This recipe uses Umeboshi plum vinegar. It is made from the brine used for Japanese pickled plums, which has wonderful sour and salty characteristics. The vinegar is considered to be alkalizing and is helpful for detoxing. Plain rice can be used and is a suitable substitute, but if you're feeling adventurous, the bamboo variety will be a tasty alternative. As an option, you can serve with seaweed salad.