Remove the outer leaves of the cabbage and throw them away. Remove the next set of leaves and set them aside.Cut the cabbage into quarters and remove the core.Thinly slice the cabbage using a sharp knife or mandoline slicer.
Place the sliced cabbage in a large mixing bowl.Sprinkle the sea salt over the cabbage.Massage the salt into the cabbage for about 5-10 minutes until it becomes soft and releases its juices.
Pack the salted cabbage tightly into a large glass jar or fermentation crock.Press down firmly to remove any air pockets and ensure the cabbage is submerged in its juices.Use the reserved outer leaves to cover the top of the sliced cabbage.
Place a weight on top of the cabbage to keep it submerged. This could be a clean glass jar filled with water or a fermentation weight.Cover the jar with a clean cloth or lid with airflow to allow gases to escape during fermentation.
Store the jar at room temperature, out of direct sunlight, for 1-4 weeks. The fermentation time depends on your taste preference; the longer it ferments, the tangier it will become. Check the sauerkraut daily to ensure it remains submerged in its liquid to prevent molding.
Begin tasting the sauerkraut after one week. Once it reaches your desired flavor, transfer it to the refrigerator to slow down the fermentation process. Homemade sauerkraut can be stored in the fridge for several months.