Traditionally, the kayu ura ritual took place on the 15th day of the first lunar month, but since the adoption of the Gregorian calendar it has been conventional to perform the ceremony on January 15th; this date is known as ko-shōgatsu or "Little New Year". Divination by gruel is generally used for agricultural predictions; it is presumed to predict the weather and harvests for the coming year.
The ceremony takes various forms. A common practice is to stir a large pot of rice gruel (粥 (kayu)) with a split wooden stick, and to observe the number and organisation of the grains that adhere to the stick when it is removed. In another variation, known as tsutsugayu shinji, multiple hollow cylinders made of split bamboo or reeds are placed in the gruel, each cylinder corresponding to a specific month. Shinto prayers are chanted and the rice porridge is then left overnight. The following morning, the cylinders are cut open and the contents examined – the more rice that has stuck to the inside of the tube, the more propitious the harvest. If multiple tubes are used, these usually correspond to specific months of the year, and the results are recorded on a month-by-month basis. The tsutsugayu shinji variation is practiced at the Suwa Grand Shrine.
A further variation on the ritual is used in Akita, in which the gruel is not stirred but is instead smeared on a wooden pole; predictions are made based on how much rice sticks to the pole and the patterns that it makes. The oldest form of this ceremony, and the precursor to those listed above, involves a Shinto priest examining the mould that has formed on a bowl of rice porridge that has been stored in a special box for several days.
- Robertson, Stephen (2016). "Hope that sustains: revisiting New Year's divination at Suwa Taisha" (PDF). Contemporary Japan. 1 (28): 101–122. doi:10.1515/cj-2016-0006. Retrieved 14 February 2017.
- Kentarō, Suzuki. "Kayu'ura". Encyclopedia of Shinto. Kokugakuin University. Retrieved 14 February 2017.
- Brian Bocking (30 September 2005). A Popular Dictionary of Shinto. Routledge. p. 12. ISBN 978-1-135-79739-3.
- Satow, (16 July 2014). Ancient Japanese Rituals. Taylor & Francis. p. 46. ISBN 978-1-317-79291-8.
- "The Ritual of Kayu-ura Kayubiraki". Imori Shrine. Retrieved 14 February 2017.