Fermentation Friday: Why I Won’t Ferment Without A Separate Airlock Part I


I have been asked repeatedly to post why I will not endorse active fermentation in a Fido and what I have found about the issues of pressure, carbon dioxide build-up and such in ferments.  Do they produce ferments of the same quality at a cheaper price? If they hurt it, how much and what do I loose? Is a separate airlock really necessary or will just the seal that makes it airtight do?  These questions have been swirling for weeks.

I finally had the time this week to sit down and begin pulling my notes from the last few months together.  I will link to and discuss just a handful of studies in this first part. This is the first post in a series on carbon dioxide and pressure.  There’s more to come.  Many thanks to those of you who have waited patiently for this post, appreciating that real life and my family has to come first for even the busiest of bloggers. If you’d like to see more fermentation posts I have written, check out the Related Posts section below for plenty of links and great info. We also have a fermentation class where you can learn more about fermentation, how to use and care for the vessels and how to make a wide variety of ferments and you receive free access to our Real Food Cooking School as a bonus. We also have a facebook group if you’d like to chat with others.


Pressure and Fermentation

First, let’s discuss the pressures involved in fermentation. From the information I could find, a separate, three-piece airlock burps itself as low as .1 psi, depending on the type.  That’s pretty low. I couldn’t find any information about water moat fermentation vessels such as the Harsch Crock, however I must assume that they are similarly low, because they do not produce the characteristic pop/hiss that pressurized vessels give when opened (not to be confused with the hiss that can occur when gas is escaping through the airlock on a very active ferment) and you don’t see the mad rush of dissolved carbon dioxide returning to being a gas and rushing to escape. With this low of a pressure, carbon dioxide isn’t forced to dissolve into the brine and instead remains a gas, working its way up through the ferment and out of the airlock- that’s the little bubbles you see in the veggies and bubbling through the airlock. If the CO2 dissolves, you can’t see it.  All of the gas in a ferment being visible and having an easy route of escape while preventing any outside air from getting in is a good thing.

I found varying quotes for the psi of different ferments- for example, pickles average around 15 psi.  Psi is pound-force per square inch. A hermetic container with an off-gassing ferment in it that is very active (think water kefir) could easily build up pressures in excess of 15 psi, even if it does release small amounts of gas on occasion as some people have reported a Fido does.  I strongly suspect from personal experience and in talking with others that water kefir can go higher than that. A realistic pressure test would have to take into account both the psi, the varying pressures in the different stages of fermentation and the length of time involved in a complete ferment.

While some other options do, in fact, release some small amounts of gas, their ‘slow leak’ release maintains a high pressure in the fermentation vessel which keeps the carbon dioxide dissolved and other gasses trapped in the brine as well- gasses that can negatively effect flavor in some instances.  That is problematic.  It doesn’t matter if it’s a mason jar, Fido or something else, current research shows it to be problematic on multiple levels as both pressure and dissolved carbon dioxide have a negative effects on the good things you want to be in your ferments. Let me share just a portion of what I have found with you about how pressure and dissolved carbon dioxide negatively effects fermentation.


Carbon Dioxide and Enzymes

First, studies and patent applications are clear that the more dissolved carbon dioxide (CO2) that is pressured into a cell, the more it retards enzyme formation (Citations I, II,  III and many, many more). We can assume that since fresh vegetable cells and bacteria cells are both living, there will be a similarity in this function as the way carbon dioxide enters a cell through the cell wall appears to be the same regardless of the cell type, as far as I can tell from my research. No matter the type of cell, the cell walls of every type of cell are made up of lipids (fats) and function the same way. If that is incorrect, I am open to correction.

This perhaps explains why I was not able to discontinue taking digestive enzymes until I switched to an anaerobic method with an airlock- I used a Harsch Crock.  What is dissolved carbon dioxide and how do you know it’s in a ferment that doesn’t have an airlock?  We’ll discuss that below.  I am continuing to research the issues surrounding enzyme production and will share more as I form a more complete picture.


Pressure and Lactic Acid Bacteria

The pressure comes from not just carbon dioxide, but all of the gases produced by fermentation.  Multiple studies cite reductions in lactic acid bacteria numbers and reproduction the more the pressure is increased in an anaerobic fermentation chamber. (Citation I)

Pressurized carbon dioxide, called “high carbon dioxide” is currently being used as a way to inactivate bacteria and enzymes (Citation I).


Carbon Dioxide Levels and Lactic Acid Bacteria Growth

Multiple studies show the more CO2 a ferment is holding, the more you see a reduction in the numbers of the lactic acid bacteria. (Citation I)  Carbon Dioxide and oxygen together, which would be found in a brine, that is pressurized had the most devastating effects.

This makes sense to me in a very real way, as nothing I know of in nature thrives in its own waste.  You see, carbon dioxide is a waste product for the bacteria- they exhale it.  As Patty from Loving Our Guts pointed out in a recent discussion, things surrounded by their own waste do not reproduce and thrive as they would if the waste is removed. In a vessel with an airlock that doesn’t allow pressure to build, that waste product is released and removed, allowing the lactic acid bacteria to thrive.


The Final Nails in the Coffin

In another study, they took a lactic acid bacteria from a meat product and placed it into a brine then studied what dissolved carbon dioxide did to the bacteria.  The study stated “(Dissolved) carbon dioxide negatively influenced the growth rate of L. sake. A negative, linear relationship was observed between the growth rate and the amount of dissolved carbon dioxide.”

Let’s pause there- that is critical.  The more pressure a ferment is under, the more dissolved CO2 the brine contains.  The more dissolved CO2 the brine contains, the less the lactic acid bacteria grow and the fewer enzymes are produced.  We see another confirmation of what I discussed above.

How do you know those bubbles in a Fido are dissolved CO2?  Watch what happens when you open the lid- bubbles rise from all over the place, out of no where. Remember, CO2 that isn’t under pressure doesn’t dissolve, and it remains as bubbles. The pressure causes it to dissolve and you can’t see it with your eyes, until you release the pressure on the jar- the bubbles suddenly appear out of no where and rapidly escape the jar. The vegetable matter and the brine level literally heave and can overflow, the reaction of the carbon dioxide is so violent. Now that you’ve released the pressure, it is no longer forced to be dissolved in the brine and can return to its preferred state, a gas, and escape.  And escape it does, but your ferment has already been damaged by the pressurized carbon dioxide.

That’s all the proof I need to know I don’t need to ferment without a airlock that allows the ferment to stay at a normal pressure.  Pressurized ferments such as those done in a Fido without an airlock on top will, according to this study, inhibit the growth of lactic acid bacteria. How do you know if you have the right kind of airlock?  During a primary ferment, if you have a pop or sudden bubbling when you open the vessel, it is under too much pressure and it is negatively effecting the ferment.

In fact, dissolved CO2 is a big a problem in the pickle industry.  It causes pickles to bloat and expand, develop gas pockets in their middles and go yucky.  These pickles are called “bloaters.” A good bit of research has been dedicated to figuring out how to stop it from happening.  They recognize that allowing oxygen in can reduce the CO2 levels, but it will also cause off-flavors, spoilage and other problems, so oxygen is best avoided.  Their solution? They recommend bubbling N2 through the brine to remove the build up of CO2 (the N2 traps the CO2 and carries it out through an airlock) to keep the pickles from being damaged. That keeps the ferment both anaerobic and low in dissolved oxygen so the pickles don’t get ruined.


Want To Know More?

From the research I have listed in todays post coupled with the research and experiences I’ve discussed in my other posts on this topic, I’ll stick with my Pickl-Its and my Harsch Crock for optimal probiotics and enzymes until solid science proves there are other vessels that are anaerobic and allow gasses to escape without a problem.  If you want to read more about my research on fermentation or more about what happened to me personally when I switched, you can find a list of other articles I have written including studies.  Scroll down, they’re listed right above my picture in the section marked Related Posts.  You can also read a guest post I wrote about the specifics of my own gut healing through fermentation.

If you need help knowing what and how to ferment, our lactofermentation class is for you. This isn’t like other available fermentation classes as the material and the class is on-going, giving you access to new information continually. You can learn the whys and hows, watch me ferment in-season foods, have your questions answered and interact with other fermenters.  You also receive access to our other class, the Real Food Cooking School, for no additional charge.

We will continue this discussion and look at some other research on the topics of pressure and the effects of carbon dioxide in a future Fermentation Friday post or three.  Plenty more to come.


Fermentation Friday

This week, there are a number of fermentation posts from the bloggers in Nourished Living Network that might interest you.

Jennifer from Hybrid Rasta Mama shares how her recent Fido and Grolsch ferments left her cleaning up after a fido exploded in the kitchen and then a Grolsch sent 22-feet of spewed kefir from all over her kitchen, living room and couch, due to the crazy pressure and dissolved carbon dioxide as I discussed above.  She’s not the only person who has reported such explosions from both types of bottles- I’ve personally had a couple of Grolsch bottles explode on me and had a similar explosion from a Grolsch soak my ceiling when I opened it over the sink when doing second ferments on water kefir.  I’ve also had a mason jar with sourdough explode and make a huge mess.  She also recently shared a great post on mold and fermentation.

Lydia from Divine Health shares how she makes water kefir in her Pickl-It.

Patty from Loving Our Guts shares how anaerobic fermentation was the missing piece they needed to be successful on the GAPS diet.

Melanie from Pickle Me Too shares how she uses her bounty of chili peppers in this post, Pepper Mash and Chili Sauce. She also revamped her Orange Ginger Beet Kvass recipe. If you’ve tried making kvass and couldn’t stand it, this method might make you a fan.


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I'm KerryAnn Foster. I live in the mountains of Western North Carolina with my husband, Jeff, and our two kids, a teen and a tween. I blog here at Intentionally Domestic (formerly Cooking Traditional Foods). I blog about Paleo, beauty, health, family, homeschool and lifestyle for women in their 30s and beyond. I have over sixteen years of real food and natural lifestyle and health experience.

I am also an It Works! Global Triple Diamond Independent Distributor. I love that crazy wrap thing! I have been extremely happy with how the It Works Products have tightened up my loose skin and healed my stretch marks after losing 179 pounds and having a 10-pound baby.

Read about my journey to health through celiac disease, PCOS, food allergies, obesity, adrenal fatigue and heavy metals.
Categories : Lactofermentation


  1. Cory says:

    Great article KerryAnn! I look forward to the rest in the series 🙂

  2. Heather Tate says:

    I just really enjoy reading your blogs. When you are explaining the “how and why” of fermenting you really know how to explain it nicely. Thanks for making fermenting so clear.

  3. AmandaLP says:

    Thanks for the citations about the dissolved CO2 and pressure! Ive been wondering about those for a while with the airlock and Fido debate.

  4. Karla says:

    Kerryann: if I switch from a mason jar to a pikl it for my water kefir, do I need to throw out my old wk grains and get new ones? Thanks for your thoughts.

  5. Ellen Ussery says:


    What do you think of

    I have had great success with my Pickl-It jars, but thought that these might work as well and be less expensive , Especially if you have a closet full of canning jars


    • KerryAnn says:

      Ellen, plastic can warp under the pressure of fermentation, leading to air leaks and oxygen exposure once active off-gassing dies down, even if a ring is in place. A fellow blogger has used it and still had oxidation show up on the top inch of her ferments, so I have concerns about it. Honestly, anything plastic can warp and lead to oxygen exposure which is why you see the methods I personally use don’t have plastic bodies for the areas that take pressure.

      In addition, depending on the system, the salinity and acidity of the ferment can cause leeching from the plastic, however I don’t know what type of plastic this is made from so I can’t comment if that would be an additional concern with this particular system.

  6. Bethany Nash says:

    Oh, this is excellent! I’ve been wondering about this, and seriously considering fermenting in regular Fido jars. I’ll definitely hold out for the Pickl-It now. Totally convinced.

    Follow-up question: Can you move fermented foods from the Pickl-It to a regular Fido for storage after initial fermentation?

    • KerryAnn says:

      Bethany, once the active off-gassing is done and the airlock as completely dropped, then I swap the lid for a Fido lid and store it that way. It allows me to get more use out of the Pickl-It.

  7. Connie says:

    Whoah! Awesome info! Thank you soooo much for researching and sharing. It makes me think that a secondary ferment of kefir in a Grolsch/Fido to get the CO2 bubbles might not be such a smart idea. What say you???

    • KerryAnn says:

      Connie, I’m leaning towards saying that it shouldn’t be your primary ferment and if you have a certain goal of amount to consume daily, I wouldn’t count it towards that total, I would just consider it extra. That is what I am doing until I can determine otherwise.

  8. Monica says:

    Thank you for your incredible research. We are looking forward to building our collection of Pickl-It jars. I have a question: Is it ok to use Therapeutic oils for flavoring? It is food grade (Young Living), We love the flavor and wondered if it is taking away from the LABS. Thanks! ♥

    • KerryAnn says:

      Monica, I’m not sure about the essential oils. My concern is that I thought most essential oils are anti-bacterial, so it would potentially kill the LABs. If I can find anything more on it, I’ll d a blog post on it.


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