If using the starter culture, stir together the culture and water. Let the mixture sit while you prepare the ingredients—around 10 minutes. If using kefir whey, add it when the recipe calls for culture.
Shred the cabbage, carrots, onion, and green apple.
Assemble veggies into a large bowl and add garlic, salt and seasonings. (You may need a couple of bowls depending on how large of a batch you are making.).
Toss to combine all the ingredients.
Pack the shredded veggie mixture into a one-gallon jar or the equivalent of four quart-size containers. You can use glass or ceramic containers that can be securely sealed.
Add the starter culture or the whey and fill the jar with filtered water, leaving 2 to 3 inches of headspace, as the kraut will bubble and expand as it ferment.
Seal the container and let it sit on your kitchen counter, out of direct sunlight, for 6 days. After 6 days, place the container in the refrigerator.
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.
The veggies will be a bit fizzy and sour when ready. Place them in the refrigerator.
Storage note: This kraut can be kept in a covered airtight jar in the refrigerator for up to nine months.