Sauerkraut has been found to last anywhere from a few weeks to months, depending on whether it's pasteurized or not. Pasteurized sauerkraut has been suggested to last longer, but this means that once it's opened, you should eat it within 3 to 4 weeks. Unpasteurized sauerkraut retains more of the good bacteria that get killed in the heat treatment process. This kind of sauerkraut will stay fresh for 4 to 6 months when refrigerated in between uses. You should watch out for different bacterial strains getting into your jar as they will disrupt the natural bacteria caused by fermentation and will cause your sauerkraut to spoil. Using clean utensils every time you eat it will help you avoid this.