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Unlike many of my colleagues, I don't have a single pet. I have billions of them. I'm not joking. I provide for them by feeding them and giving them a comfortable home where they can thrive. As with most pets, I have to put up with their incessant and uninhibited eruptions of gas, but it's more than worth it for the unconditional love I get from them in return. In my case, that love comes in the form of sauerkraut.
My pets, if you haven't already figured it out, are the billions of lactobacillus bacteria that have been camping out in crocks and jars on my countertop for the past several weeks. They've been eating the shredded cabbage's natural sugar and converting it into lactic acid and carbon dioxide (hence all that gas). As the lactic acid builds up, the kraut gets increasingly sour, gradually developing into the stuff we love to heap on hot dogs and alongside brats.
I've been fermenting foods at home for several years now, from kraut to carrots and cucumbers to hot sauce, and it remains one of my favorite cooking activities. We write a lot about the science of cooking on this site, though most of that is focused on the chemical and physical processes that happen when we do things like salt and heat our foods. Fermentation gets you knee-deep in the biological sciences, and it's a fun place to be. No longer are you cooking alone—instead, you're teaming up with an army of friendly microbes, working in tandem to transform and preserve fruits and vegetables. It's something humans have been doing for millennia, and if you haven't tried it yet, it's time you start. I mean, who doesn't want to be the master of their own microbial universe?
When we make something like sauerkraut, what we're really doing is pickling. But it's not just any pickling: It's pickling by way of fermentation specifically. This is different from the process of making so-called "quick pickles," like these, in which a brine made from an acid like vinegar is used to flavor and preserve fresh or par-cooked vegetables. Because of vinegar's inherent acidity, those vegetables are preserved right away as microbial activity grinds to a halt. (Sugar and salt in the brine also help stop the little critters from surviving.)
With fermented pickles, you don't add an acid directly to the vegetables. Instead, you let a specific kind of acid-producing bacteria—lactobacillus, in the case of sauerkraut—run wild. Given the right conditions, which I'll explain below, they'll do all the work to create the acid for you. This is true of sauerkraut ("sour cabbage" in German), which is pickled shredded cabbage, but it's equally true of sour dill pickles, kimchi, and even some hot sauces, in which the chili peppers are fermented and then blended to form a smooth sauce. (Tabasco, in case you're curious, is one example of a fermented hot sauce.)
Kraut is one of the best starting points for trying your hand at fermentation because it's one of the simplest, since you can make it with nothing more than cabbage and salt. Once you get the hang of it, it's not much of a leap to try pickles, like kimchi, that include a larger number of ingredients.
How It Works: Sprinkle the Salt, Hold the Oxygen
Lactobacillus bacteria are everywhere. They're on our skin, in our bodies, and on the fruits and vegetables we buy and eat. They're generally considered to be "friendly" bacteria, meaning they aren't harmful to human health and may even be beneficial in some cases.* Some companies sell starter cultures of lactobacillus, which you can add to the crock to help kick off fermentation, but in my experience, this isn't necessary—there's more than enough naturally occurring lactobacillus in our environment, so you don't need to augment it with special products.
* Exactly how beneficial, from what I understand, remains an unresolved question in the dietary sciences, so I won't speculate much on it here. Lactobacillus-rich foods may do your body some good, or they may not.
Lactobacillus has two important qualities: It can survive in oxygen-free environments, and it can tolerate salt better than many other microorganisms. It's these two qualities that we exploit to successfully ferment vegetables, like cabbage in kraut.
First, we add enough salt to make life difficult for competing microorganisms. If this were a football league, it'd be like putting liquid heat in the jockstraps of all the players, except the ones on the team we want to win. When it comes to kraut, a level playing field is not what we're after. This salty environment is just dandy for the lactobacillus, though, paving the way for its total domination over other bacteria.
While there isn't full agreement among pickling experts about the perfect amount of salt for the fermentation of sauerkraut, the general rule of thumb is about 2% by weight. That means that for a small, three-pound head of green cabbage, you'd add one ounce of salt. In the metric system, which makes these kinds of calculations much easier, that same head of cabbage weighs about 1,400 grams, and therefore would need 28 grams of salt. Using Diamond Crystal kosher salt, our preferred brand, that comes out to just about three tablespoons for the three-pound head of cabbage. Put another way, that's about one tablespoon of Diamond Crystal kosher salt per pound of cabbage. Please do not make the mistake of using the same volume with other types and brands of salt, as their densities vary—for this reason, weight is by far the more reliable method of measuring. I recommend grabbing a small gram scale to accurately weigh these small quantities.
The salt has an important second role: It draws moisture out of the cabbage's cells through osmosis, forming a salty brine. Because the cabbage is shredded, its surface area is maximized, meaning that a surprising amount of brine can accumulate even from a juice-free vegetable like cabbage. With the help of some mechanical bruising through kneading and squeezing the cabbage, its cells break down even more, speeding up the release of liquid.
This brine brings us to the second important quality of lactobacillus—its ability to survive in oxygen-free environments. When we submerge the cabbage in its own brine, the lactobacillus and other microorganisms living on it are deprived of oxygen. Many will die as a result, but lactobacillus kicks into anaerobic (oxygen-free) fermentation mode, converting the cabbage's sugars into lactic acid while creating by-products like carbon dioxide. You'll know that fermentation is under way when your cabbage starts bubbling and burping.
The main enemy throughout is oxygen, which is why you want to keep your cabbage submerged in the brine the whole time. Sometimes molds can form on the surface of the brine, especially in the early stages, when the cabbage hasn't fully acidified yet; mold on the surface isn't ideal, but it's not a sign that your kraut needs to go in the trash, either. Just carefully scrape it off and proceed as normal. Still, with the help of an airlock, which I'll describe below, you can reduce the chances of mold forming.
To judge the success of your kraut, your eyes and nose are your best tools. If everything looks okay, and if everything smells okay, everything is okay. What is "okay"? A nice, even color throughout, turning beige and even lightly golden in the later stages, and a pleasantly, lightly funky smell that's a bit sulfurous but otherwise clean. The cabbage will soften somewhat throughout the process, but it should retain a squeaky, crisp bite, without any sliminess. (And yes, you can taste it along the way to follow its progress.)
One of the best things about making sauerkraut at home is that it doesn't require much equipment. All you need is a nonreactive crock or vessel that's relatively narrow and tall—the less surface area exposed to air, the better, and the easier it is to keep the cabbage below the brine.
I've used swing-top glass canning jars before with good results, but while recipe-testing for this story, I tried out a few other devices and have a couple new favorites.
If you plan on making large batches of sauerkraut and other pickles, it's worth investing in a real ceramic fermentation crock. I bought a five-liter German-style crock, which comes with stone weights to hold the cabbage down, and was able to easily fit eight pounds of cabbage in it—that's a lot of kraut. I actually could have packed in another four pounds, while still leaving enough room for things to bubble up without overflowing.
The crock has a couple other advantages, aside from its size and the included weights. First, the ceramic keeps things nice and dark in there, which is good, since light can degrade food over time. Second, it has a water lock for the lid to sit in: Slot the lid into the channel around the crock's opening, then fill it with water, and it will let air bubble out but not back in. This functions as an airlock, allowing the carbon dioxide to fill up the air space in the crock, and eventually escape, without letting any oxygen-rich air back in. The result is reduced likelihood of mold forming inside. As with any airlock, if you open the vessel up, you'll break the seal and let oxygen back in; that's okay, but keep in mind that the mold risk increases the more you do it.
The downside of a large crock is that, well, it's big, and it requires ample storage space. If you're not ready for that kind of commitment, I'd recommend fermenting in half-gallon Mason or Ball jars instead. They're smaller, but also more versatile, since they're useful for holding plenty of things besides fermented foods.
It's possible to use the Mason jar with its own lid, burping it occasionally to prevent too much pressure from building up, but I like the ease of specialty lids designed for fermenting. They have airlocks or valves built in, allowing gas to escape while preventing oxygen from seeping back in.
Of the kinds I tested, I most liked the Easy Fermenter. It has a slim profile, thanks to a basic rubber valve instead of a bulkier three-piece fermentation airlock, making storage easy. It also has a dial on its surface, with numbers that correspond to the days in a month: Set the dial to the day you start the ferment, and you won't forget later just how many weeks it's been going. (This is especially helpful if you plan on fermenting lots of things and risk losing track of when each one started.)
The last bit of gear that I found helpful when using Mason jars was glass fermentation weights. Again, they're not required, since there are a lot of ways to weigh down the cabbage, but these glass ones fit the jars well and are easy to clean and store. Otherwise, you'll be forced to rig up your own system for compressing the cabbage, which—I can tell you from experience—doesn't always work as well as you hope.
Whatever equipment you decide to use, once you have it, it's time to get fermenting.
Making Sauerkraut: Step by Step
Step 1: Weigh, Then Shred Cabbage
Start out with nice, tight heads of green cabbage. Weigh the cabbage, then calculate the amount of salt you'll need based on that. You want 2% salt by weight, so 20 grams of salt for every kilogram of cabbage, or roughly one tablespoon of Diamond Crystal kosher salt per pound of cabbage.
Trim and core the cabbage, removing the outermost leaves. (You can discard these, or save them to help hold the shredded cabbage down in the crock later.) Then shred the cabbage, either by hand or using a mandoline or a food processor with its slicing-disk attachment.
Step 2: Add Salt and Spices, Knead, and Squeeze
If you're using a large ceramic fermentation crock, you can add the shredded cabbage directly to it, sprinkling the salt on and mixing it in intermittently as you fill it up. If you're using a glass Mason jar, start with the cabbage in a large mixing bowl, sprinkling it with the salt and mixing it well.
Squeeze and knead the cabbage for a few minutes to begin drawing out its liquid, letting it stand in between; I like to cover it while it stands, either with the lid of the crock or with plastic wrap, to prevent the precious brine from evaporating. Every 15 minutes or so, come back and squeeze and knead the cabbage again, helping to release more and more brine.
Exactly how long this will take and how much brine you get will depend on the cabbage you have, but after anywhere from one to four hours, you should have a decent amount of brine built up—enough to cover the cabbage when it's compressed.
You can also mix in spices now, like caraway seeds, for a more German-style kraut, or juniper, for a more Alsatian style.
If you're using a Mason jar, now's the time to transfer the cabbage and its brine to the jar. Try not to pack the jars or crock more than two-thirds full, since the contents tend to bubble up during fermentation. If the vessels are too full, they may overflow.
Step 3: Weight It Down
Push down on the cabbage to compress it; this should force the brine up. If you're lucky, there will be enough to cover the cabbage by about an inch or so. If not, you'll need to make some extra brine (which we'll do in the next step). If you saved those outer cabbage leaves, you can lay them across the top of the shredded cabbage and use the weights on top of that—they can help keep little shreds from sneaking up above the weights. Just make sure all the cabbage, including those leaves, is below the brine.
Step 4: Add Extra Brine, if Necessary
If you don't have enough natural brine from the cabbage to cover it well, you'll need to top it up. It's important that the brine you use maintain the same 2% salinity as the cabbage and its brine. To make it, fill a measuring cup with water, and calculate the salt weight based on that—for every 100 grams of water, you'll want to add two grams of salt. Now add this saltwater brine to the vessel until the cabbage is well covered.
Some people claim that fluoridated tap water can't be used for fermentation brines, but I've never had a problem. While fluoride may inhibit microbes to some degree, I haven't found it to be a real impediment to fermentation, at least not with the tap water I use in New York City.
Step 5: Seal and Store in a Cool, Dark Place
Seal your fermenter following its instructions, and keep it in a cool, dark place. Temperature has an effect on fermentation, encouraging some types of bacteria to flourish and others to go dormant. You have some wiggle room here, but somewhere around 65 to 70°F (18 to 21°C) is good for sauerkraut.
Because light can degrade foods over time, as mentioned above, keeping your vessels—especially clear glass ones—in the shade or dark is best.
Step 6: Wait, Then Eat
Now you just have to wait. After a day or two—or three—your kraut should start bubbling and fizzing as the lactobacillus becomes the dominant microbe and starts to plow through the sugars. If your vessel is pretty full, you may want to set it on a rimmed tray, just in case it does bubble over. This is when it will become clear that you have something alive on your hands—a little microbial universe in which you are god.
After a week or so, once the first big push of fermentation has settled down, feel free to open up your crock and sneak a taste. (While also keeping in mind that opening and closing the sealed container increases the chances of molds and such forming—wash your hands and utensils before sticking them in!) If mold does grow on the surface, just carefully skim it off. As god of your kraut, you have a right and a duty to tend to things.
If the cabbage rises above the brine, go ahead and push it back down; if the brine ever seems too low, just make more brine following the same 2% salinity formula, and top it up.
After about three weeks, your sauerkraut should be pretty far along, quite sour to the taste. You can let it go another few weeks, up to about six or so. At that point, it's a good idea to transfer it to the fridge, where the cold temperatures (combined with the high acidity) will slow any remaining fermentation to a near-standstill.
The kraut will keep for many months in the fridge at this point. If I'm being honest, I've kept some for more than a year. It eventually loses its sparkle and starts to taste dull and old; at that point, it's probably not worth the risk of attempting to eat it, even if that risk is minimal.
When it's all done, it definitely stops feeling like you have a billion pets and starts feeling like you have a lot of delicious fermented cabbage on your hands. It's time to make some sausages, grill some hot dogs, or cook up some choucroute. And then recruit your next army of loyal bacteria. There's a lot of cabbage waiting to be preserved.