Zouni is a soup which basically contains mochi rice cake, and is eaten on new year’s day. Different ingredients are used depending on each region. The most common ingredients used for zouni are mochi, tofu, chicken, vegetables such as potatoes, spinach, and carrot.
It is not sure where original zouni comes from, but there are few theories. In the samurai society, there was a dish similar to zouni, which was called houzou. Houzou used ingredients such as mochi, vegetables, and dried products. Eating mochi on new year’s day was a custom from older days, and eating houzou was ritualized in samurai society, which later spread among the common people.
However, before the modern days, there was a custom in upland cropping areas prohibiting to eat mochi for the first three days of new year’s. The upland cropping area did not produce rice, and products made from rice were considered foreign, which was not proper to offer to deity to wish fertility. So in those areas, zouni without mochi was made, and in some regions in Japan still make such zouni.
The big difference of zouni in Kanto region, eastern part of Japan, and Kansai region, western part of Japan, is that zouni in Kanto region use round baked mochi with thin taste soup, and zouni in Kansai region boils square shaped mochi, and use miso based soup. In many regions, local products are used for zouni. For example, in the Tohoku and Hokuriku region, northern part of Japan, seafood are often used.
In Nara prefecture, where Todaiji temple is famous, some households use only white ingredients such as Japanese yam, Japanese radish, and tofu. On the other hand, some households add carrot, and cook red and white zouni, because red and white colors are considered auspicious.