Make a 2% brine: dissolve the salt in hot water; set aside to cool.
Remove blemished or dirty outer leaves from cabbage; discard or compost. Rinse the cabbage head in non-chlorinated water. Cut cabbage in half, then cut the dense core from the middle (some people eat the core raw or cook with it; otherwise, compost it). Cut the remaining cabbage head in one-inch strips, lengthwise, to easily fit in your food processor with the “S” blade attachment. Process the cabbage as minimally as possilbe in two to three batches until it is finely ground yet not liquified. It should look mealy. For each batch, stop the food processor a couple of times to scrape down larger chunks of cabbage from the sides of the bowl to ensure even processing. Combine each batch of mealed cabbage into a large bowl.
The combined weight of cabbage and any additional vegetables (e.g. onions, garlic, etc.) should total three pounds (1362 grams). Reduce the amount of cabbage if you plan to add onions for a cabbage-onion kraut juice or any other vegetables. Ensure all vegetables are ground to a fine pulp in a food processor, although do not liquify.
Add any whole spice to the bowl of cabbage pulp. Mix to distribute. Pack the cabbage in a 3 L airlock jar. Use a stainless steel canning funnel for funnelling the pulp into the jar without a mess. Packed cabbage pulp should fill the jars about halfway. Slowly pour the cooled brine overtop, until it reaches the shoulder. Do not continue to add extra brine past the shoulder.
Clean around the mouth of the jar with paper towel. Fasten the rubber gasket around the underside of the lid. Fill the 3-piece airlock with water to the fill line; insert the airlock and clamp lid shut.
Store at room temperature, between 18-21ºC, out of direct sunlight for 4-7 days or until bubbles cease to surface. Transfer to cold storage (a fridge or cold room below 12ºC) with the airlock in place. Leave for 10-12 weeks - less time if stored in a cold room, more time in a fridge.
Once fermentation is complete, pour the pulpy juice mixture in 1- to 2-cup batches through a nut-milk bag or alternative fine-knit mesh (old sheer curtains work well). Squeeze until pulp is dry and fibre remains. Compost the pulp. Transfer juice to a swing-top bottle to continue restricting oxygen; discard the fibre. Refrigerate and use within three months. Start with 1 ounce taken with meals and progress to ¼ cup at one sitting, as tolerated.