas (author)2011-07-30

use air baloon with a hole :D as simple as that
TIP: poke a hole with a small needle :D :D :D

dutado (author)batonas2011-07-30

Tried and didn't like it.
The drink gets a bit of smell and taste of rubber.

batonas (author)dutado2011-07-31

bicycle valve would also do the job I have used it for bottle rockets
if you would like to do it make a little smaler hole in the cap so that valve dont fit easily and push it in with great force

JKR (author)2011-07-30

Nice instructable; very detailed with clear discriptions.

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