How To Make an Airlock Fit a Wide Mouthed Mason Jar

We’re a big fan of using airlocks for a lot of our fermenting.  They practically eliminate mold and make the entire process far easier and lower maintenance.

It was well over a year ago that we discovered an economical source for air locks that work with Mason Jars.   But there was a problem – the synthetic stops designed for brewing weren’t wide enough for a wide-mouth mason jar so we were restricted to using them in conventional mason jars.  Until this weekend:

How To Make an Airlock Fit a Wide Mouthed Mason Jar

I’ve never had a real need to use an airlock in a mason jar until this weekend.  The need arose when I realized I had almost 2 liters (approximately a half-gallon) of cabbage to turn into a kraut and I had a free super-sized mason jar.  These jars are scarce in the US but are abundant north of the border; they are almost 2 quarts (liters), wide-mouthed and perfect for my kraut.

The stoppers I use for fermenting in the ‘regular’ mas on jars are size 12 or 13.  While they are prefect for a regular mason jar, they fall into the wide-mouth jar and are useless.

Here’s how we solved our problem:How To Make an Airlock Fit a Wide Mouthed Mason Jar


  • 1 marker (a Sharpie works great for this)
  • 1 yogurt or sour cream lid (it’s sturdy and food safe)
  • a pair of scissors
  • A conventional rim for a mason jar
  • a rim for a wide-mouthed mason jar
  • other things not shown (though can be seen in top photo): 3 piece airlock with stopper, wide-mouthed mason jar and rim.


  1. Trace a the wide-mouthed seal on the top surface of the yogurt lid (that way the marker will not come in contact with your food).  Don’t worry about centering it – you’re cutting the edges out.  Note the distance of the marker lines from the actual lid – you’ll use the line as a guide but need to cut it smaller or it won’t fit in the rim.
  2. Trace the conventional rim to make a circle within the circle.  It doesn’t have to be perfect as long as there’s room for the ring to screw on (over the first cut).
  3. Optional step: hold a ring over the first circle to get an idea of how much you need to cut off.
  4. Cut the outside circle, staying within the lines.  You don’t have to be perfect but the goal is to leave enough plastic that the rim will be in 100% contact with the ring when screwed in place.
  5. Optional step: hold the rubber stop over the inside marker line to get an idea of how much to cut off.
  6. Slit the center of the yogurt lid with a pairing knife or your scissors.  Use scissors do cut the middle section out (I do this by starting small and cutting a larger circular pattern until I reach the outside.
  7. You now have your conversion ring!  Test it by inserting the rubber stopper into place (with the marker from the lid facing the wide end).  Assuming you are happy with the contact, place the airlock in place, fill with water as directed and place on jar before securing with a jar ring.

If you look carefully at the picture at the top you’ll see a bit of the yogurt tub and my marker line peaking through the gap between the jar ring and the stopper.


  • As long as you’ve cut fairly accurately, there will be 100% contact with the stopper.  It has some natural give that will allow uneven cuts to be embraced by the cork.
  • You could also use the inside of the ring to trace for your circle and then cut outside the lines.  This would be more precise but more risky as it could lead to irreversible error (the method described in the post could result in a ring that is too large and you’d trim material but this new method would yield the potentially opposite problem).
  • You can also use the bottom of the yogurt container; it tends to be thicker and could make a stringer lid.
  • The resulting seal will not be as strong as the stopper alone.  Escaping air and gas will escape from the easiest route which should be the airlock but there is the potential that it could escape in small gaps between the plastic and the stopper.  You’ll know this happens if mold appears and, like all fermentation, it’s perfectly acceptable to scrape this off the day it appears and continue.

Do you have any tricks for fermenting with air locks?


  1. I use a zip top bag as a fermentation lock as described in the book, The Joy of Pickling by Linda Zeidrich. Basically, you shove a gallon bag on top of your ferment and fill it partially with brine (not water, in case there are any leaks the ferment would not be diluted) and zip it closed. The bag acts as a lock by weighing down the contents of the ferment and because it is flexible you can push it down to remove air bubbles and remove it and clean it of mold does start to form.

  2. great post — I’ve been brainstorming how to do this, too. I buy those jars at Michaels (craft store).

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