In short: keep it until kagami biraki (often January 11)
Display the kagami mochi until kagami biraki: January 11 in most areas, and January 15 or 20 in Kansai, with regional variation. Note this is a different date from when the kadomatsu and shimenawa come down (the new-year period, January 7 and so on).
Kagami mochi is treated differently from other decorations. Where the kadomatsu and shimenawa are "markers to welcome the deity," the kagami mochi is the very seat (yorishiro) in which the year deity dwells. So even after the new-year period ends, you keep it until you eat it, deity and all, on kagami biraki.
Kagami biraki dates vary by region
| Region | Kagami biraki |
|---|---|
| Most areas, incl. Kanto | January 11 |
| Parts of Kansai | January 15 (Koshogatsu) or 20 |
| Parts of Kyoto and nearby | January 4 in some places |
Originally kagami biraki was on January 20 nationwide, but in the Edo period many areas moved it to the 11th to avoid the 20th (a shogun's memorial day). Where the new-year period runs to the 15th, as in Kansai, doing kagami biraki during that period would clash, so some areas kept it on or after the 15th.
Dates vary by region and household. Follow your local custom.
Why "opening," and no blade
Eating the kagami mochi is called "kagami biraki," and the words "cut" and "break" are avoided:
- "Cut" evokes seppuku: in samurai society, turning a blade on the kagami mochi was seen as ill-omened
- "Opening" is auspicious: "break" is avoided too; "open" suggests fortune and happiness opening up
- No blade: the proper way is to break it with a wooden mallet or by hand - also so no blade touches the mochi the deity dwells in
Hardened kagami mochi becomes easier to break if soaked in water for half a day and then softened in the microwave. Modern vacuum-packed kagami mochi (with individually wrapped cut mochi inside) skips this step entirely.
How to eat the mochi at kagami biraki
Eating the kagami biraki mochi means receiving a share of the year deity's power and wishing for a year of good health. Recommended ways:
- Oshiruko / zenzai: the kagami biraki classic; the red of the beans also wards off evil
- Fried mochi (kakimochi): break small, dry, deep-fry and salt - ideal for rescuing hardened mochi
- Added to ozoni: for enjoying ozoni even after the new-year period (Ozoni: Regional Styles & Recipes)
- Grilled mochi: grilled with soy sauce and nori, kinako, or sweet bean paste
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Frequently asked questions
How long is kagami mochi displayed?
Until kagami biraki: January 11 in most areas, 15 or 20 in parts of Kansai. This is separate from the new-year period (January 7 and so on).
Why call it "kagami biraki," and not say "cut"?
Because "cut" evokes seppuku and is ill-omened, it is rephrased as the auspicious "open." No blade is used; a wooden mallet or hands break it.
How do I break hardened kagami mochi?
Soak it in water for about half a day, then microwave to soften and it will pull apart by hand. To use a mallet, let it dry until it cracks.
What does displaying kagami mochi mean?
It is the seat where the year deity dwells. The stacked round mochi expresses "growing older in harmony," and eating it at kagami biraki shares the deity's power for good health.
Can I eat mouldy kagami mochi?
Some say scraping the surface is fine, but mould filaments reach inside, so it is safer not to force it. Vacuum-packed kagami mochi is hygienic and easy to handle.