There are many variations of ozoni, which strongly reflect regional food culture.
Broadly speaking, ozoni in the Kansai region, where the court noble culture remains, tend to use round mochi, while in the Kanto region, where the samurai culture of the Edo period remains, tend to use rectangle mochi.
Round mochi, in which the spirit of Toshigamisama resides, is the original form of mochi, but in cold regions, if you roll the mochi by hand, air bubbles form inside the mochi and it easily breaks.
Therefore, in the Kanto region, noshimochi, which is made by applying pressure to push out air bubbles, is used. When noshimochi is cut into pieces, it naturally forms a rectangle shape, which is why rectangle mochi is more common in the Kanto region.
Also, when you put the rectangle mochi in ozoni, it is most likely to be baked before adding it to the soup. When mochi is baked, it expands and the corners are removed. The shape then becomes closer to round, which is the original meaning.
It is thought that this kind of wisdom spread along with Sankin Kotai system (In essence, the system demanded simply that daimyo reside in the Tokugawa castle at Edo for periods of time, alternating with residence at the daimyo's own castle.), but ozoni was rearranged from place to place and became diverse throughout the country.
In addition to regional characteristics, ozoni is filled with family history. The family's ozoni is formed by mixing the ozoni of the father's and mother's sides and reflecting their preferences, so even between neighbors, ozoni styles are probably different. It is interesting to find out the origins of your family's ozoni, if you or your family makes any. Even if your food culture has nothing to do with Japanese, it can also apply to any dishes, either Japanese or non-Japanese. Please cherish the taste with your family.
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