Chop the cabbage into 1/2 inch wide pieces. Place it in a bowl with the salt and fish sauce and begin crushing it with your hands. Continue crushing it until the cabbage starts releasing water, and keep crushing it for another 15 minutes after that. Add the red pepper flakes, garlic, and ginger and mix well.

Empty the mixture into the fermentation crock and compress it into the bottom of the container. Place the weights in the crock and over the mixture. If there isn't an inch of brine above the weights, add water and a teaspoon or two of salt until the weights are covered by 1 inch of water.

Place the lid on the crock and fill the lip around the lid with water to create an air-tight seal. Refill the lip as necessary over the coming weeks to ensure the water lock stays in place and keeps out any bugs or bacteria. Allow to ferment for 2 weeks and up to 2 months.

Once the desired fermentation is reached, remove the sauerkraut from the crock and store it submerged in brine in clean mason jars fitted with lids in the refrigerator. They will keep in the refrigerator like this for 1 year. Makes about 2.5 liters of sauerkraut.