When we discuss oxygen in a ferment, we aren’t talking about the bubbles you see in your ferments- that is carbon dioxide off-gassing from the bacteria. We’ll discuss those fun bubbles another day.
Oxygen in water is dissolved. That means you can’t see it. But that’s good because if it wasn’t dissolved, the fish and other sea creatures couldn’t use it. It has to be dissolved in the water for their gills to grab it.
Three Routes For Oxygen
There are three ways oxygen can get into water. Diffusion, aeration and from plants off-gassing.
Aeration is really just diffusion that gets help from movement. It is where water get stirred or churned up such as rapids, waterfalls and waves. This gives more surface area for water to be exposed to the air so it can uptake more oxygen. This applies to fermentation only if you’re disturbing your ferment regularly by stirring it. Or as what happened to me once, my three-year old got ahold of it and shook it to see ‘all the pretty bubbles.’
Off-gassing from plants is the same that happens on land. Plants produce oxygen from photosynthesis underwater just like they produce oxygen on dry ground. But there aren’t enough plants in the sea to aerate all of the water and this only occurs in the presence of light, since sunlight is required for photosynthesis. Off-gassing isn’t a big issue in veggie fermentation, either, as by the time you’ve started fermentation, the plant’s cellular respiration has drastically slowed down. AND you should be fermenting in the dark as some LABs are light sensitive, as is Vitamin C.
Diffusion is the important part of this discussion. Just as on dry land, there is a concentration gradient (sometimes called molecular diffusion) that always pushes things from areas of higher concentration to lower concentration. Remember in elementary school you watched food coloring swirl around in a glass to distribute itself without you shaking it? That’s the concentration gradient working.
So if you’re fermenting in a way that provides the brine with an oxygen source, as the bacteria use up the oxygen, more oxygen is just going to keep diffusing into the brine because it’s always going to work on the principle of a concentration gradient. If you’e ever heard the term ‘atmospheric pressure,’ this is what is responsible for pushing the oxygen into the water. The more atmospheric pressure, the faster the oxygen will diffuse into the water. The percentage of salt you’ve used to make the brine also helps determine how much oxygen the water can hold- the less salt, the more oxygen it can handle. Temperature also has an effect.
In case you never did the food coloring experiment, you’re familiar with diffusion even if you aren’t a science buff. It’s how smell moves through the air. That’s how you can smell dinner cooking when you walk in the front door, before you make it to the kitchen. The molecules are moving from areas of high concentration (the kitchen and around the cooking food) to an area of lower concentration (the living room, out the kitchen window, down the hall…). It’s the same principle, it just happens at different rates depending on a couple of factors- salinity and temperature.
KerryAnn, How Much Are We REALLY Talking About?
I can hear someone saying now, ‘but it can’t be much oxygen!’ That’s right, it doesn’t happen overnight. It’s just enough to keep those aerobic bacteria alive so they can spoil a ferment and set up the environment for mold on a self-brining ferment. In other words, it’s enough to wreck your ferment.
First off, let me point out that microbiologists and food scientists strategically use oxygen in a lab to promote the death of some types of LABs that are being grown in an anaerobic environment. And it requires lab equipment to exert that level of control and you’re not going to be able to achieve that in your kitchen, so this isn’t an argument for exposing your ferments to air, it’s an argument against it. When you don’t have equipment that exerts the anaerobic control, the bottom line is that you have no control. That’s important to note and we’ll elaborate on that another day.
Diffusion takes place at the rate of about 1 meter per year or 17 days for every inch, give or take, for fresh pond water. Studies have shown that it’s about 25% slower in the Dead Sea than in distilled water, which is 31.5% salinity. Most of what you ferment, you’re aiming for a 2% salinity, so we’ll go with the 17 days per inch figure since it’s likely close to that.
Then you have to take temperature into account. Back in the 50s, a study answered the question of diffusion rates and temperature for various liquids and studies today all pretty much point back to that paper, so we’ll go with that. So, looking at that information and the temperatures you should be keeping your ferments at versus the likely temperature of pond water, you can expect that it would take place about 17% slower in the fridge over the temp of pond water used above. That puts moves us from 17 days per inch to just under 20 days per inch. So we’ll go with 20 to make the math easy.
If you bug your ferment continuously as many are apt to do (more on that below), the oxygen would be able to permeate the top 3.5 inches of the brine by ten weeks. That’s 70 days divided by 20 days per inch = 3.5 inches of penetration. That’s a conservative figure because I’m figuring it all at storage temperature, as oxygen does diffuse faster the first 3-10 days while you’ve still got it on the counter.
So what’s the bottom line? In a mason jar, if you are making kraut and you only bring the brine to the shoulder so you have room for expansion,that’s about three-quarters of the quart jar before you’ve had a chance to consume any!
What if my numbers are off? OK, if that’s wrong and I’m off by 25%, you’re still looking at over half the jar by the ten week mark. But if I’m really wrong, you’re still looking at a portion of the jar. And it’s the portion you’ll be eating each time when you open that jar.
What a Crock
Now, the above obviously applies to open crock fermentation.
With systems that create pressure but are’t airtight (read: everything except a Harsch or Pickl-It), the rate of diffusion will not be an issue for the amount of time the pressure is outward- when carbon dioxide bubbles are being actively released. But once active fermentation ends and the pressure equalizes, you’re right back to the diffusion issue. So having a lid helps slow it down but it doesn’t stop the problem of oxygen being diffused into your ferment completely.
Since most people let the jar sit in the fridge for a while before consuming it because they don’t like how salty it is, that makes for even more diffusion. In fact, how often do you hear people say if you don’t like how salty your ferment is, just check it regularly for a couple of months? I know I’ve heard that advice many times and I’ve even given it myself a time or two! Unfortunately, while that advice is correct in that the saltiness will reduce (because the bacteria consume it), the oxygen will increase if your container isn’t airtight, thus reducing the anaerobic bacteria and making your ferment less beneficial, AND feeding the bad, oxygen living bacteria at the same time.
By now you should hear the dozens of mason jar fermenters who have been sending me angry letters yelling, ‘but carbon dioxide is heavier than air and that seals it!’ Yes, that does come into play. However, it isn’t a ‘seal’ and that layer of carbon dioxide doesn’t fix the problem due to poor but commonly given fermenting advice.
It seems I meet few people who haven’t been taught to fiddle with their ferment regularly if not daily. Taste it, open it, poke around, mess with it, play in it. The common advice is to taste it daily and obsessively repack it. You just don’t commonly see the advice to walk away and leave it alone unless there’s an obvious reason to intervene, such as the fluid being able to push out the airlock or to re-secure items floating on top of the brine. In fact, this week I had a woman insist that opening a jar and fiddling with it daily was absolutely necessary for a ferment to turn out correctly, as if all bacteria NEEDED her intervention and direction in order to survive.
Human nature for most people is that they won’t leave well enough alone and trust that the process doesn’t need their constant ‘improvement’ and intervention to turn out right. Well, that advice hasn’t turned out well in birth, modern medicine or just about ANY other avenue I can think of. Fermentation is no different.
Then, once the ferment is ‘right,’ you’re opening the jar to get a little out two or three meals a day, you’re constantly disturbing that carbon dioxide layer and once it’s gone, the off-gassing has slowed down to the point that it’s not going to build back up quickly or well, otherwise your jar would still be pressurized.
So, yeah, that carbon dioxide argument likely isn’t as sound as they had hoped.
Want that carbon dioxide to work in your favor and be an ally? Quit fiddling with your ferment! If you need sensory therapy, please get it elsewhere. Only open the container when absolutely necessary and try to disturb it as little as possible.
Another issue to note is that salt and carbon dioxide aren’t really compatible. Too much salt can drive carbon dioxide out of a ferment and putting too much salt in your ferment can also be counter-productive for this reason. If you drive it out too quickly, you can’t rely on that layer of protection in the same way.
You see, bacteria naturally congregate in areas that are most favorable for their survival. This handy, dandy picture even show you what it looks like so you better understand. If you read the description, you see #2 shows all of the oxygen hating bacteria would be gathered at the bottom, away from the surface. The ones who can stand oxygen but don’t have to use it would be distributed throughout, which is tube #3. And, of course, in tube #1 you see the oxygen-loving, aerobic bacteria will gather at the top.
So every time you get some out of the container, you’re picking up the portion on the top that is more likely to have the oxygen-loving bacteria which potentially have negative health effects and definitely have the potential to spoil your ferment. Then you’re exposing what’s left to oxygen, dissipating the layer of carbon dioxide that developed, the brine drops, diffusion continues. More of the anaerobic bacteria die off and those that survive migrate father down into the bottom of the jar, away from your reach. Stirring the jar isn’t the answer, it just creates more problems!
By the time the jar is only half full, the bacteria present can’t completely use up the oxygen between openings even in an airtight system (hence the advice I gave previously to move your ferments to a smaller Pickl-It or airtight jar once you’ve used up half of the contents), so if you’re using a system that isn’t airtight, it really has a strong effect.
In an airtight system such as a Harsch or a Pickl-It, the lactic acid bacteria are distributed throughout the ferment and they aren’t competing with the oxygen loving bacteria. So, once again, we see that the Harsch and the Pickl-It are comparable and mason jars and open crocks are in a different category.
Eyes on the Prize
So even if you have your lid screwed on your jar, if you aren’t fermenting in an airtight container, you’re getting some diffusion and encouraging the oxygen-loving bacteria. The oxygen that gets in will diffuse into the brine. And when you consume those ferments, you’re getting primarily the oxygen-loving bacteria and less of the LABs you want.
We should ALWAYS keep our eyes on the prize. The goal of fermentation is to produce the maximum amount and a wide variety of lactic acid bacteria while killing off all of the oxygen-happy bacteria that either won’t benefit you or will harm your gut while spoiling your ferment in the process.
You see, there is only so much space and so much food for these bacteria. So you don’t want to encourage the bacteria that won’t benefit you from hanging around, you want them gone.
I don’t want to eat ferments that are on their way to spoiling. We’re not talking the same way we talk about produce. ‘Beat the clock’ isn’t a beneficial game when it comes to this. You want your ferments preserved for the long-haul, so they’re rich in many types of lactic acid bacteria. You don’t want to eat something on the downward slide.
And, yes, I want the maximum amount of probiotics. That’s why I’m fermenting in the first place!
So once again in this series, we see that the mason jar and the Pickl-It aren’t competitors. We see that the Pickl-It and the Harsch produce one type of ferment with a particular bacterial profile, and we see other methods produce a different type of product with a different bacterial profile, and even among those the bacteria types and numbers can be different.
How much loss is acceptable to you, especially if you’re trying to heal your gut or fix a health issue?
I’ve met a number of folks whose health stalled until they switched from fermenting in a mason jar to a Harsch or a Pickl-It. Could it be that the lack of anaerobic bacteria in their ferments was to blame? If your improvements have stalled, perhaps this might be a piece of the puzzle for you?
I’m finding very much that this issue is part of the answer for me and why I didn’t improve as I should have while using a mason jar. And when I made the switch, I saw health gains on things I didn’t think were related to the issue of consuming ferments. When I switched to the Harsch to the Pickl-It, I saw more gains simply because I starting eating more ferments on a regular basis instead of only eating a little sauerkraut at dinner daily. Being able to eat a variety of ferments all the time instead of the same thing every time encouraged me to eat more in volume.
While using mason jar ferments and following the common advice, I still had to take large doses of digestive enzymes and multiple probiotic pills to get better. That’s insane, as a good ferment should produce far more beneficial bactera than the probiotic pills contain and should contain a wide array of digestive enzymes. But it didn’t work for me.
Perhaps had the Pickl-It been available at the time, I might have saved a ton of money (I spent hundreds on supplements a month at my worst) and sped up my healing. We’ll never know the answer to that question. But seeing other people have health gains using anaerobic ferments after stalling with the commonly heard fermenting advice coupled with my own recent experience makes me think there’s something to it for at least a segment of the population. It makes me think there’s something specific about some of the anaerobic bacteria that is a key to healing in some people.
I’ll be posting more about these issues soon.
Science Aside… Will They Eat It?
One other issue that bears mentioning here is flavor. The final flavor profile of a ferment is determined by the types and amounts of bacteria present. Also, anaerobic ferments don’t gradually loose their crunch over time as aerobic ferments do. My kids won’t touch ferments with even a hint of mush, so it’s a waste of time and money to make it any other way. I’ll do more digging and we’ll return to the flavor issue another day.
Ferment in a sealed, anaerobic environment where the bacteria can use up the oxygen and then the LABs can out-compete the aerobic bacteria, killing them off. The Harsch crock or a Pickl-It are the two means I know of currently that are truly airtight.
Want to read more about fermentation, including articles with references and more information on vessel types? See our Related Posts for all of the articles in this series.