Fermentation is an ancient method of preservation. It is the process responsible for many of our favorite foods & beverages including beer, bread, cheese, miso, salami, wine, and yogurt. The fermentation of vegetables is created by a process called lacto-fermentation, which enables us to preserve raw, vitamin-rich, locally-grown food during its peak season. We refer to this process as “cultured pickling” to differentiate from pickling vegetables in vinegar, another preservation technique that gained popularity with the rise of commercially distributed foods. Comparatively, cultured foods retain live bacteria, yeasts, and enzymes, like this classic sauerkraut.
Peel off the two of the cabbage leaves and save them (you'll use them later). Cut out the core and finely chop it, and chop or shred the rest of the cabbage. Mix all of the cut cabbage with the sea salt in a large bowl. Squeeze the cabbage and salt together with your hands, kneading it thoroughly until it releases its juice. Let it sit out for an hour to draw out more liquid.
Pack the kraut tightly into your clean gallon vessel using your fist or a wooden tamper to ensure that there is some liquid above the kraut. Lay the two reserved whole cabbage leaves on top of the packed kraut and submerge them in the liquid. If there is not enough liquid to cover, add just enough water to submerge. Be sure to leave about an inch of headspace from the top of the vessel as carbon dioxide, which is naturally produced, will cause everything to expand. Use a ceramic weight or other creative weight if necessary to keep the vegetables submerged.
Cover loosely with a lid or airlock lid and secure tightly on the jar. Let the cabbage ferment in a dark place (out of direct sunlight) for a minimum of 5 days and up to 30 days for a more complex and sour ferment.
The large cabbage leaves on top are there to provide an extra layer of protection against surface mold. Taste the kraut below every couple of days for your desired flavor. Discard the outer leaves if mold appears. Don't stress about mold! Transfer into the refrigerator to store for 6 to 12 months.