Real Sauerkraut in a Jar: A Beginner's Guide to Fermenting Cabbage

If you have more cabbage than you can eat before it turns, fermenting it is one of the oldest and simplest ways to put it by. No heat, no boiling pots, no canner. You add salt, you wait, and the cabbage turns its own sugars into lactic acid, which preserves it and gives it that tangy bite.

This is a different thing from quick vinegar pickles, which get their sourness from added vinegar. Lacto-fermented sauerkraut makes its own acid from the cabbage itself. It is worth learning because it uses almost no energy, needs no special equipment beyond a jar and a weight, and the result keeps for months in the fridge.

What is actually happening

Cabbage comes covered in harmless lactic-acid bacteria. When you salt it and keep it under brine with little air, those bacteria wake up and start eating the sugars in the leaves.

Their waste product is lactic acid. As the acid builds, the brine turns sour, the environment becomes too acidic for spoilage bacteria and molds to thrive, and the cabbage is preserved.

That is the whole process. You are not adding anything mysterious. You are just giving the good bacteria already on the cabbage the conditions they need, and holding the trouble-makers at bay.

The one number that matters: 2 percent salt

Salt is the backstop that keeps the ferment safe and sour, not salty. Too little salt and bad bacteria can get a foothold before the acid builds. Too much and the good bacteria stall.

The reliable target is 2 percent salt by weight of the cabbage. Weigh your shredded cabbage, then add 2 percent of that weight in salt. For most beginners this is a better guide than a tablespoon measure, because cabbage density varies.

• For every 2 pounds (32 ounces) of cabbage, add about 0.64 ounces of salt, which is roughly 2 teaspoons. Check your salt's weight on the label if you want to be precise.
• Weighing is the honest way to do it and leaves little room for guesswork.

Use plain salt. Pickling salt or a fine salt without iodine and without anti-caking additives works well. Iodized table salt can slow the fermentation, and some additives can cloud the brine. Do not use anything labeled as a salt substitute.

What you need

Keep it simple. You likely have most of this already.

• A wide-mouth glass jar or crock.
• A clean plate, glass weight, or heavy stone to hold the cabbage under the brine.
• A way to keep the surface covered and let gases escape, like a clean cloth and rubber band, or a loose lid you burp each day.
• A heavy pan or clean bowl to bear down on the cabbage when you pack it.

You do not need a specialty fermentation kit. A crock is nice, but a plain jar with a small weight inside and a loose cover works fine.

A simple method

Here is a straightforward way to make your first batch.

1. Remove the outer leaves of a cabbage and set two or three aside to use as a cover.
2. Quarter the cabbage and remove the core.
3. Shred it thinly, about the width of a coin.
4. Weigh the shredded cabbage and measure out 2 percent of that weight in salt.
5. Sprinkle the salt over the cabbage in a large bowl and massage it with clean hands for a few minutes. The cabbage will release liquid and shrink.
6. Pack the cabbage into the jar, pressing it down firmly with a clean object so the brine rises and covers the shreds.
7. Lay a clean outer leaf over the top, then place your weight on it so everything stays under the brine.
8. Cover the jar loosely with a cloth or a loose lid and set it in a cool, dark spot, ideally around 65 to 72 F.

Leave it alone for at least a week and up to three or four. Taste it as it goes and move it to the fridge when you like the tang.

Keep it under the brine

Everything above the brine is a risk. That is the single most useful habit to learn.

• Anything floating on the surface can grow mold or a white film called kahm yeast.
• As long as the cabbage stays submerged, the ferment below the surface is safe even if the surface is ugly.
• Check each day. If the brine drops below the cabbage, add a little brine made of 2 percent salt water, about a teaspoon of salt per cup of water, or press the cabbage back down.

A few bubbles of gas escaping is normal and good. You may see little pockets of air. That is the ferment working.

What mold, film, and smells mean

Not everything that looks odd is spoiled. Learn to tell the difference.

• White or cream film on top: This is usually kahm yeast, a harmless surface yeast that can appear when a ferment sits too warm or too long. It does not ruin the food. Skim it off and keep the rest below the brine.
• Fuzzy spots in green, blue, black, or pink: This is true mold. Skim a generous layer off. If the cabbage below is still firm, under brine, and smells sour rather than rotten, the rest is commonly fine to keep, though when in doubt, throw it out.
• A sour, yeasty, or slightly earthy smell: Normal for fermenting cabbage.
• A rotten, putrid, or strongly foul smell, or slimy mush: This is a sign the ferment went wrong, usually from too little salt or too much exposure to air. Toss it and start again.

The golden rule: if it looks wrong and you are not sure, throw it out and try again. A single ruined jar is a cheap lesson.

When it is done, and why it stays in the fridge

Sauerkraut is ready when it tastes good to you, which in warm weather can be as soon as a week and in a cool cellar can take three weeks or more. Sample it with a clean spoon now and then.

Once it tastes right, move the jar to the refrigerator. The cold slows the fermentation almost to a stop. This is raw, unpasteurized cabbage, so it does not keep on a shelf like canned food. Refrigerated, a properly salted batch easily keeps for several months.

A few honest cautions

Lacto-fermented cabbage is widely regarded as a forgiving, safe ferment, but a little care keeps it reliable.

• Use clean hands, a clean jar, and clean utensils. You are encouraging one set of microbes and trying to crowd out others.
• Do not drop below about 2 percent salt. That salt level is what keeps the bad bacteria from getting a head start.
• Do not seal the jar airtight. Gases build as the ferment works, and a sealed jar can pressurize. Use a loose lid you open daily or a cloth cover.
• Fermented foods are a live, acidic, raw product. If you are new to them, start with small amounts and keep the jars refrigerated.

Keep it going

Once the rhythm clicks, sauerkraut is habit-forming. The same 2 percent salt and under-brine method works for shredded cabbage, and with small adjustments for other firm vegetables. One good fall batch can carry you through the winter, and a spare jar is exactly the kind of thing worth trading with a neighbor.

Start small, keep the cabbage submerged, keep it cool, and trust your nose. The first time you crack a jar of your own kraut, the tang is its own payoff.

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— C. Steward 🍎