How to make an Airlock Cap


This was the start of my first airlock cap attempt.

I new that I was not satisfied with our fermenting set up.  Not the antique 2 gallon crock nor the one gallon glass jar with glass lid.  The mold and scum, while expected, was not acceptable.  Internet research had turned up fermenting systems that used an airlock but I was unwilling to spend what they where asking.  So we set out to make our own airlock system.

I started by buying a half dozen, half gallon, wide mouth, Ball mason jars.   3capsThen I found a local beer making supply house that sold airlocks.   So my first airlocks where constructed using the standard wide mouth two piece canning lids,  a couple of varieties of airlocks and some tight fitting o-rings to seal the airlock to the lids.   I also used one piece metal lids saved from grocery store products that fit standard Ball canning jars.

From these first tries I found that the o-rings did not seal well enough by themselves.  And the 2 piece canning lids where not convenient to use during fermentation.   All the metal lids tended to develop rust spots after repeated usage.   And the one piece “S” shape airlocks where too difficult to clean.



That brings me to my present, and very acceptable, airlock cap system.   The o-rings have been replaced with 100% silicone sealant.   This needs to be food grade silicone,  no kitchen and bathroom silicones with mildewcides.   Most, easily found, aquarium 100% silicone sealants are food grade.  But check the ingredient list.


ballcapThen there was the rusty metal lids.  These have been replaced with plastic lids made by Ball.

They come in wide mouth and standard mouth sizes.  I found them at my local grocery store along with the other canning supplies for about $3 per box of 8 caps.   These are also very handy to use to cap the fermentation jars after they are done fermenting and need to be stored in the refrigerator.  If not found locally, they are available on EBay.

airlockAnd for the airlock itself, I have settled on the 3 piece design made by Buon Vino Mfg.- Canada.   It is inexpensive and the unit comes apart for cleaning.   These cylinder airlock units are carried by most beer and wine making supply stores.   I have also seen them for sale on EBay, just search for “airlock”.   Locally they cost me $1 each.




The actual construction of the cap system involves drilling a hole in the center of the plastic cap.  The three piece airlock shaft has a slight tapper, so the hole is sized such that the airlock fits snuggly when inserted to a depth of about half an inch.


A bead of silicone is then applied around the shaft both on top of the cap and then on the underside as well.   Wait a couple of days for the silicone to completely cure before using the cap.

And that is the airlock cap design I am presently using.

Future design changes:  grommetMy next version will incorporate a grommet seal instead of the silicone sealant.   I hadn’t already gone this route because of the cost of the grommets in small quantities and the fact that I could not find the correct size locally.   I’ll post pictures when that design change is made, but until then I’m satisfied with the performance of my current airlock caps.


Final design upgrade using rubber grommet.


 I just made my final design change incorporating a rubber grommet to hold and seal the air-lock into the plastic cap.  Picture shows completed design with an extra grommet on edge. 

Found an online site that sells them in small quantities for a reasonable price.

Love this design.


16 thoughts on “How to make an Airlock Cap”

  1. While I am not endorsing this company nor suggesting that it is the best choice for you, here is where I got my small quantity of grommets:
    6250 NW 27th Way
    Fort Lauderdale, FL 33309
    954 861-2000

    Item# OMAR-1787

  2. Do you mind sharing where you were able to buy the grommets? I see most places require a large minimum order. My husband is Korean and I’d love to try to make some of these so I can make some kimchi. Thanks!

  3. Thank you for this article. I am just starting to make fermented vegetables and although I love the idea of a traditional pickling crock, I think jars with air locks seems much safer and more practical.

  4. Thank you for the valuable info!
    I have a question, though. Do you want any airspace in the jar, or should it be full of liquid up to the brim and pushing up the airlock?

    1. No head space!
      After filling the jar as full as practical with the vegetable mater I weight it down with a glass slug to keep it submerged and away from the airlock. I have found antique jar glass lids, salt table cellars, etc work great. Anything that is heavy for it size, is food safe, and does not react to salt or acid.
      Then I fill the jar as full as possible with brine solution. Attach the airlock lid and add water to the airlock.
      Place the whole jar/airlock assembly into a bowl or pan to catch the fluid that will be ejected through the airlock as the mater ferments.
      By filling the jar completely full you starve the undesirable oxygen loving aerobic bacteria. And you maintain a low oxygen environment that is needed for the anaerobic lactic-acid bacteria.
      I find that after about 3 weeks, or when the veggies stop bubbling, it is ready to test (taste).
      Good luck.

  5. Hi, I came across your article when I was searching for a way to seal the Ball regular mouth plastic lids to the 4 oz glass jars I have. I am making baby food and freezing them directly without canning. But they dont seal well. So i was searching for orings but i have no idea how to find the right size and after i read your article about using a silicone sealant. Got me thinking if i can use the sealant to permenately put it on the inside rim of the lid? Do you think it’s ok if it touched the food?

    1. Hi Cynthia,
      I don’t know. I am suspect of most types of plastic and sealants. And prefer to have only glass or stainless steel touching my food. Of course, this is not always possible. Sometimes you just have to do the best you can, and maybe put up with a less than great seal. Keep turning over your inventory in the freezer.

      1. I too don’t support plastic use but when it comes to lids, there aren’t many options. I have seen a korean company making glass containers with a stainless steel top. I thought it was a great idea but the smallest size is way too big for single serving of baby food and ofcourse the high price tag $20 for a single container. I am looking to store a week’s worth of supply so that will not do.
        I think what I might end up doing is what I used to see my grandmother do when making jam. Put a piece of cloth before putting the lid on. Wish I asked her why she did that, wonder if cause the lids rusted or some other reason passed on through generations. That should prevent any contact of the lid with the food. Might help prevent spillage too.

        Appreciate the comments!

      2. This doesn’t address your question but… How old is your child? Have you thought of using a baby food mill so you can just grind up whatever you are eating at the time instead of making it ahead? OR better yet not feeding mush but rather feeding your child food he/she can pick up and eat himself/herself? Studies are showing that babies don’t need to eat solid food until they can, to some degree, feed themselves. Just something to think about.

    2. First, make sure you have “Food Grade” silicone sealant. As if the FDA know what they are doing. And make sure that it is completely dry and cured before you use the lid.
      What to put our food in is always a hard question, especially if it is for a child. I would also suggest that you NOT fill the jar completely to the top and freeze it when sitting vertical, so that the food does not contact the top or the sealant.

      1. Thanks Dan for the info on silicone seals. Wish they also sold one for the regular size jar caps. While a bit pricey, I will have to give them a try.

  6. Thank you so very very much. This is exactly what I was looking for ! I have health complications and so finding an economic answer for fermenting food is very important. You have saved me time and effort. You did a wonderful job of explaining. Thanks sincerely for sharing this.
    Best Regards,