Three days into the fermentation process, taste your sauerkraut. It should be lightly sour, fragrant and maybe even a little effervescent. With each passing day, the kraut will get more sour and pungent; it will also continue to soften as the fermentation breaks down cell walls. If you prefer your kraut crisp and mild, it should be ready within three to five days; if you prefer it softer and funkier, a week or longer may be required. When the sauerkraut is to your liking, seal the jar and store in the refrigerator for up to several weeks. The kraut will continue to ferment in the refrigerator, though much more slowly.