From the wiki: “Mochi is Japanese rice cake made of mochigome, a short-grain japonica glutinous rice. The rice is pounded into paste and molded into the desired shape. In Japan it is traditionally made in a ceremony called mochitsuki. While also eaten year-round, mochi is a traditional food for the Japanese New Year and is commonly sold and eaten during that time.
“The first recorded accounts of mochi being used as a part of the New Year’s festivities was from the Japanese Heian period (794-1185). The nobles of the Imperial Court believed that long strands of freshly made mochi symbolized a long life and good well-being, while dried mochi acted to make one’s teeth tough and more durable. Accounts of mochi have also been read in the oldest Japanese novel, ‘The Tale of Genji’.
“Mochi continues to be one of the traditional foods eaten around Japanese New Year, as it is sold and consumed in abundance around this time. A special type of mochi, called kagami mochi (mirror mochi) is placed on family altars on December 28 each year. Kagami mochi is composed of two spheres of mochi stacked on top of one another, topped with an orange (daidai). On this occasion, which was originally practiced by samurai, the round rice cakes of kagami mochi would be broken and thus, symbolizing the mirror’s opening and the ending of the New Year’s celebrations.”