Final answer:
Opened sauerkraut can last for several months in the refrigerator due to the preservative effects of its acidic environment created by lactic acid bacteria.
Step-by-step explanation:
Once opened, sauerkraut can typically be kept in the refrigerator for up to several months, provided it is stored properly. The lactic acid bacteria found in sauerkraut thrive at a pH close to 4.0, creating an acidic environment that helps to preserve the food. This level of acidity is responsible for giving sauerkraut its tangy flavor, while also making it less hospitable to the microbes that cause food spoilage, as most of them prefer a near-neutral pH and do not tolerate acidity well.