Remove the outer leaves of the cabbage and discard. Cut the cabbage into quarters, remove the core, and shred the cabbage into thin strips.
In a large bowl, combine the shredded cabbage and salt. Toss to coat the cabbage evenly with salt. Let it sit for about 10 minutes to start drawing out moisture.
After 10 minutes, use clean hands to massage and squeeze the cabbage. This helps release more juice from the cabbage, which is crucial for fermentation.
If using, mix in the caraway seeds, juniper berries, grated apple, and finely chopped onion.
Pack the cabbage mixture into a clean, sterilized fermentation crock or jar. Press down firmly to remove air bubbles and ensure the cabbage is submerged under its own juice. Leave about 1-2 inches of headspace at the top of the jar.
If using a crock, cover it with a clean cloth or lid. If using a jar, cover with a lid or plastic wrap. To keep the cabbage submerged, place a weight (like a small plate or fermentation weight) on top of the cabbage. This prevents mold from forming.
Leave the cabbage to ferment at room temperature (around 65-75°F or 18-24°C) for 1 to 4 weeks. Check the sauerkraut daily to ensure it remains submerged and to taste it periodically. The sauerkraut is ready when it reaches your desired tanginess.
Once fermented to your liking, transfer the sauerkraut to the refrigerator. It will keep for several months in the fridge.
Enjoy your meal!