How to make a fermentation airlock for your Ball jar, jug or bucket

How to make a fermentation airlock for your Ball jar, jug or bucket

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How to make an airlock for a Ball jar

Fermenting foods like sauerkrautkimchi, hot sauce, miso, yogurt and even spontaneous fermented beer is a great, rewarding hobby. What could possibly go wrong? One day you might wake up, look around the room and see multiple vats of ferments 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". Nice. It's all your fault. Your're now that creepy person with all the jars. It's kind of like being the cat lady.

Do you have a problem with fermented foods addiction? Is the health of your gut directly 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 and other containers 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; since it'll now be able to not only be in Ball jars, but other containers that come in a wider variety of sizes. You can hide them in random places around your house! Ok I was just kidding about that last part. Sort of. You really need to cool it a little on this fermentation habit of yours.

Lambic Beer Starter

Other advantages of an airlock are:
  • 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, the pressure buildup could turn into a dangerous situation.
  • After you're done fermenting, you can just replace the airlock cap with a regular 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 and other containers like food-grade plastic buckets, 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 milliliters 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:

In order to ferment properly, your sauerkraut and kimchi will need to be kept under the brine in order for it to be exposed to the proper salt level. Since it involves more effort to weigh down your fermentables uniformly in a large Ball jar, it's trickier to make these sorts of ferments in these types of jars. A reader in the comments of this article had a terrific suggestion to get around this: You can cut cucumbers to size and insert them vertically so they use the jar lid to push down the ingredients you're fermenting. That's definitely a viable option. But the easiest way is to resort to a traditional crock that has ceramic weights, or a suitable large bucket with appropriate weights.

If you're adding an airlock to the lid of a food-grade plastic bucket, simply purchase crock weights separately and now you'll have an affordable homemade crock. Easy!

Crock weights

Plastic bucket airlock

Learn how to make Wild Fermented Pickles.

How to make an airlock that will fit on any Ball jar or food-grade plastic bucket

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. 

If you're fermenting in a food-grade plastic bucket you can easily add an airlock to it. It's up to you whether you want to buy a separate lid just to use as an airlock lid.

2) Get the right drill bit for your drill

If you don't already have one, get a ½ inch drill bit for your drill. You do have a drill don't you? 

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

Grommets. These are what makes this magic possible. We're lucky enough to live in a world where some kind soul designed a grommet that allows an airlock to seamlessly fit into a ½ inch hole. This is a world I want to live in. I recommend ordering these online unless you're a fearless hardware store shopper. Technically, the're ⅜-Inch (9.5mm) Hole Grommets. They're made by a company called Gardner Bender and the part number is GHG-1538.

Fermentation airlock grommet

4) Get your airlocks

Now we need the airlocks that will go into the grommets. 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 or lid

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

2) Fit your grommet into the hole

Press the grommet into the hole you just drilled. It's important to do this before you push the airlocks into the grommets.

3) Press the airlock into your grommet

Press your airlocks through the grommet hole. It's a tight fit; if you're having trouble pressing it through, run the grommet and airlock under water which will slightly lubricate them and allow them to slide better. Congratulations! You can now use your Ball jar or food-grade plastic bucket as a fermenter!

Bonus: Find out how to calculate brine strength

Here's an example of how easy it is to calculate salt brine concentration with a Ball jar and a scale. First, 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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Food Grade?

I love this idea - it's a very neat solution. Just wondering if if matters if the grommet isn't food grade? It'll not bio-degrade over time and contaminate or anything?

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easy way to apply pressure on the inside of the mason jar

I love making kraut in mason jars and the trick to weighing down the kraut is actually to save the base of the cabbage, trim it to a little larger than the mouth of the jar, and after jamming as much kraut as you can in the jar, use the cabbage end as a plug. If cut to the proper size, the firmness of the cabbage will keep your kraut completely submerged until it's ready and since it's round, the downward pressure is pretty even.
Thanks for the airlock instructions :)

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