Fermenting in a Fido?

I want to address this topic because I get asked about Fidos a lot.  Specifically if it’s ok to ferment in them.  For those of you who don’t know what I’m referring to, a Fido (pronounced feed-o, it is Italian and not a dog) is an Italian made glass wire bale jars that are certified hermetically sealed.  That means, if the lid is closed, outside air will not come in.  They are excellent for keeping oxygen out of your ferments while in storage (they are also great for keep dehydrated foods fresh).  The Pickl-it jar that you hear me talk about is crafted from a Fido jar and many people have been fermenting in Fido jars recently.

This is a Fido with no airlock. Some have clear lids and some have blue lids.

I haven’t really talked about this issue until now simply because I do not know.  I am not ashamed to admit when I do not know something nor am I ashamed to retract when I find out I’m wrong (hello, I used to tell people to loosely cover their mason jar ferments and scrape the mold off). I have heard accounts of Fido jars exploding though I have not seen it myself.  I know of more than a few people who have “successfully” fermented many things for a few months now (I use quotations because by successful, I mean no exploding jars). But just last week Jennifer from Hybrid Rasta Mama had a lid blow off of a fido during a second ferment of water kefir.  She wrote about it here:   Exploding Fidos and Grolsch Bottles Gone Wild.  Some ferments are more active than others depending on ingredients and the temperature of the house.  If the gasses build up too fast, I can see how a jar can explode.

I admit, I’ve tried a few ferments myself because I had no open Pickl-it’s and didn’t want food to go to waste.  Plus I was curious how they would hold up.  I put them in a box in a closet to contain any explosions should they happen.  So far so good.

The ferments I have done in a Fido have turned out quite wonderful.  They are tasty, with no signs of oxidation and they have a wonderful carbonated fizz to them.  Nothing cooler than biting into a pickle that fizzes in your mouth.  Awesome!

So why haven’t I been shouting this from the rooftops?  Because there is more to fermentation than taste, presence of LABs and lack of oxidation (though those 3 things are very very good to have).  Here is the thing, a Fido lid latches on pretty strong.  That’s a good thing when we’re wanting to keep oxygen out but for escaping air it’s not a good thing.  While Fido’s will release air if enough pressure builds up (I’ve see it myself), it takes quite a lot of pressure before it does release.  I’d love to know how much exactly but again, not sure.  I’m guessing that pressure might be different from jar to jar as well.  Some of my Fidos latch harder than others so I imagine the tighter jars can hold in more build up fermentation gasses.

The bottom line is, I have no idea the effect CO2 build up has on the ferments and I’ve been reading plenty of studies that suggest it might be harmful.  I’m not talking harmful as if you’ll get sick and die if you do it.  I’m talking harmful as in too much CO2 might make a less than awesome probiotic power food and for those with serious gut issues, it might be a problem.  I’m not going to go into too much detail here about why it might be bad because… I’m not 100% sure at this point.  Still wading through research.

‘What I am sure of is the Pickl-it and the Harsch crock work which is why those are the only two systems I do recommend.  I’m not going to recommend something that I am unsure of.  Those two systems are anaerobic and they allow for off gassing with ease.

That being said, if Pickl-it’s are out of your price range, I would rather see someone use a Fido for fermentation than a mason jar.  Remember “good, better, best”?  I’m not sure where a Fido lies on that scale but I’m fairly certain it is much better than a mason jar.  So while you are fermenting in your Fidos, I’d still recommend you save up for a few Pickl-it’s, especially if gut healing is your main goal in fermenting until we know for sure whether a Fido creates as awesome of a ferment as a Pickl-it does.  And please, even though you may not have had a jar explode, lift the lever on your jars at least once a day.  Just enough to let air out.  Better safe than sorry.

And now I’m going to let you in on a little secret.  Bloggers make money from recommending products. *Gasp*  I know!  It’s horrible that someone should make money from their hard work.  Anyway, I digress.  My point here is not that making money for referring products is bad, but rather it is not the motivation for me to recommend a product.  I do make some money (not a lot) from recommending products I love.  But money is not what causes me to recommend or not recommend a product. If you click on one of my Fido links, you will go to Sur la Table where I will make a commission if you choose to by a Fido (thank you if you do!).  If you click on one of my Pickl-it links you will go to the Pickl-it site where I will NOT make a commission if you choose to purchase a Pickl-it.  Many other air-lock systems offer affiliate accounts as well and I’m sure if I stood behind any one of them, I’d make a nice tidy sum.  But I don’t believe in them.

That’s how strongly I feel about not recommending products I’m not sure of.  You can be assured, I will not recommend a product that I do not believe in fully and that I do not use myself.  And I will recommend a product I believe it and love whether I make a commission or not.

**This post may contain affiliate links. Purchasing from these links helps support Pickle Me Too, allowing me to post and store all of my free recipes. Thank you!**

46 comments to Fermenting in a Fido?

  • […] Melanie also shares her thoughts on fermenting in Fido jars in this post: Fermenting in a Fido? […]

  • This was a great post! Thank you for your courage to be honest.

    I just wanted to point out, though, that if you are unsure about the CO2 factor, then why fallback to “I recommend PI because I am sure it works?” This isn’t a criticism, so don’t take it wrong 🙂 But it sounds as if you have had success with BOTH a Fido and a PI. There is the same chance CO2 could be beneficial than harmful.

    It is possible excess CO2 might be harmful, generally speaking (although I’ve yet to find that in my research), but you’d never get to that high a level in a Fido. There is research showing that CO2 is actually helpful in a ferment – I believe I’ve provided you with those thinks. It can be confusing because the amounts aren’t generally specified. I don’t believe it is possible to get “excessive” amounts of CO2 in a ferment due to the Fido’s ability to release pressure.

    And it really doesn’t take much pressure before it is released. More than a water-filled airlock, yes, but not dramatically more. Not to the point of being harmful.

    Thanks again for sharing and being honest 🙂

    • Melanie

      Different jars seem to hold tighter than others as well. Just as an example, I opened a jar of squash relish this morning that I had transferred to a Fido thinking it had slowed down fermentation enough. I was surprised with there was enough force to throw the lid open and it had quite a bubble party. I honestly just don’t know the effect that much build up of gases has on a ferment. It’s enough to carbonate the whole jar. I just don’t know enough about it to feel comfortable recommending Fidos for fermentation.

  • Jennifer

    I think it is important not to dramatize the “exploding fido” concept. Newbies might take that to mean the glass broke – a scary enough visual to make anyone swear never to ferment in a fido. The lid blew off and the contents erupted with a lot of force, and a flying glass lid is certainly a hazard, but if you keep them in the closet, it is safer on the off chance that this happens. Fido fermentation has made it possible for me to afford to make awesome ferments.

    • Melanie

      Dramatizing explosions? I’d rather be safe than sorry. I’ve cleaned up plenty of glass explosions to know how serious they can be. We were lucky no one was in the room when they exploded because glass flew everywhere. If Jennifer had gotten to the lid seconds before it blew, the chance of it hitting her in the face are pretty darn high. I wouldn’t want to get hit in the face with that. I’m just saying if you’re going to ferment in something that does have the potential to blow, put it in a box or cooler to contain it. I for one would appreciate someone warning me.

      • Tanya

        Well I appreciate the information, as I am a “newbie”. In fact I have not even fermented anything yet. If us “newbies” click the link you provided about the explosion (lol – what a mess) and used some common sense, research etc. then there’s no reason to be turned off. It’s called using your brain.. not dramatizing.

        Thanks for all your work Melanie. This newbie (well actually I’m a not-even-startie) is still saving for pickl-its.

  • Sarah M

    Could you share with us the studies you’ve found which suggest CO2 is harmful to ferments?

  • I think fair warning of exploding jars is essential and it should make newbies wary of fermenting in a jar that is not set up to release CO2 and other fermenting gases as they need need to escape…

    I would be upset as a newbie to find myself in that situation without warning. Thanks Melanie for sharing that information!

    If you look at our ancestors did you will discover that this may be why porous crocks that could off gas as needed into the earth were favored – as we try to find a modern technique to recapture that ability to ferment and preserve – it’s important to try to replicate that off gas method…it’s not just CO2 that builds to the point where there is excess that need to be released….that’s why I prefer the ease of mind of fermenting in the Pickl-it. I would be happy to recommend or use another system as soon as I find one as good 🙂

    Fido jars don’t fit the bill for me – and with kids around – I can’t afford to take chances with explosions…but each individual needs to find what works best for them….

  • Melanie, thanks for a thought-provoking post. I take this as a little hint that there are a couple of potential issues with fermenting in a plain-Jane fido and that if those issues are of concern to me, I should do a bit more research on my own. In other words, “It’s a thing.” Much appreciated!

    I would much rather be informed that there are issues on the table than not. If I should ultimately choose to discount those concerns in favor of short-term thriftiness, that’s up to me. So far that is not my choice. I’m at a point where it’s worthwile to me to stack the odds in my favor health-wise to the best of my ability. For the past few months I have been using the airlock-modified vessels (pickl its) and so far am delighted with the results.

  • […] Without a Separate Airlock Part1.  She answers a lot of questions I had in my post from last week: Fermenting in a Fido? Share this: September 28th, 2012 | Category: articles, Fermentation Friday, […]

  • Connie

    Melanie, I would like to respond to someone’s post on your site but don’t want to unless you decide to allow it. So my question is — do you screen your posts? Feel free to email me rather than responding here and I’d give you more details and would alter what I do based upon your response.

    I LOVE your articles! I LUV your attitude and honesty! Thank you!


  • I think it’s important to mention this important fact: high sugar content ferments need an airlock. Period. That’s why wine and beer brewers use them in all ferments and you can buy them so readily at brew shops and winemaking supply stores. I would never take lightly the fermentation of water kefir or homemade soda pop, but I have no qualms about fermenting low sugar pickles and sauerkraut. The difference is not necessarily how MUCH C02 is produced, but how QUICKLY. In an average low sugar ferment, the gas is produced at a rate that allows the jar to offgas the excess safely. In a high sugar ferment, the gas is produced so quickly that slowly offgassing as it is designed to do just simply can’t keep up. Too much pressure builds and Wham! Explosion.

  • Tamara

    Just a quick note — if you’re already using Fidos and want to convert to Pickl-its, the Pickl-It people will sell you lid kits. It’s not on their website, but if you email them, you can get the Pickl-it lid kits and the Dunk’Rs (which I really wanted). It’s a better deal than having to completely replace your jars:

  • Steven

    I purchased very inexpensive fidos at my local Home Goods. I’m new to fermentation. I have brussel sprouts from my garden to ferment and will do so in one of the fidos mentioned above.

  • John

    I was excited about fermenting in a regular Fido w/o an airlock. Not mentioning any names, I emailed a company that sells fermenters/crocks about the safety of fermenting in a regular Fido. Below is their response. is there any truth to this or are they using scare tactics to promote their product?

    Regular Fido jars don’t work. You retain the oxygen in the jar which oxidizes the food. We’ve received quite a few calls from people who have had their Fido jars blow up. It only takes a shard of glass, embedded in walls or kitchen cabinets, to convince them that an airlock is absolutely necessary.

    With a regular Fido, are you going to be able to measure the oxygen? Or measure the loss of the strict anaerobic bacteria that you’re killing off with the atmospheric oxygen? How about measuring the amount of H202 you’re creating? Oxygen actives the production of H202. That’s why people who use the mason jar think they’re creating a very yummy batch of active food when the brine gets all nice and bubbly and burps up and over the rim of the jar. In reality, they’re only creating H202 which is killing off their probiotics. And when you get that much H202, you’re creating a big old batch of toxic aldehydes which thrive in those conditions. And your liver can’t break those down. That’s why some children are now presenting with a toxic liver, as if they’re an active alcoholic…………

    • Thanks for sharing that, John. I’ve heard much of the same here too. Enough cause for concern that I don’t recommend fermenting in a fido. Big bummer because that sure would be nice. They are still super awesome for storing ferments once the active fermentation slows down.

    • Marie

      I know this is an old thread but have to respond to this … This sounds like a TOTAL scare tactic, selective manipulation of facts and everything. LAB PRODUCE H2O2! I learned all about this in researching vaginal health issues. THE REASON we want LAB colonizing this area of our bodies is that they produce H2O2 which then kills off the pathogenic microbes on a daily basis … but DOES NOT kill the probiotic microbes! (why would LAB produce H2O2 that is going to kill their own colonies?) The H2O2 in ferments I would think would be a very good sign that LAB were active and happy. Raw milk also naturally contains a form of H2O2, lactoperoxidase, which also kills off pathogenic microbes but DOES NOT kill off the probiotic microbes.

  • John


    Do you have a sour pickle recipe?


  • John

    Forget it, just noticed your recipe link above. Sorry!

  • […] is another method I have mixed feelings about.  You can read my thoughts here: Fermenting in Fidos.  Basically, I’m unsure of the affect the trapped gasses have on a ferment.  It’s […]

  • BB

    Dear Friends,
    I’m a big fan of Sally Fallon’s “Nourishing Traditions” and did get up the nerve to cultivate sour cream on my counter top. It was delicious! But I still have serious reservations about food poisoning and have been cured of yeast growing in my blood stream (I watched it multiply in a microscope at the doctor’s office) and other bodily tissues. So I researched all the information on the ‘net I could about safety, procedures, equipment, etc. I also looked at Amazon reviews over the equipment suggested. There does seem to be a lot of conflict over equipment and rather than shell out precious finances for experimental products, I decided to think outside the jar. Here’s what I thought I’d try:
    1 large clear plastic box (with lid) three inches deeper than the tallest jar to be used.
    1 bag dry ice.
    1 small freeze proof container to hold dry ice in large box.
    6 mason jars or a number that will fit in the plastic box comfortably.
    Food grade dehydrating mesh to keep the food under the surface of the liquid
    Unflavored whey for inoculating food product (I like to get to the point of all this quickly)
    1 roll saran wrap
    Enough rubber bands for the jars
    Box of matches
    First load the box with filled jars covered with saran wrap and rubber band lids. Then load the box with carbon dioxide (remember the dry ice? It doesn’t take much, just put it the small jar or bowl in the bottom of the box). After the box is full of CO2, light a match and verify the level of CO2 covering the jars. The match will quickly go out at the CO2 level. Carefully cover the box and let it sit. Do a lit match check periodically and refill with CO2 if necessary, but not likely. The idea is the jars can outgas easily, no explosions and only CO2 is available to backdraft into the jars. The outgas will float out of the box, or at least above the CO2. If this doesn’t provide an anaerobic environment, I don’t think anything will. When the product is finished, take it out of the box and refrigerate. If I’m wrong, please enlighten me before I go out and buy the items on the parts list 🙂

    • Honestly that just sounds like way to much effort for something that isn’t too hard. A good jar with an airlock is all you need.

      Unless the plastic box is airtight, oxygen will still leak in.

    • Jeanmarie

      I agree, that sounds like way too much trouble. And why are you trying to re-invent the wheel when you haven’t tried the tried-and-true traditional methods of wild fermentation? I’m not convinced that Pickl-Its are the only way to go, or that Fido jars are problematic, or that Mason jars don’t work. I’ve used my Harsch crock, Fido jars, Mason jars with and without airlocks, and they all work. I prefer Mason jars with airlocks, and I’m still experimenting with Fido jars. Lots of people on the Facebook Wild Fermentation group attest to their success using Fido jars. I don’t like all this fear-mongering among people trying to promote a particular product line. This is old tech. Nothing wrong with new tech — I’d love to try Pickl-Its myself — but I’ve heard from people who claim inferior results, including mold issues, with Pickl-Its. There are other brands that offer essentially the same thing, as well.

  • I think one of the jars I bought when I first started is a fido. I use it without the rubber or plastic band that came with it. The glass top sits flush on top to keep any critters out, but loose enough that it can’t explode. But I do get… what’s that yeast film called? However, the salt can really corrode the metal part.

  • I am a fido wholesale direct importer and dealer…. For over 30 years… The usage described is NOT a recommended usage without venting. The jar is NOT made for self venting by stretching the lid with pressure.

    This warning was removed by another blogger on her site. … She thinks I am in “collusion” with a company that uses the vent system…. Instead of realizing I am just warning people that they are using it in a way not intended. Yes, many have success but is it worth the off chance of injury?

    Yes… Build up enough pressure and a jar can explode…. That is a fact.

  • […] on the blog last week from someone “in the know”.  My blog post where I question the safety of fermenting in Fido‘s received this […]

  • Hilde S.

    Hi Melanie!
    I love your website and all the great info on fermentation! I just wanted to pass on a note to you that you can purchase “D rings” for the fido type jars (made in Italy) from a company that is selling “pickl it” like jars called They also sell other individual parts such as “drilled” lids with airlocks for fido jars. You can take your regular fido jars, add these lids and you’ve got a fermentation vessel.

  • For anyone concerned with the exploding issue, I have a fix that eliminates this and makes the Fido jars 100% safe. It’s super easy…all you do is remove the bailing wire from the top lid and on both ends bend the wire down a little bit with pliers so the lid doesnt clamp as hard and creates a less tight seal. I adjust mine to where when I fill the jar with water and turn it upside down, if i tug on the lid water starts dripping out but when I stop pulling it seals and does not leak water. This simple adjustment also works with the swing top bottles so no more worrying if the bottle will explode. However, if you loosen the seal too much your drink will not have as much carbonation and be less fizzy so it’s a matter of fine tuning the adjustment to the level you feel comfortable with. Less seal= less fizzy, more safety. More seal=more fizzy, less safety.

  • Melanie, another thing with the Fido exploding safety fix I mentioned is that it also solves your concern with excessive co2 build up, and in essence makes the Fido perform identical to the Pickl-it. Using the technique I described in my previous comment, you can adjust the Fido lid seal all the way to the point that it leaks and does not hold pressure at all if you like. The pickl-it system does maintain co2 pressure, it’s just very low. Co2 is heavier than air so there will be a continuos layer of co2 above the brine. It will build up until the pressure is enough to force c02, and any oxygen above it, through the water and out through the air lock. By adjusting the Fido lid bailing wire you can get the seal to the point that it releases excess co2 pressure at a similar pressure it would take to force c02 through the water air lock and thus give you the same results as the pickl-it system.

  • I would be concerned about losing the hermetic quality of the fido using that “fix.” If air can get out, can’t it also get in?

    • No air can’t get in, unless the the jar has vacuum inside to suck it in, which is doesn’t. The fermenting process causes co2 pressure to build up. The inside of the jar will always be under pressure until you open the lid. The seal of the Fido jars from the factory varies from jar to jar. Some seal just right, and some seal too tight and create a risk of allowing too much pressure build up. If you can hold the jar upside down with water in it and water doesn’t leak out unless you pull pretty hard on the lid then it is hermeticaly sealed. As long as the seal is tight enough to hold a little bit of pressure inside, it is impossible for outside air to get in. What will happen is the co2 will build up to the point that the seal starts to leak and the excess pressure will push up the lid and seep past the seal. Once the excess pressure is released the leaking out of air stops and the jar seals and the inside remains pressurized. It’s the exact same as letting air out of a car tire. When you open the tire’s valve air rushes out but stops when you close it. At no point can air ever get into the tire because it is pressurized inside the whole time. The only way air can get into the tire is if you force air into the tire valve at a greater pressure than the inside of the tire. So the only way air could ever get passed the hermetic seal of the jar without you opening it is if the atmospheric pressure was greater than the c02 pressure inside of the jar, which will never happen unless you adjust the seal way to loose on a low pressure day. As long as it’s adjust to where it doesnt leak out water upside down until you pull hard on the lid, it will hold much higher pressure than the atmospheric pressure can ever overcome.

      • I just bought 4 Fido jars. From the factory, 3 of them sealed too tight and I adjusted them. One of them was perfect and needed no adjustment. Before I adjust any of my jars I fill them with water and do the upside down leak test and pull on the lid. The one that didn’t need adjusting started leaking out water when I pulled down on the lid so it was already perfect. Some of the jars straight from the factory already have a less tight seal.

  • Thank you for your great articles re: what to use for fermenting. I wanted to follow your link to buy the Pickl-It but just got taken to their website. Also I am in Australia so it seems Pickl-It do not ship to Australia. Do you have any ideas how I can get the jars – they look great. Thank you

  • David

    Another site did a test with the baking soda/h2o2 in a fido submerged after closing. Even with extremely rapid off gassing it just leaks out the lid. If people use a bit of common sense it is a pretty simple thing to take a towel and add slight pressure to the lid as they release the latch. No flying lid and a towel to soak up any liquids. How many million beer bottles are transported without exploding cases being held only by a crimped bottle cap? I buy fido jars for 1/6 the cost of picklit jars or less. If you really have a need to vent it get a high quality drill bit for the glass and use a wood form to guide the bit as it starts to dig in and 2 dollars later you can insert a valve.

  • David

    Here is also dr mercola who tests everything. Mason jars with loose lids 10 trillion probiotic count 5-7 days fermenting. No airlock, weights, or anything expensive.
    I found it interesting the short ferment time when I see most reccomending 3-4 weeks. Perhaps that is just a flavor or texture preference vs probiotic content.

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  • Rafael

    I have just pickles some cuces with Fido (Water salt mixture plus spices) jars, I wanted to keep them longer so boiled for 5 minutes and stored in basement. Every few days I go down there I keep find spilled broth from the jars, is this normal or will they go bad? I thought that if you boil them they stop the fermentation process, they look after two weeks like they are way ready and I wanted to keep them all winter, is this possible?

  • Susan

    I wanted to can Salsa from items grown in my garden. I usually use mason, However, I seen these amazing jars. So I just fill and clamp no boiling?

  • where do u get the dido jar with the cover with the air lock. thank you

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