Shred or chop, cabbage, and place in a large bowl.
Add salt and toss to combine.
Pack cabbage into your jar. Add kefir whey and fill with water, leaving two inches of headspace at the top for your kraut to expand and ferment.
Place a secure lid on the jar (airlock jarlids are optional) and set in a cool place, out of sunlight for 6 to 7 days. Taste veggies after 6-7 days and if they taste tart like kraut they're done. Place jar in the refrigerator, where they will stay for many months perfectly preserved.
Check the vegetables every day to make sure they are fully submerged in the water. If they have risen above the water, simply push them down so they are fully covered by the water. If any white spots formed because the veggies rose above the water, do not worry. Remember, this isn’t harmful. Just scoop out the vegetables that have the white spots on them and push the rest back under the water.