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Guides Food Guides How to make a fermentation airlock for your Ball jar

How to make a fermentation airlock for your Ball jar Mattie

Written by Mattie    
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How to make an airlock for a Ball jar

Fermenting foods is a great, rewarding hobby but you have to be careful because one day you might wake up, look around the room and see multiple vats of vegetables bubbling away in various parts of your home. For a second, you'll wonder how this came to be. Maybe your girlfriend or roommate will just come clean with you and flat out ask "why there are so many things fermenting around the house?" and "I wanted to have people over tonight but I don't know if I can because the house smells kind of funny".

Do you have a problem with fermented foods addiction? Is the health of your gut direcly proportional to how funny your house smells? Well, it doesn't have to be that way because I'm going to show you how to make an airlock for all those random Ball jars you have so you'll be able to ferment more easily, with less funny smells to concern your housemates. An airlock is a system that puts a lock on air coming into your fermentation vessel so only the stuff that needs to get out, namely C02 can get out when it needs to. Other stuff like funny odors are kept at bay, safely around your fermenting food and out of the way of your housemates noses. This way you can ferment even more food and since they're in Ball jars that come in different sizes, you can hide them in random places around your house! Ok I was just kidding about that last part. You really need to cool it a little on this fermentation habit of yours.

Other advantages of an airlock:

  • You won't need to resort to using the dreaded cheesecloth desperately secured to the top of the fermentation crock with a rubber band. This is precisely what will make your house smell funny. What if the rubber band breaks and flies get in? Pandemonium and broken dreams. And how do you clean that thing? You do wash it don't you?
  • No more slime on the top of your vegetables. As your vegetables ferment, C02 is released as a byproduct. If oxygen is able to get to them, aerobic bacteria (bacteria that need oxygen in order to function) such as acetic bacteria start to grow. These bacteria produce slime, also known as biofilm, as a byproduct. Fermenting with an airlock allows the C02 to push out all of the oxygen in the container so it can't get back in and facilitate the acetic bacteria. Even if you were to secure the top of your fermentation container with an airtight cap and "burp" it every day to release C02 pressure, oxygen could get back in resulting in slime.
  • After you're done fermenting, you can just replace the airlock cap with a regular Ball jar lid, place the whole thing in the refrigerator and be done with it. Less moving ingredients around means less work for you and less risk of contamination.
  • It looks way cooler than wrapping a cheesecloth around a crock in desperation. Your friends will be impressed and want to be more like you. Your house will look like a freaking lab.
  • After you make a few airlocks for your Ball jars, you'll be able to easily screw them onto any size jar so you can ferment and pickle significantly more easily.
  • Since ball jars are labeled with millileters on the side, it'll be a cinch to calculate salt percentages for your brines on-the-fly.

There is however one disadvantage to using airlocks on Ball jars which is the reason why I still have at least one ceramic crock with a built in trough airlock kicking around:

  • Your sauerkraut and kimchi will need to be kept under the brine in order for it to be exposed to the proper salt level and ferment properly. Since there's really no easy way to weigh down your fermentables uniformly in a large Ball jar, you won't be able to make these sorts of ferments in these types of jars. You'll need to resort to a traditional crock that has ceramic weights, or a suitable large bucket with appropriate weights. But for things like fermented hot sauce, pickles, and other ferments will be fair game.

Learn how to make Wild Fermented Pickles

How to make an airlock that will fit on any wide mouth Ball jar

1) Buy plastic storage caps

Start out by purchasing some Ball Plastic Storage Caps for widemouth jars. I recommend the wide mouth jars because why not? Do you actually enjoy fishing fermented vegetables out of a narrow mouth jar? If you do, go for the plastic storage caps for regular jars. You'll get eight of these plastic storage caps. I ended up using half of them as actual lids to some of my Ball jars and the other half for modifying for my airlocks. This gives me four airlocks which is enough for now.

2) Get the right drill bit for your drill

If you don't already have one, get a ¾ inch drill bit for your drill. You do have a drill don't you? 

3) Get stoppers to allow airlocks to fit to your caps

Since we're borrowing this technology from the homebrewer world, we need to either hit up a homebrew supply shop or look to other online avenues to acquiring a bunch of size Number 2 drilled rubber stoppers.

4) Get your airlocks

Now we need the airlocks that will go into the stoppers. Pick up some S shaped airlocks online or at your local homebrew shop. There are several different airlock designs but I prefer this particular model because it holds lots of liquid and because it has smooth sides, it bubbles really quietly. This is a big deal because some of these airlocks are so loud, you could swear that the bubble monster is getting closer and closer, courting you while you're sleeping in the middle of the night.

Fermentation airlock parts

How to assemble your airlock

1) Drill a hole through each cap

Select as many plastic jar caps as you're going to need and drill a hole directly through the top of each one. 

2) Fit your airlocks into your stoppers

Press your airlocks through the hole in your drilled rubber stoppers. It's important to do this before you press the stoppers into the jar caps. If you're having trouble pressing the airlock into the drilled stopper hole, run the stopper and airlock under water which will slightly lubricate them and allow them to slide better.

3) Press the stopper into your cap hole

Now that you have your airlocks pressed into your stoppers, press them into the hole in your jar caps and viola. You can now use your Ball jars as fermentation jars.

Here's an example of how easy it is to calculate salt brine concentration with a Ball jar and a scale. You add enough water to make it up to the 1000 mL line of the half gallon Ball jar. Accounting for the fact that 10 grams of salt added to 1000 mL of water equals a 1 percent salt solution, add the appropriate amount of salt by weight. For example, 40 grams of salt added to 1000 mL of water equals a 4% salt solution. Now add your desired spices, place a watertight lid on and give it a shake to dissolve the salt. Place your vegetables into the solution, screw your airlock on and you're ready for business. 

Calculating salt brine concentration

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User comments

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There's actually an easier way to do this, using the metal lids. Use the same airlock, but then drill a 1/2" hole and a rubber grommet

I used to do this for small yeast starters.
Commented by Nat October 18, 2013

There's actually an easier way to do this, using the metal lids. Use the same airlock, but then drill a 1/2" hole and a rubber grommet

I used to do this for small yeast starters.

Owner's reply

Great find Nat! That's great to know these little grommets are available for fitting airlocks into lids as an alternative to the rubber stoppers. Thanks for letting me know!

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