Can Fido jars defy science? Can they provide a fail-safe, spoilage-free ferment with no brine cover? Find out…

After completing Sauerkraut Survivor, I knew there was more I wanted to find out about fermenting jars. When I opened the Fido I was impressed with the amount of CO2 it holds (it was bubbling for minutes after I opened it, as you can see on this YouTube video I made). I had to do more experimenting.

In particular, I wanted to know: since the Fido has the advantage of holding in more CO2 than other airlock systems – could that be an advantage that would perhaps allow the sauerkraut to be spoilage-free with no weight at all? It can be difficult to find something that keeps those floaters down – and floaters seem to attract spoilage. It would be handy to not need a weight.

The Test

On July 8th, I filled a 1/2 liter Fido jar with salted cabbage (to make sauerkraut) – with no weight or even a cabbage leaf – and let it sit on my counter for four weeks.

At the same time I filled a 1 liter Fido jar the same – only I used the food-safe dehydrator screen as a weight so there was no cabbage floating. I love how clear the brine is with these screens!

The Results

On August 10th (yup, two days past 8/8) I opened them. All month long I was checking them for spoilage, seeing none, but I knew the big test would be checking the brine under my microscope. Sometimes the ferment can be visually spoil-free, and yet have traces of mold or yeast in the brine once you look at it under the ‘scope.

The photo above is the 1/2 liter Fido opened after 4 weeks. You can see the cabbage is clear out of the brine – we’re talking more than just floaters! If there was ever a set-up that would attract mold, this is it.

And yet, there was no spoilage!

This wasn’t even the freshest cabbage I could have used. You can see there isn’t much green in my ‘kraut. I used up the last two heads that were left over from Sauerkraut Survivor, and had to shed the outer wilted leaves to the point not much green made it.

And still, no spoilage!

Beyond there not being spoilage, the LABs were thriving like crazy. They love the protection the extra CO2 gives.

The difference between the Fido airlock and other airlock systems

The difference between the built-in airlock the Fido jar has and other airlock systems is this: your typical 3-piece airlock (like this one) airlock is installed on the top and filled with a small amount of water. The water acts as a barrier to prevent oxygen from getting to your ferment. At the same time, it allows the CO2 to escape through the water barrier. Any amount of CO2 pressure can work its way right out with very low resistance.

Similarly, the Fido’s vulcanized rubber gasket is an airlock. It keeps the oxygen out, while allowing CO2 to escape. The difference, though, is this: the CO2 needs to build up more pressure before the lid is lifted and the CO2 escapes between the rubber gasket and the glass rim. This allows for a certain amount of CO2, which is produced by the lactic acid bacteria, to stay inside the jar, acting as a blanket of protection.

Once you open the jar, you will hear the pleasant “pop” sound – you know you did it right :)

Fido jars defying science?

So can Fido jars really defy science? It seems so. From everything I have read, and experienced, you really do need a brine covering to prevent spoilage. Low brine levels caused several of the jars in my Sauerkraut Survivor series to spoil – and with good reason. As I explained in The Science Behind Sauerkraut Fermentation, moisture is one of the key elements in keeping spoilage at bay. Too low a water level will give oxygen-loving bacteria, yeasts, and mold the right environment to grow.

I encourage you to give Fido Fermenting a try! I was inspired to create a Facebook group for Fido Fermentation – feel free to join :)

Similar Posts:

Want to learn more about herbs?

proud contributor
Lea Harris founded Nourishing Treasures in 2006. A mom passionate about her family's health and well-being, Lea believes education is power. Encouraging others to take baby steps in the right direction of health for their families, Lea's goal is to raise awareness of what goes into our mouths and on our bodies, providing natural alternative information that promotes health and prevents disease by using traditional foods and nature's medicine.

Lea is a Certified Health Coach graduate from Beyond Organic University, and a Certified Aromatherapist graduate from Aromahead Institute.

"Like" Nourishing Treasures on Facebook, join the Nourishing Treasures Group on Facebook, follow @NourishTreasure on Twitter, and subscribe to our newsletter.

You can also find me on Learning About Essential Oils forum, and Fido Fermentation Facebook group.

Disclaimer: I use affiliate links wherever possible. So if you click on a link, and make a purchase, I might make a small commission, but it doesn't cost you any more.

Comment with Facebook



Can Fido jars defy science? Can they provide a fail-safe, spoilage-free ferment with no brine cover? Find out… — 21 Comments

  1. Lea, you are a champ! I’ve spent the last 2 weeks in a fog, reading the varied fermenting suggestions. I love your experimenting with the lot. And you’ve posted this follow-up at just the right moment for me. You’ve convinced me to keep it simple. Now I’m looking at new gaskets from some old jars I’ve sourced, either rubber or silicon. My brief research yielded more concerns about possible rubber contaminants than about silicon. I don’t know if they would be the same thickness. Have you encountered them?

    Also, your method might answer the following question for me. I’ve seen references to transferring fermented products into smaller jars, including to be able to use the pickl-it for a new batch. I can’t quite figure why this works, unless it’s because at this stage (which stage??) it’s ok to introduce O2. I would like your understanding re transferring, maybe as I keep exploring your posts I’ll find it. In any case, settling on Fido jars as my method let’s me purchase more of them, and relieve my brain of processing this issue. Thanks you so much, ahmo

    • I am comfortable with the vulcanized rubber gaskets that Fido uses. They are made so the chemicals are so imbedded into the rubber it takes a whole lot of work to get them released into your food.

      The thought is once your jar becomes half ferment and half air, the oxygen could overwhelm the LABs in the ferment and cause spoilage. I am not sure if this is just another myth I need to bust, or if it is in fact true. I personally feel (real scientific, eh?) that you’d be introducing so much more oxygen by pulling it all out of the jar and dumping it into another. I have not tested this yet….however I do have a 1 liter jar of sauerkraut that I have been eating out of – without refrigerating – for 16 days now. It’s less than half full and still no spoilage. Could it be the Fido? Could it be that it’s at such a point, pH-wise, that oxygen doesn’t matter? I don’t know. I will be testing it for spoilage (under the ‘scope) soon and will publish my results. So far I have found you do NOT need to refrigerate as long as you have properly fermented first. I let this one jar ferment on my counter in a Fido for 1 month + 2 days before opening. The LABs were high, the pH was low – perfect.

  2. And another thing….about how to get enough probiotic juice from the veggies. I’d been happily making and using kvass, which, according to Sally Fallon, takes a week to ferment. Now that I understand I’ve been having a histamine response to the beets, that’s out for me. Is there any other veg that ferments quickly, like a ‘short pickle’? Or do I just need to keep putting things up with enough time and quantity to use after 8 weeks? Thanks gain for your comprehensive fermentation info.

    • Unfortunately, these things take time. I would stagger the ferments to be sure you always have some available. If you ferment just on your counter (do not refrigerate!! it slows the ferment down to the point of possible death) it only takes 4 weeks to get a super high probiotic count. I have a experiment going now to test the difference between a 4-week, 8-week, and 12-week counter ferment vs the popular “7-10 days on the counter, 12 weeks in the fridge” method. Wouldn’t it be wonderful to get as many or more LABs in 4 weeks on the counter than 12 weeks in the fridge?

      Fruit ferments quicker than cabbage and other veggies. I have not experimented with them, though.

  3. Your timing is perfect! Just making sure I understand you correctly…it’s ok if sauerkraut is not covered with brine if it is in a Fido jar? I have a batch going right now that I started a couple weeks ago. A couple days into the ferment, the brine began seeping/fizzing/spraying out of the jar & now it looks like there’s none left, at least not at the top. If I tip the jar a little, I can see there’s some further down. I had been wondering if the whole thing would be ruined because of the brine loss or if it should still be ok. Thanks much. =)

    • I admit I haven’t made beet kvass myself – I keep forgetting to buy beets :)

      When I do, I will use this recipe:

      Place 3 beets (scrubbed well, chopped in 1/2″ cubes) in 2L Fido, fill to shoulder with salt water (1 TBSP dissolved in warm water on the stove, then cooled before filling in Fido).

      Most recipes call for whey – you don’t need it. Most authorities tell you 2 days on your counter, then in the fridge. I would do at least 1 week, if not 2. I will play around with the times and let you know :)

  4. Hi Lea,

    Your experiments have proved invaluable to me as I start fermenting veggies, and I’m really grateful for the Fido Fermentation group on FB!

    I am very much looking forward to the results of the experiment you mention above re: refrigeration vs. leaving ferments out on the counter. I have just put my kimchi in the fridge after 7 days, and it tastes delicious, but I’d hate to learn I’ve killed all the good bacteria when I could have just left it on the counter! Is this what you recommend – just to leave ferments on the counter? For how long? When do you refrigerate, if you refrigerate at all?


    • In a week or so I will have the results for the 8 week counter ferment to compare with the 4 week counter ferment. I am sure it will show more LABs. I can’t wait to see, in a month, what the 12 week counter shows in comparison to the 12 week fridge ferment! :)

      I don’t think you necessarily “killed” the good bacteria, but they don’t do as well in the fridge. The LAB count likely dropped off quite a bit. This is a hypothesis of mine after learning the temps they prefer, but I won’t know for sure until next month when I compare the 12 week counter ferment to the one in the fridge. I suspect the 4 week counter ferment (or at least the 8) will have more LABs. Time will tell!

      What I can tell you now (I haven’t had time to post about this yet) is that I have left sauerkraut on my counter 4 weeks, then opened it and ate out of it going on 4 weeks now and it has not spoiled. So yes, I do recommend just leave them on the counter. I prefer the taste – it’s sweet/tangy/salty and has some crunch. Delicious :) I will have it eaten by the end of the week, so I would say if you eat it within 4 week’s you’re all set. This is of course speaking of Fido ferments only – I am not sure that I would trust airlock systems since the extra CO2 seems to be helping.

  5. Thanks so much for sharing your experiments Lee. 3questions: When fermenting in the fido jar, do you fill the jar up past the shoulder ? (it looks like you do in the photos here, at least with brine if not solids). Secondly, I have been putting my cabbage and other veg through a blender so they are liquified before fermenting, rather than just chopping them. This would make them ferment faster, wouldn’t it? And thirdly, summer is coming up here (Australia) where it gets very hot (up to 45C at the hottest) ……would you imagine from your experience that beyond a certain temperature, it WOULD be best to refrigerate during fermentation to get the best LABs ? I know that’s a lot of questions – any response very much appreciated – thanks so much :-)

    • I try not to fill too much past the shoulder (especially the cabbage). The photo was taken after it sat, so the brine level did rise during that time.

      I am not sure if the ferment time would increase – it’s possible that it might. Wonderful question, though! I don’t believe I’ve heard of anyone blending it first. I would love it if you could post that question on Fido Fermentation.

      LABs are comfortable up to 112F degrees. Over that, I would try and put it in a cooler with ice, or find a cool spot in your house. LABs don’t like temps under 50F, so I don’t recommend the fridge.

      Let me know what you decide to do and how it goes! :)

      • I guess I don’t understand why it’s important to leave that gap at the top. If you want to keep oxygen out why not fill with brine all the way to the top and just expect a little more mess from a few more burps?

  6. Pingback: r.r. alder

  7. Pingback: Four Things You Probably Don’t Know About Fermenting Vegetables

  8. Pingback: Easy to Make Sauerkraut — Granny's Vital Vittles

  9. Pingback: Fido Fermentation…My New Food Preserving Obsession! | Pamela Farms

  10. have you tried this in other brand jars that were fido style that weren’t the Bormioli Rocco brand? Just wondering if the ones made in china/indonesia are just as airtight?

  11. I can’t seem to find an answer to a question I have about Fido fermentation. Katz is always talking about tasting kraut throughout the process. But if using a Fido without a weight (as I am now doing for the first time) it’s the CO2 that keeps out the oxygen, so does that mean it shouldn’t be opened for the occasional tasting? After opening does more gas come and force out the newly introduced oxygen? Should I switch to a weight after sampling? I did just try some after day four . . . pretty good stuff and I don’t want to ruin it. P.S. thanks for all the help I’ve found on this site. Definitely made me more confident for this first run.

Leave a Reply