The primary ingredient in traditional Japanese miso soup is miso paste, a fermented soybean product. Miso is made by fermenting soybeans with salt and a specific type of mold called koji. This paste is rich in umami flavor and is the foundation of miso soup, which may also include ingredients like tofu, seaweed, and green onions. Miso soup is a staple in Japanese cuisine, often enjoyed as a breakfast dish or side. It is celebrated not only for its delicious taste but also for its nutritional benefits, including probiotics and essential vitamins.