Prep and Pack
1. Chop or grate cabbage, finely or coarsely, with or without hearts, however you like it. Sprinkle salt on the cabbage as you go. The salt pulls water out of the cabbage (through osmosis), and this creates the brine in which the cabbage can ferment and sour without rotting.
2. Pack cabbage into crock a bit at a time and press it down hard to help force water out of the cabbage.
3. Cover kraut with a plate or jar that fits snugly inside the crock. Place the clean weight on it, which will force water out of the cabbage and then keep the cabbage submerged under the brine. Cover the whole thing with a cloth to keep dust and bugs out.
4. Press down on the weight to add pressure to the cabbage and help force water out of it every few hours until the brine rises above the cover. This can take up to about 24 hours. Some cabbage, particularly if it is old, contains less water. If the brine does not rise above the plate level by the next day, add enough salt water to bring the brine level above the plate. Add about a teaspoon of salt to a cup of water and stir until it's completely dissolved.
Wait and ferment
5. Leave the crock to ferment in a corner of the kitchen, or somewhere out of the way. Check the kraut every day or two. The volume reduces as the fermentation proceeds.
6. Taste the kraut after a few days. It should start to get tangy. The taste gets stronger as time passes, generally over 2-3 weeks, though warm environments will speed the fermentation process. Once it gets to your desired flavor, remove the weight and plate and add a lid. Store it in the fridge for up to a few months. (See below.)
Notes: Sometimes mold appears on the surface. Skim what you can off of the surface although you will probably not be able to remove all of it. Don't worry too much, just get what you can and clean the plate and weight each time you remove them. The kraut itself is under the anaerobic protection of the brine. Avoid mold/rot by sanitizing all of your equipment, keeping your kraut submerged in the brine, and keeping it salty!
According to the National Center for Home Food Preservation, it should safely keep for a few months.