To make brine, dissolve 1 tsp (5 ml) salt in 1 cup (240 ml) water and set aside.
Remove any bruised outer leaves of cabbage. Cut cabbage into quarters then remove and discard the core sections. Slice cabbage very thinly and place in a large bowl, then sprinkle with 1 Tbsp (15 ml) salt. Massage salt into cabbage, squeezing to release liquid. Cover bowl and let stand at least 1 hr.
Toss cabbage a few more times, squeezing to release any extra liquid. Then pack cabbage into the jar, tamping down firmly with a spoon. Leave at least 2 in. (5 cm) of headspace. Pour any liquid collected in the bowl over the cabbage, pressing down firmly to help liquid cover cabbage. There may not be a lot of natural brine at this time, but the cabbage will continue to release it slowly.
Place spring on top of cabbage, then twist lid on.
Wipe jar down and cover with a cloth. Store in a cool (68°F-72°F /20°C-22°C) place for 24-36 hours. If after this time the brine does not cover the cabbage by 1 in. (2.5 cm), remove lid and spring, and add some additional brine to cover. Wipe jar rim before replacing spring and lid. Discard any extra brine.
Check daily to make sure vegetables remain submerged in brine. The cabbage will become translucent and slightly yellow in color as it ferments.
Let the sauerkraut ferment for 2 weeks, then taste for the mild tangy flavor. If the flavor is to your liking, proceed to step 8. If you prefer a stronger flavor, ferment an additional 1-3 weeks until flavor develops.
Once desired flavor is reached remove spring and add additional fresh brine as necessary to cover. Wipe jar rim before replacing lid or use a Ball® canning lid. Store in refrigerator up to 6 months.