What Do I Need to Make Sauerkraut? At the most basic, all you need is cabbage, salt, and some sort of container to store it while it's fermenting. It's important that the cabbage remain submerged in its liquid during fermentation. When making sauerkraut in a crock, you usually place a weighted plate over the cabbage to pack it down and keep it submerged. When fermenting in a mason jar, inserting a smaller jelly jar filled with rocks or marbles in the mouth of the larger jar serves the same purpose. The cabbage near the surface tends to float, so when fermenting in a mason jar, you need to either tamp down the cabbage a few times a day or place a large outer leaf of cabbage over the surface of the shredded cabbage to hold it down. Also be sure to keep the jar covered at all times with a clean cloth or piece of cheese cloth. This will allow airflow, but prevent dust or insects from getting into the sauerkraut.
How Long Does It Take To Make Sauerkraut? For a small quart-sized batch like we're making today, the minimum time is about three days, though the kraut will continue to ferment and become tastier for many days after that. As simple as it sounds, the best rule of thumb is to keep tasting the kraut and refrigerate (or take it cellar temperature) when it tastes good to you. The sauerkraut is safe to eat at every stage of the process, so there is no real minimum or maximum fermentation time.
What Can Go Wrong? Not much! You may see bubbles, foam, or white scum on the surface of the sauerkraut, but these are all signs of normal, healthy fermentation. The white scum can be skimmed off as you see it or before refrigerating the sauerkraut. If you get a very active fermentation or if your mason jar is very full, the brine can sometimes bubble up over the top of the jar. This is part of the reason why I recommend using a larger mason jar than is really necessary to hold the cabbage. If you do get a bubble-up, it's nothing to worry about. Just place a plate below the jar to catch the drips and make sure the cabbage continues to be covered by the brine. It is possible that you might find mold growing on the surface of the sauerkraut, but don't panic! Mold typically forms only when the cabbage isn't fully submerged or if it's too hot in your kitchen. The sauerkraut is still fine (it's still preserved by the lactic acid) — you can scoop off the mold and proceed with fermentation. This said, it's still important to use your best judgement when fermenting. If something smells or tastes moldy or unappetizing, trust your senses and toss the batch.
Canning Sauerkraut: You can process sauerkraut for longer storage outside of refrigeration, but the canning process will kill the good bacterias produced by the fermentation process. See this tutorial from the National Center for Home Food Preservation for canning instructions.
Larger or Smaller Batches: To make larger or smaller batches of sauerkraut, keep same ratio of cabbage to salt and adjust the size of the container. Smaller batches will ferment more quickly and larger batches will take longer.
Hot and Cold Temperatures: Do everything you can to store sauerkraut at a cool room temperature. At high temperatures, the sauerkraut can sometimes become unappetizingly mushy or go bad. Low temperatures (above freezing) are fine, but fermentation will proceed more slowly.