A Warning About Fermenting in Fido Jars

Fermenting in Fido Jars

We’ve talked about  a few different vessels you can use for fermentation and one of the favorite jars of many is a plain and simple Fido jar.  It’s a wire bale jar imported from Italy.  I love these jars to the point where I may have a slight obsession with them

Is it safe?  Honestly, if you want to do it, I’m not stopping you.  Here is the deal though, fermentation is not what these jars are intended for.  It’s been said that the jar’s wire bales are made flexible enough to allow gasses to escape as part of the canning process, implying the same should be true for fermentation but that’s just not true.  They are intended for canning and storage purposes and that’s it.  Fermentation creates much more gasses (read pressure) than canning.

I emailed Bormioli about it a while ago but received no response.  I do believe they aren’t saying anything period on the topic.  But I did get an interesting comment 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 comment:

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.

–Robert Lieberman,

So of course this peaks my interest and I email Robert for more information.

Here’s the deal:  Most jars should be able to hold up to the pressure of fermentation.  Most but not all.  Fido jars are annealed which means once they leave the mold, they are put right into an annealing oven, heated back up to 2,000 and then the temp is slowly lowered.  This process makes the glass stronger than glass that hasn’t been annealed.  Other glasses (from Asia, Eastern Europe and Mexico) are cooled in less than a minute so they use a thicker glass to make up for it.

Even thought Fidos are annealed, there is still a chance of thermoshock fractures.  A very small chance but it’s there.  The jars are inspected by human eye with a fluoroscope at 20 jars every 2 seconds and jars with visible thermoshock cracks are discarded.  But some get through.

This is not meant to scare you, this is just meant as a warning.  If you are fermenting in Fidos (I admit, I do it when I run out of lids with airlocks), be careful.  Like I said in my other post, vent the jars daily.  If you own as many Fidos as I do, you’ll know some jars balings are tighter than others.  You might want to vent the tight ones daily or don’t use them during the active fermentation stage.  It’s simple to do, just lift the lever until you hear the gasses escaping and then seal it up.  The gasses will build up again so if any oxygen did somehow get in while you are venting, it’ll be pushed to the top.  I’ve not had any visible problems with mold or oxidation using this method.

I do still prefer to use an airlock so I don’t forget to vent.  Plus, I’m still unsure about the effect built up CO2 has on a ferment.  Keeping a Fido closed will build up enough CO2 to push it back into the ferment making your pickles fizzy, not just the liquid.  Kinda cool but I’m not sure how it affects the health of the ferment.

And as far as Mr. Lieberman being in “collusion” with their customers?  That’s just silly.  GlasPak sells Fidos with or without the hole.  Heck, they probably make more money from selling Fidos intact than to companies that drill holes in the lids.

ETA:  While this information pertains specifically to Fido jars, the same holds true even more so for other wire bale type jars.  Fido jars are high quality where most other wire bale jars are not as awesome.  I will not ferment in a jar that is not a Fido jar even with venting.

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63 comments to A Warning About Fermenting in Fido Jars

  • Tiffany

    I understand all of this but can you explain when/if you remove the airlocks. I was thinking that once the food is moved to cold storage, the airlock could be removed. For instance, I left my pickles sit out in a fido jar with airlock for 10 days. On the 10th day I removed the airlock, plugged the hole and moved it to cold storage. Should I be burping it regularly or putting the airlock back in?

    • Ideally you would want to leave the airlock on in the fridge for a week or so while the activity dies down but who has room in their fridge for that? I do put regular lids on right away and just burp them occasionally in the fridge.
      Unless you have a low profile airlock like on the Boss Pickler. Those fit wonderfully in the fridge.

  • 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.

  • Alex

    I ferment in Fido jars, and what I do is burp the jars during the first few days, when gas production is highest. By burping, I mean lifting the bale mechanism just enough for gas to hiss out but not allow air back in. To be honest, my primary reason for doing this is to expel oxygen from the jar as quickly as possible, but it also has the effect of preventing excessive pressure levels.

  • Heather

    Interesting and timely article as I am just starting to ferment!

    Does anyone have any experience with Weck jars for fermenting?


    • I love Weck jars and wish they were good for fermenting but the clips that hold the lid on are only meant to keep them in place for canning. They don’t hold the lid down tight enough to keep the air out.

      • Seth

        Hi Melanie, how often would you open a fido jar to release air versus refill the water in a harsch crock or airlock which wastes water and allows mold to get in there in my experience. I want to be as maintenance free and mold free as I can. Thanks!

        • Never. Opening the jars defeats the purpose of using a fido to ferment. Opening will allow air into the container which is exactly what you don’t want. There are no recorded instances of FIDO jars exploding, most likely because they don’t explode. The fact that they were not designed as a fermentation jar is irrelevant to the fact that they work better than crocks and airlocks for fermentation. Fill the jars, seal them, stick them in a dark place and let them be until you want to eat the contents.

          • Sara

            I personally had a Bormiolo Rocco 2L Fido explode with a plain kraut on board. Temp was 71-73F and it was around Day 10 to my best recall. I had been reassured the jar self vented. I am diligent about not overfilling and also make sure the gasket and glass are clean and dry prior to sealing. I am not alone, several members on the Facebook group Wild Fermentation have had it happen.

  • […] #10 A Warning About Fermenting in Fidos […]

  • Bonnie

    I have 4 Fidos full of kraut, and they’re definitely heaving, with liquid coming out around the seal, lots of gas activity visible in amongst the cabbage shreds and some white foam on the outside of the jars at the seals. Should I open the jars and clean the seals? Add more brine? This is the first time I’ve ever made kraut.

    • For future reference, you don’t need to do anything. Leave the jars alone. Cleaning the foam off the outside may help prevent the salt from corroding the bales. Next time, only fill the jars up to the shoulder and then it shouldn’t overflow.

      • Seth

        Actually my jar was filled to the shoulder and it did overflow twice. You need to make sure your temperature stays at or below 70 degrees in this stage or else it will be overactive!

  • SanDiegoCathy

    Bonnie, I don’t have the answer, but your making my mouth water for sauerkraut!

  • Doesn’t all this burping introduce more oxygen into the ferment -something that is undesirable for an anaerobic ferment in the first place?

    • Alex

      I spelled it out very specifically in my reply above: burping is lifting the bale just enough for gas to hiss out. That doesn’t open the jar enough for air to flow in.

  • Beverly

    Does anyone know where you can purchase replacement lids for the Fido jars? My husband has drilled holes in most of my lids for the Boss Pickler valve, and I’d like to have a few replacement lids to use when I don’t need the valve.

    Last fall I used six 5-liter jars to make sauerkraut to eat daily throughout the winter. I love the Boss Pickler and have not had a single mishap with any of my fermenting projects, and I have never had to open the lid during the fermentation process. Furthermore, I have not had any yucky stuff to form on top.

    By the way, I have found the cheapest Fido jars on the web at Shipping was free if you spent $60.00. They also carry silicone or rubber replacement gaskets for a reasonable price.

  • Bonnie

    I haven’t ever seen just the glass lids for Fidos, but I found a great price on jars and lids at Their Fido rings are $2.49 a six pack. Their jar price is good, although the only size they have is the 5L unless you buy a package with salt. The 5Ls are $7.95. I don’t know if their shipping is good or bad. I had to do a search of “Fido” on that website to come up with the jars, in case anyone wants to look. That will bring up the gaskets, too, and a few other Fido things.

  • Beverly

    I could not find any Fido jars listed for sale on the, but Crate and Barrel has several sizes of Fido jars on sale with a flat shipping fee of $6.95.

    I’d like to see other comments comparing the Fido jar used with airlocks and/or the Primal Kitchen’s Boss Valve.

  • Cristian Mihai Sadean

    Hi all,

    Coool useful blog! …btw seems that the internet and the gobalization is making the world very very small. So I got the Fidos as well from an outlet and made the below:


    I’ve made the salts and herbs/spices liquid, boiled it and pore it over the vegetables including grapes… and normally they strted to ferment the next day, what I did notice is that at a certain pressure the gas escapes, plus the top of the jar is the strongest part, so I strongly beleive nobody should worry to much, even though I keept them in a fridge a day and added some extra salt and vinegar. Also the extra CO2 on top is a very good insulator for whatever you are fermenting.

  • John

    I have come up with the perfect way to ferment on the cheap.No expensive fido jars needed.
    Buy Mason Jars, plastic lids, food safe grommets (50 for 5 bucks on and rubber seals for fido jars of the same diameter as the mason jars and fermenting air locks from your local brew store.
    Drill a hole into the plastic lid to permit the grommet to be inserted tight. trim the fido jar rubber rings to fit into the plastic lid. Insert the air lock into the grommet. Now you have a seal that is tight and will do a perfect ferment. The plastic is food grade and the pressure will never be high enough to rupture it. After the regular ferment is over take of the lid, install regular tops with rings and store the container in cold storage or fridge letting the left over ferment and pressure, vent about once a week until the secondary ferment is over and the pressure is so weak that it doesn’t need venting anymore. If you still want to store it in fido jars for convenience, you can transfer the contents into it after the first (most active) ferment.Just make sure your jar is sterilized. The short exposure to regular air doesn’t hurt the contents.

  • BB

    Fido jar will not explode during fermentation because the pressurized CO2 gas generated by the LAB will be released through the plastic seal ring. The great thing about fido jar is that the ring does provide a air seal but also able to release the pressure inside the jar at the same time!

    I just made a new batch yesterday and now gas and some brine are leaking out due to increased brine level.
    i just clean the leaked brine and will not open it for another 3 weeks for tasting.

  • Every single person posting here that is fermenting in a non-air-lock-vented vessel is putting themselves and their families and the world in danger not only from exploding glass but also horrific pathogens that can only be cultivated in aerobic conditions. You have been lied to by the cult of ‘lacto’ fermentation by people who have no knowledge in the science of fermentation. You have all become the New Typhoid Marys to spread pathogens that you created in your bottles to the rest of the world.

    • Alex

      Not true. Fido jar’s have been found to vent themselves, as the bale and gasket function as a check valve, which is vastly more effective at keeping oxygen out of the jar than a water-filled airlock. In a Fido jar, outside pressure pushes down on the lid, sealing the jar more tightly; pressure inside the jar pushes up on the lid, loosening the lid just enough for air and CO2 to escape. By contrast, the little column of water inside an airlock lets gas flow from the high pressure side to the low pressure side, regardless of whether the high pressure is inside or outside the jar. Water based airlocks will allow air to flow into the jar if the outside pressure is greater.

      Pathogens? That’s what the salt and low pH is for. BTW, Clostridium botulinum is an obligate anaerobe, and salmonella is a facultative anaerobe. What are these aerobic pathogens you think will grow in the absence of a water airlock? I’m not saying those little airlocks don’t work; they do. But, there is simply no absolute need for them. Pickles and sauerkraut have traditionally been made in open barrels. Anaerobic fermentation vessels are a convenience in that they prevent aerobic organisms from forming on the surface of the brine.

    • Sara McCoy

      There has yet to be one confirmed case of food-borne illness from properly lactofermented food worldwide. People are scared that they will get botulism, but the process of proper lactofermentation inhibits such bacteria (and many others). It is when people don’t do things the right way like using alkaline water or topping with oil as the ferment starts that the stage is set for disaster. Preservation of food via lactofermentation, ie wild fermentation, has existed for century upon century. Fearmongering is typically done by those who have no practical experience and no grasp of the process (the science behind it).

    • Tamara

      Yes. Here is a good article about why Fido jars are structurally unsafe to ferment in without an airlock:

  • klab

    I’ve been successful fermenting vegetables for years without the use of expensive specialty jars or air locks. The key is to keep everything fully submerged underneath the brine by at least an inch. I use regular mason jars although I skip the metal bands and lids and use the plastic replacement screw on lids sold at Walmart. A sleeve of about 8costs less then $2. I did purchase glass weights to help hold things down under the brine for coarsely chopped vegetables or sauerkraut but when making pickles I simply cram everything in super tight so they won’t float above the brine. I unscrew the lids once a day for a few seconds. I’ve never had any ferment go bad and I’ve never had issues with scum or mold. It’s not necessary to spend money on expensive fermentation gear as long as everything is clean and you don’t let anything float to the surface or beyond.

  • Regena

    I also ferment in fido jars. The rubber gasket ring lets gas out but not air in. Even used a large one to make wine. Haven’t had an issue with them breaking so far.

  • Well this has been an interesting read… so let me be very clear again. I am direct importer of FIDO jars from Italy – in the 60’s-late 80’s ‘s we were the SOLE distributor for Fidenza and when Bormioli bought them – they honored our contract, which expired in 1988 (my previous company that was sold in 1995) . Since then my relationship with Bormioli has been great – and we in fact are the VERO represetative for them on Ebay – appointed by the factory because of so many fake jars using the trademarks. Now it has finally calmed down and ebay to be clear is NOT a great site anymore with the China made junk flooding the market.

    FIDO jars are NOT made to self vent – I repeat – they are NOT made to offgas anything – and canning with a fido – when you seal down the lid from the hot bath is meant to create – not release pressure (those who can will understand the concept of an air tight seal) .. the seals are not meant to let gas escape – because if gas can escape and the jars end up with less internal pressure – than air can come in. Think what happens when you are at higher elevations and then go down to sea level with a product or for a visual … ever see a plastic bottle on an airplane become compressed when you fly?

    As to exploding jars – think in terms of the fact that millions (and I mean many many many millions) of jars are sold worldwide. The USA is among the smallest markets for this jar – go to any European market – you find this is the jar of choice for most quality products.. in the USA .. not as much – as in fact the cosmetic market was the major user for salt scrubs – the jars don’t leak (get it? they seal air tight) .. for years the largest user was Origins (Este Lauder) – I should know – I sold them over 2,000,000 pieces a year in our hayday .,… now they went to plastic 10 years ago – and ask the counter people how that worked out for them .. (*they leak – but are much cheaper in plastic)

    On a last observation – and back to exploding jars – just because you don’t know of anyone – or claim “no recorded case” .. that is not true – and will never be true … that is why we all carry product liability insurance. It happens – and we never lost a case – as when a product is used in a manner not intended – the manufacturer bears no responsibility – and fementing without a vent is a MANNER NOT INTENDED (note – the label and ads say canning and storage ONLY) ….

    Now I have no ax to grind with anyone – I love the fermenters – they are a huge source of volume for a great product… much like Colorado, Washington, Oregon and CA are now a huge source of volume for quality air tight jar (you figure that one out 🙂 ) .. but to think the because I supply Pickl-it a huge volume – I am in “collusion” with them … that IS laughable – I have a great relationship with a repeat and valued customer – but I also have at one time or another sold EVER other company named in these blogs… I have been in this business for a long time -my wife and I own it – and we do not give exclusived to any company .. in fact we sell these jars to the Smithsonian Museums – yep .. .storage of many items that has to be in an airtight vessel that can handle chemicals is done in FIDO jars (among others we sell them) … so please – let’s just look at facts on product – if it works for you – great .. but remember – it is MY job to remind people that the usage factor is important – in compliance with factory intent.

    On gaskets – there are many China made copies out there – they are NOT FDA approved – so watch what you buys- retailers as rule don’t care what they sell – they are profit/price driven.

    We do NOT sell the lids drilled .. that was an error in posting.

    Now happy fermenting .. and thanks to all who purchase FIDO jars – many of those came originally through my company.

    Robert C. Lieberman, Glass Packaging Solutions LLC and an Amazon large volume vendor by the way!

    • knitbunnie

      Have you or Bormioli actually tried fermenting in a genuine Fido jar with a genuine seal, straight from the company? I have bought many Fido jars by the case, and yes, they are genuine, sealed cases from a reputable seller, not from eBay. When one ferments in Fidos, they off-gas, and liquid can and does go out through the seal, as well.

      Have you ever canned, as in using a water bath canner or a pressure cooker? The jars most definitely off-gas during the canning process, too. How do you think the air gets out of the jar to form a vacuum seal? It goes OUT through the seal. If the lid was completely sealed to prevent off-gassing, the jar would explode in the canning process as the pressure built up from expanding gas.

    • Alex


      I think they’re just covering their butts in terms of liability. Sure, Fido jars are not intended for fermentation. But, the fact remains that they are awesome for that purpose.

      In any event, as I pointed out above, burping the jars for the first few days eliminates the risk of explosion and more quickly vents off the oxygen.

    • Dean

      Sorry Robert, but I must correct you on your comment regarding canning with Fido jars. They are indeed meant to release gas because in the canning process that’s exactly what happens. The jars are submerged in a boiling water bath. This creates pressure inside the jar when steam is produced by the heating. The steam pushes the air (oxygen) out past the gasket in the same way it happens with a Mason jar. That’s why you don’t tighten the lid. If this did not happen, or when it doesn’t happen properly, you create a sealed environment for aerobic bacterial to bloom. Once the air has been purged and the jars start to cool it creates a partial vacuum in the jar. The pressure differential…vacuum on the inside, atmospheric pressure on the outside, pushes the lid tight against the gasket creating a seal. As a result, there is anywhere from 5-15 psi of pressure on the outside of the jar, much higher than any pressure that might be formed as a result of the fermentation process going on inside the jar. Unless, of course, someone has modified the bale so it holds too tightly on the lid.

      I’m sure the intent of the Fido jars was not for fermentation, but that doesn’t mean they are unsuitable for the purpose. There is always a risk, but the conscientious person that takes the time to learn about the process…the physics as well as the science, will not have a problem. I’m not telling anyone to use Fido jars…that’s your choice, but personally I feel totally safe using them and will continue to do so.

    • Nate

      Robert, whether or not the Fido jars were developed to off gas is irrelevant. What’s relevant is whether or not they can in fact handle it safely, which they can, as long as they’re adjusted correctly as demonstrated in the video above. All most all of my Fido jars came adjusted for safe off gassing from the factor. There were one or two that I felt were a little to tight of a seal that I adjusted.

      There is enough adjustment range to where one can make the lid have virtually no clamp pressure, so it’s possible to adjust the bail wire to where the jar off gasses with the same amount of resistance as what an air lock has and yield the same results, as far as co2 retention.

      The pickl-it jars are way expensive, and an overly complicated unnecessary system, with increased maintenance. There is a much better, cheaper solution, and that’s plain old Fido jars with properly adjusted bail wire. Zero chance of explosion and you can set the off gas pressure wherever you want.

  • Knitbunnie … You are supposed to leave the latch up with the catch over it during canning .. just to point out the proper instructions. You then seal it after the process and builds the proper sealing pressure. The instructions are on the back of the little paper used to ship and seperate the glass lid from the jar, I believe (or they used to be)

    I am not here to argue with you … do whatever you want, once warned – believe whatever you want … but yes as Alex rightly points out – the liability issue is paramount as the jar may be awesome for your style of fermentation – and those who religiously vent them – but they are NOT meant for fermentation without a vent.. I am sorry if the facts from someone in this business bother so many of you .. but one thing you can’t deny – these are the fact and all readers of these blogs should be privy to the “other side ” that meaning the sellers and the manufacturers.

  • Dean

    I’ve used Fido Jars for canning and fermentation for a while. Have never had one explode. I suspect that an exploded jar was cracked before it was used for fermentation. Check the jars carefully if you want to use them for fermentation. If you do not feel safe, do not use them…period!! Find another method, for crying out loud! There is no debate…safety is paramount. Just FYI, when I do use Fido jars for fermenting, I can hear the gas escaping from the jar as it sits on the counter. Another option is that there are thinner gaskets available on Amazon that allow the gas to escape at a lower pressure. Happy Fermenting!!!

  • Mark Myers

    hello everyone. I got here looking for fido jars for making “kraut”. I have a degree in engineering and love solving problems. I’m good at it because I try to understand “what is going on”. I have been making kraut and fermented veggies in canning jars for a year or so. Here is what I have observed and understand.
    1. As the ferment begins, the liquid is released as the bacteria give off CO2. Way more than your jar can handle. I have been pouring it off and saving it and slowly putting it back. If it isn’t put back, your fermented stuff will be dry. This really doesn’t hurt anything, I just don’t like wasting all that liquid.

    2. I “bleed” the jars several times a day. The canning lid, which normally “pops” in when the jar is sealed, can be sprung out because of excess pressure. I let this happen once just to see. A problem with canning bands is…the brine is acidic, and causes corrosion of the band. looks ugly at the end of the ferment, leaves corrosion on the glass. won’t hurt the taste of the ferment if it doesn’t get “in”.

    My kraut seems to ferment longer than my veggies, even though the mix is about 80% cabbage. By “veggies” I mean cabbage, celery, bell peppers (red, yellow, orange… NO GREEN ONES), garlic, grated carrots and or yams or sweet potatoes (or all three 🙂 Absolutely no onions! it takes a week to ferment and just stops. I put it in the refrigerator and the stuff keeps easily for several months.

    3. as far as blowing up a jar, it would take several day to do that. If you bleed the jar at night before bed, it will not generate enough pressure to break anything. What I like about the FIDO is not having to take the lid all the way off and allowing OXYGEN into that space, which is the prime reason for spoilage.

    I would NOT be afraid of using a genuine “FIDO” jar made as it should be. I would be very leery of cheap knockoffs coming from “other countries”.
    Thank you for the informative article and for listening to my comments.
    Mark Myers

  • Dave

    The proper canning use of a FIDO is the same as all boiling water bath (BWB) canning. You fill the fido with your food product, close the wire bail half way, submerge the jar shoulder deep in boiling water, process for 5 to 15 minutes, then close the wire bail and remove the jar from the BWB. As it cools, it will create a vacuum (negative pressure), creating an airtight seal suitable for long-term storage.

    The fido lid system is designed to become an effective seal for a “negative pressure” or “vacuum” environment inside the jar.

    In terms of pure physics, the ambient external pressure exceeds the jar’s internal pressure, causing a constant external force pushing the lid against the gasket.

    Fermenters are using the fido backwards. They are creating a positive pressure environment inside the jar. The lid-gasket-bail system on the fido jar is not designed or intended to hold the lid tight;y shut against a positive pressure internal environment.

    The smallest fido jars will be the best at holding internal positive pressure, because the rigidity of the bail relative to the gasket surface area is more conducive to a stronger seal.

    The 2L size and larger jars will easily vent positive pressure if you just grab the closed lid and lift one edge of it. You’ll hear it hiss.

    IMO, my fido jars vent themselves whenever internal pressure exceeds 4 or 5 psi.

    But anything is possible. The fellow who posted the idea of modifying the bails to ensure that all of them are relaitively weak has the right idea.

    The goal is to avoid that one-in-a-million chance of exploding a forgotten fido.

  • Mike P

    Is it possible to get/purchase an extra lid or two for the Fido jars. If so who do I contact?

  • I’m new to fermenting vegetables and all I have is the Fido jars I love them and have not had a problem with them but I do open them daily to let the air out so thank you for your post and the warning because I wasn’t doing it every day. I use Himalayan pink sea salt I know you’re not supposed to use salt with no iodine in it but what is the difference between using the pickling salt and Himalayan pink sea salt? Does anyone know? I also wanted to use links from my blog to your blog for an upcoming post I’m going to do for design for healthy living…

  • jim

    i place my fido ferment jars in a covered stockpot until they’re finished and ready for use..i never burp the lid or worry about exploding jars, if it were to explode everything will be contained in the pot, no big deal..dump it out and pretend it never happened! by the way i’ve made many a batch and never lost one..

  • Judy

    Can you use old quart canning jars that have the glass lid & wire but just not use the rubber seal? For fermenting?

  • Lance

    This was an interesting blog. Some of the things I read I thought, really? I have about 120 Fido jars from a pint to 4L that I have used for the last five years fermenting all kinds of things. I close the lids after I fill the jars and leave them on the counter with the warmer temperatures for a day or two. Then I put them in the basement where it never goes above 60 or 65 degrees. I don’t open them until ready to use, and I have some jars that haven’t been opened for four years. In every case, the ferment is as fresh as can be and I’ve never had any mold. It’s impossible for air to get in since the CO2 pressure on the inside is higher, and the jars may self vent if the pressure gets excessive, but never so much that much liquid is lost. I’ve never given a thought about the jars exploding. I can’t see anyone having a problem when they are stored in a dark and fairly cool place. Right now, I’m enjoying a fermented basil pickle that made August 10, 2016 and it’s still as crisp and crunchy as can be. Mostly I use garlic and dill, but I like to experiment, and this basil pickle has a very nice flavor. Besides the basil, I also used onion, black pepper and added one garlic clove for good measure. I’ll be making more of these this year. Another very nice flavor is fennel. So don’t worry about using Fido jars. They are the best way that I’ve found. There is no way I would use 100 plus jars with air locks. What, and keep checking the locks for adequate water all the time and risk spoilage if any run out? Before the Fido’s, I used mason jars with the screw top lids. Now those had to be vented and it was always a pain figuring out when to stop venting in order to keep enough pressure inside to prevent air getting in, so it could get scary. One time a lid was buckled up so high that the lid was bent. I had to stab it with an ice pick to release the pressure since I would not have been able to unscrew the lid. Needless to say, the Fido jars are like heaven to me.

  • Frank R

    Fido jars have been used for over a century for fermentation. They do not explode, even when adding vinegar and baking soda.

  • Capt. Obvious

    Just put a weight on the top. No need to close the bail. Take the surface area of the lid and calculate the weight needed for 1-2 Pounds Per SQUARE inch.

  • Val Colvin

    I’m having trouble finding information on my question…and searches kept bring this post up, so I thought I’d ask.

    I’m making Kumbacha …and have never done a second ferment because I don’t have the wire topped tapered jars. I do however have hundreds of the old wire topped mason jars with rubbers. Can I safely ferment vegetables and kimbacha in them? Thank you for any help!


  • Stephanie

    OK, everybody is a scientist but missing the simplicity of the obvious way to release the C02 without introducing oxygen and eliminating any chance of explosion. Pull on the rubber tab that sits on the outside of the glass lid. We are talking about a rubber seal, correct? Pull on the tab a few times everyday. You will hear a “hisssss”. Am I just waaayyy too practical for y’all or is there somethin I don’t get.

  • Andrew

    Some Fidos do explode when fermenting, but you will find they are the square shaped jars because the internal pressure is not evenly spread throughout the jar (more pressure is formed in the corners of a square jar). If you use the larger round jars (4L & 5L), you will never have a problem as the internal pressure is evenly spread and they vent themselves before explosion. Also, instead of pulling the rubber tab you can make a small razor slit across the width of the rubber seal, long enough to span the thickness of the glass rim of the jar so that it automatically spreads itself with too much pressure and vents well before a fully sealed lid would do, just as extra precaution.

  • Mel

    So I keep the metal wire lock open and wind a small rubber ring around the wire locking mechanism to force the lid down, just tight enough to conpress the Fido’s seal. Any pressure would lift the lid.

  • jason findley

    Who would ferment without an airlock??? I think anyone planning to do any fermenting is going to use the vented lids with airlocks. Otherwise of course, any sealed container is at risk of explosion! Seems a bit of a non issue here.

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