1 medium head green cabbage (about 3 lb.)
1 1/2 Tbsp. kosher salt
1 Tbsp. caraway seeds (optional, for flavor)
Slice the cabbage. Discard the wilted, limp outer leaves. Cut the cabbage into quarters and trim out the core. Slice each quarter down its length, making 8 wedges. Slice each wedge crosswise into very thin ribbons. Combine the cabbage and salt.Transfer the cabbage to a big mixing bowl and sprinkle the salt over top. Begin working the salt into the cabbage by massaging and squeezing the cabbage with your hands. At first, it may not seem like enough salt, but gradually, the cabbage will become watery and limp — more like coleslaw than raw cabbage. This will take 5-10 minutes. If you'd like to flavor your sauerkraut with caraway seeds, mix them in now.
Grab handfuls of the cabbage and pack them into the canning jar. If you have a canning funnel, this will make the job easier. Every so often, tamp down the cabbage in the jar with your fist. Pour any liquid released by the cabbage while you were massaging it into the jar. Place one of the larger outer leaves of the cabbage over the surface of the sliced cabbage. This will help keep the cabbage submerged in its liquid.
Once all the cabbage is packed into the mason jar, slip the smaller jelly jar into the mouth of the jar and weigh it down with clean stones or marbles. This will help keep the cabbage weighed down, and eventually, submerged beneath its liquid. Cover the mouth of the mason jar with a cloth and secure it with a rubber band or twine.
Over the next 24 hours, press down on the cabbage every so often with the jelly jar. As the cabbage releases its liquid, it will become more limp and compact and the liquid will rise over the top of the cabbage. If after 24 hours, the liquid has not risen above the cabbage, dissolve 1 tsp. of salt in 1 cup of water and add enough to submerge the cabbage.
Ferment the cabbage for 3-10 days. As it's fermenting, keep the sauerkraut away from direct sunlight and at a cool room temperature — ideally 65°F to 75°F. Check it daily and press it down if the cabbage is floating above the liquid.
Because this is a small batch of sauerkraut, it will ferment more quickly than larger batches. Start tasting it after 3 days — when the sauerkraut tastes good to you, remove the weight, screw on the cap and refrigerate. You can also allow the sauerkraut to continue fermenting for 10 days or even longer. There's no hard and fast rule for when the sauerkraut is "done" — go by how it tastes.
While it's fermenting, you may see bubbles coming through the cabbage, foam on the top, or white scum. These are all signs of a healthy, happy fermentation process. The scum can be skimmed off the top either during fermentation or before refrigerating. If you see any mold, skim it off immediately and make sure your cabbage is fully submerged; don't eat moldy parts close to the surface, but the rest of the sauerkraut is fine.
This sauerkraut is a fermented product so it will keep for at least 2 months and often longer if kept refrigerated. As long as it still tastes and smells good to eat, it will be. If you like, you can transfer the sauerkraut to a smaller container for longer storage.