Do I need an airlock to make sauerkraut, kimchi, and other fermented foods?

cucumber dill and garlic pickles
ready for the inner lid and weight

There is a lot of debate out there as to whether or not you need to airlock your vegi-ferments.  People are very passionate and sometimes a bit carried away.  There is supporting evidence for both sides, but as you may have noticed I prefer the open vat method.  In this post I would like to give you a simple overview of the debate and tell you a bit about why I decided that the airlock is optional.



To start with, some definitions:

This topic is mostly about fermented veg, like sauerkraut, kimchi, pickled cucumbers, hot sauce, whatever.  These are processes that use bacteria to transform and preserve foods.  We aren't talking about alcohol ferments like mead and cranberry mead which are primarily yeasted based transformations.

Wild cultures or fermentation is a process that takes advantage of yeast, bacteria, and other invisible beasties that live wild in the air and on the veg.  Cultured cultures and fermentations, sometimes called seed  or starter cultures, utilize a specific starter culture or bacterial addition that you can buy or grow yourself.  So for example, wild sauerkraut is just cabbage chopped up with salt, cultured sauerkraut is (sterilized or not) cabbage, salt and some sort of starter culture like whey or a commercial product made just for this purpose.  These seed cultures are awesome sometimes.  For example, if you left some milk out on the counter, you get sour milk (or worse), but add some Fil Mjolk and you get a tasty yoghurt.  The other advantage of using a starter culture is it provides a more consistent result between batches, whereas wild cultures has more variation.  I'm going to assume we are talking about wild ferments unless otherwise specified.

Open vat fermentations are basically a wide mouth container, some veg, some salt, some water, and possibly a starter culture.  The veg are weighed down with an inner lid and a weight like a rock or bottle of water and covered with a towel to keep out flies and dust.  The inner lid and weight insures that all the veg stay below the level of the brine, and thus out of contact with the air during the fermentation.

The top of the brine, however, is exposed to the air.  Sure there is a slight layer of CO2 gas (fermentation farts) that settle on the undisturbed brine, which protects against some O2 (oxygen) contact, but how well it works is limited.


Airlock ferments have basically the same contents as the open vat, only an extra stage is taken to prevent the surface of the brine from touching oxygen.  This will be something that allows the ferment farts (CO2) to escape without letting any gas back in.  The Pickl-It system is the best example of this, but some people use those snap jars with the rubber rings like this one:

This is the type of airlock often used on alcohol

So long as it lets the ferment farts escape, prevents air from entering the container and won't explode from the gas buildup, I'm going to consider it an airlock system in this post.

With the airlock system, the fermenting veggies must be kept submerged beneath the brine just like the open vat system.

In my opinion, the best use for an airlock system does is when the contents of the ferment have been sterilized, neutralizing or killing the wild bacteria, then given a starter culture to it.  This way, it prevents any wild contamination from entering the vat.



Before we really get into this, I want to let you know a bit about my approach.  As a former academic I've read and understood a large amount of the scientific literature on this topic.  I also know and understand the technical jargon, I just choose not to use it when writing this blog.  What's the point in showing off my big words?  That would restrict my audience and intimidate people new to the idea of fermenting.  Big, technical words are awesome when I want to show off how smart I am, that I'm paying attention, or when I need to be very specific.  However, they have a time and place and if a person cannot put the idea into lay terms, then quite frankly they don't understand it.

Have I mentioned I'm also opinionated?

My idea in writing this is not that everyone should convert to my point of view.  It's more in response to one extremely vocal side of the fermenting community.  They quote science and lovely fancy words to browbeat people into their way of thinking - or what happens more often, to browbeat others into giving up entirely on fermenting.  I don't think they realize what they are doing because in their heart of hearts, they feel they are doing good by spreading the gospel of airlocked fermentation.  Perhaps they don't realize that the expectation of everyone achieving perfection on the first attempt is a bit intimidating (I put that way nicer than I feel about it - but hey, I do respect them as knowledgeable and enthusiastic individuals, and I want to give them a fair hearing).

I can find nothing wrong with the science they cite; however, the idea that all fermentation must be in an airtight condition otherwise you don't do any good for your health or possibly damage it, is based on some rather dodgy premises.  If we accept their assumptions (starting premises) then their conclusion is sound (has a logical structure and is relevant to reality).  I have some doubts as to just how much evidence there is in the world to accept these assumptions.  That's what I want to talk about today - not the science it'self, but the philosophy that underlies it.

The other goal of this is to reassure people just starting out with fermenting their own foods that they don't need specialized equipment or knowledge.  All that sciency stuff and toys can come later, for now ignore the neigh sayers and those who bully with good intentions, and just get started.




So basically, both the airlock and open vat systems protect the veg from contact with the air.  Why do we need this?  In a really oversimplified way, there are invisible beasties interacting with the veg to preserve it and make a nice sour flavour.  These invisible beasties are good for your digestion, in fact it's like they are pre-digesting some of the food before you even pop it in your mouth.  I'm going to assume here that you've seen enough yoghurt commercials to know that probiotics are good things to eat.

These invisible beasties, the ones we want, live in an environment that doesn't like oxygen, thus we keep it submerged in brine.  If we left it out in the air, different invisible beasties would start acting on the veg and turn it to unappetizing mush (compost).  By controlling the environment, we influence which invisible beasties (which include yeast, bacteria, fungus and other things) are dominant.



The airlock school of thought has some great science that talks about how many more good bacteria an airlock system can produce and how that the part of the brine that has exposure to O2 reduces the amount of these specific bacteria and grows air-friendly invisible beasties.

I've read the science, I'm not disputing any of it.  It's good science!

However, it does rely on a few assumptions.

1. exposure to all air bacteria (aerobic) is harmful to us
2. if some anaerobic (living without air) bacteria (invisible beasties) for us is good, then way more of it is better
• this also assumes that our body has an unlimited ability to use these bacteria.
3. That it is only the anaerobic bacteria that is good for us.
4. It is only the quantity of the bacteria that is good for us, not the ratio.

The first assumption is crucial to the point of view that we should always use an airlock.  It's also the most pathetic assumption.

Think about it, we are exposed to aerobic bacteria (air loving invisible beasties) constantly.  We breath it, we touch it, we eat it on our food... Some of them harm us, but not all of them.  Some of them help us, but not all of them.  We don't understand everything about the invisible world, but we do understand that without air loving invisible beasties, we wouldn't exist.  Therefore, it's difficult to accept the first premise.  Not all aerobic bacteria (air loving invisible beasties) are bad for us.

So is the way that the air loving invisible beasties interact with the ferment bad for us?  Well, it reduces the non-air loving invisible beasties and over time will slow and changes the ferment... But is that entirely bad?  Most people these days ferment for taste and don't leave the vat of sauerkraut at room temperature for a year before chowing down.  They make smaller batches, fermented for shorter periods of time and consumed within a few weeks or months.    So the good/badness of the air-ferment interaction does not factor into it nearly so much as it would for longer fermentations.

But also, how do we know that this air-ferment interaction is bad for us as eaters?  Just because it reduces the quantity of the non-air loving bacteria, does it follow with absolute certainty that it is bad for us (in moderation like you find in an open vat system)?  More on this follows.

The second assumption, if some is good for us, then more is better is a common belief in this day and age, however, it's usually faulty.  Actually, scratch that, it's always faulty.

An example: water is good for you.  In fact, like bacteria, it is necessary for your survival.  Too much water is deadly.  You are probably aware that you can drown in too much water, but did you know that if you drink too much, it will kill you?

Another example:  Oxygen.  We like this.  It makes us stay alive and breath and stuff.  But too much oxygen, and you get sick and/or die.

That's some anecdotal evidence showing that if a little of something is good, then more of it isn't always better.  Bringing it back to the fermenting topic - yes, everyone agrees that some non-air-loving invisible beasties (anaerobic bacteria) is good for you.  It's a probiotic that improves gut health and digestion.

However, if some is good for you, what evidence that more is better?  Where is the line drawn?

One of the problems with this is that bacteria often competes with each other for food and space, often changing the environment to suit it's needs and exclude competition.  We know that the body needs a balanced bacterial community to function properly, but consuming a lot of one bacteria (or one conglomeration of bacteria), we risk tipping the balance in our gut.  But eating some is good, too much is bad... hmmm.

That brings us to the sub-premise (the little bullet point beneath the second assumption), that our body has the capacity to use all the bacteria.

We know that it can use some bacteria, and that too much of a limited kind of bacteria is harmful.  But the real question is that if we can use all the extra anaerobic bacteria (non-air-loving) produced in the airlock ferment.

The airlock produced a lot more of this friendly bacteria than the open vat system (no one is disputing that), but can we use it?  Even if it isn't harmful, is it helpful to have that much more?  Is it like Vitamin C, the body uses so much and flushes the rest out, therefore it's useless to take extra - is it like that?  Is going to the extra effort of culturing more anaerobic bacteria worth it, or does the law of diminishing returns apply?

The third assumption, that only anaerobic (not-air-loving) bacteria is good for us to consume.  This is only subily different from the first assumption, so I'm not going into detail in the interst of brevity (3 thousand words is enough for one blog entry don't you think?). - this is pretty much addressed when I talked about the first assumption.  But to recap, it's obvious that this is not true.

The fourth assumption, that it is the quantity of specific bacterial species which is important and not the ratios.  This is so very 20th Century, and I don't blame people for thinking this.  I disagree with it, but sciencey people come by it honestly, they were trained to focus on one factor, item, or collection of similar items, because it's easy to isolate for all the variables.

However, these days, people are starting to realize that isolating one variable does not lead to the ability to predict how the entire system works.  For those who studied philosophy at university, the fallacy label goes like, 'assuming that the whole is the sum of it's parts'.

Even if we were able to isolate and study each individual bacterial species on it's own, especially the ones that interact with our digestion, we still wouldn't be able to understand the entirety of how our gut works.

When it comes to the health of the human body, more and more people are beginning to realize that it's not the individual components, but rather the ratios between them.

We can take this to refer to the ratio of anaerobic (not-air-loving) bacteria in our gut talked about earlier, but we can also look at the ratio of anaerobic and aerobic bacteria (air and non-air loving invisible beasties) in the ferment itself.

Wait!  Am I suggesting that the air contamination that happens with the open vat system may actually be a good thing?  Sort-of.  It's more something I've been wondering about and have failed to find any studies into it that both look at the interaction of the air and non-air loving bacteria in the vat AND how this ratio interacts with the human gut.

But why would I even consider this a possibility?  Let me tell you.

I am slightly obsessed with the history of food and food preservation pre-refrigeration.  Lacto-fermentation - the fancy name for what happens when you make sauerkraut and what we've been talking about this entire post - ... Lacto-fermentation has been used by people for a few thousand (probably a few ten-thousand) years, and during this time, it was almost always in an open vat kind of system.  The 'airlocks' available until the 19th Century, were slightly porous, which allowed the food to breath.  For example a bladder (pre-20th Century clear-wrap) is very slightly porous and over time, 'breaths'.

So I look at history and I see that for most of human history people have been using open vat fermentation with out any obvious ill effects.  Especially none of the ill effects that some of the more enthusiastic pro-airlock followers declare will happen.

Looking at what we are learning about ecosystems (because what is a gut full of invisible beasties if not an ecosystem? - rhetorical question), human health, and history, it makes me wonder if looking only at the quantities is missing out on the really important aspect of fermenting (and how it relates to our health).  Maybe there could be something to the ratios of invisible beasties - and possibly, just possibly, maybe using an airlock is detrimental to our health.  This needs more study.



One day, these assumptions will be taken into account, and I could well be proven wrong about them all.  But until that time, there isn't enough foundation to believe that an airlock is completely necessary.  The arguments of the pro-airlock school is logical (it makes sense to the rational mind) but it has yet to be proven that it is sound (the assumptions at the beginning of the argument have yet to be found without question to be relevant to reality).

My opinions on the topic of using an airlock or not when fermenting:

First of all, please stop pounding beginners over the head about being perfect.  Even if the airlock is the best way to go, it's not the only way that works.  Give them a chance to try making some kimchi with the materials they  have on hand and get excited about fermenting.  Once they are excited, then you can bombard them with your opinion on how to do it right.  But please, not before.

I use an airlock when it suits me, and I don't when it does not.  More importantly I don't care what you use when you ferment.  It's YOUR choice, not mine.  Do what you want.  In complete and brutal honesty - I DO NOT CARE what you use.

What bothers me is this new kind of cyber bullying that comes from people trying to help by expressing their opinion that the only way to do something is the right way and that if you can't do it that way from the start, don't even bother.  Yes, people go to forums looking for answers to their questions, but the reason they are really there is to seek support and fuel their enthusiasm for their new hobby.  The line between being helpful and being a bully seems to be getting thinner as time goes on.  But I can give you an example of what the difference looks like (roughly paraphrased from things I've seen in different places on the internet)

N00B: Oh wow, I'm so excited to start my first kimchi.  The only thing I have on hand is this plastic tub, a cabbage and some salt.  What sort of thing should I use for an inner lid?

Helpful:  Good for you starting your first kimchi, let us know how it goes and feel free to ask if you run into any trouble.  I usually use a plate for the inner lid, but some people use plastic or wood or any non-reactive thing that fits.  Maybe later on, you might want to move away from plastic as some people believe it can leach into your food.

Bully: Don't use plastic ever!  That's so nasty.  Just toss it out.  (technical stuff about molecules leaching... acid reaction...&c.).  What you really need is this expensive fermentation vessel and starter culture, because you just can't rely on wild bacteria.

Did anyone notice how the Bully answer usually doesn't answer the original question?  Anyway, enough of my complaining.  You get the general idea of what motivated me to write such a long post.


I wonder if all this talk about airlocks and stuff isn't some residual meme leftover from the public education system.  All that fear of botulism and other possible harms that come from an industrial food system but are not present in a fermented setting, these fears linger and are difficult to shake.  Maybe this is what drives people to take total control of the fermentation - with airlocks and starter cultures and total sterilization at every step in between.

For those of you on the receiving end of those well meaning lectures as to why you must only ever always use an airlock when fermenting.  Be strong.  These people have a lot of science and aren't afraid to use it.  They are also very intelligent and vocal.  It's hard to stand against that, especially when all you have is an unarticulated feeling in your gut that maybe something they say isn't right, but you can't find any fault in their logic or science.  That's mostly because there isn't any fault in their logic or science.  It's their basic assumptions that have yet to be proven... and if you want to argue that, it's near enough futile.

Arguing basic assumptions with a passionate, intelligent person results in cross monologues.  Which is to say, you both yell at each other and cannot hear what the other is saying, so really you're just yelling at yourself, and that's not something a sane person should be doing in public (on the street or in an internet forum - both are public, the latter more than the first).


Check out this interesting discussion about fermenting with airlocks and open vats