Squeeze and massage the cabbage for about 15 minutes. Place into the mason jar, packing it down every so often with your fist to remove air bubbles. Pour any cabbage liquid into the jar.
Place the outer leaf flat on top of the sliced cabbage. Push a small jar inside the mason jar on top of the cabbage to weight it down. Cover with a cheesecloth. This will ensure that the cabbage can breathe.
Store at room temperature in the dark. As it ferments, check to see that the cabbage stays under the liquid. Start tasting after 7 days. When it’s tangy enough to your liking, store in the refrigerator.