Mochitsuki is a Japanese cooking technique.
It is the act of pounding steamed sticky rice, in order to make “mochi” rice cakes.
The steamed rice must be pounded when it has cooled down a bit, but is still hot. It is put into a mortar called an “usu” and pounded with a mallet on a handle called a “kine.” The mortar is actually the size of a small barrel, a few feet tall, usually made of wood, but can also be made of stone. The mallet is quite big — the handle is several feet long, and the hammer part about a foot, foot and a half long, flat at its business end, and very heavy.
You swing the mallet by bringing it up over your shoulder and aim to get the actual hammer business end of it landing inside the barrel. You mustn’t hit the side of the mortar, or you may cause wood chips from the wooden usu to splinter off into the rice, or in the case of a stone usu, cause the mallet itself to chip or splinter.
In addition to the pounder, another person is needed to be turning the rice over. People take turns to relieve each other. Usually the men do the pounding, the women doing the turning, occasionally adding a bit of water if it gets too dry. The rice needs to be pounded until it is a smooth, consistent paste, sometimes referred to in English as a “dough.”
The Japanese have, of course, long since invented electric machines that do it for you (the machines are multi-function, and will also do bread and pizza dough, make custards, cook noodles, etc), though most people just buy their mochi already made now. Purists swear the machine-made mochi never tastes as good.
Doing it the traditional way is now mostly done as a traditional activity at holidays, particularly at New Year. The mortar is very large, and requires storage space that usually city dwellers don’t have. Many community groups schedule a Mochitsuki event 3 days before New Year
Leftover mochi dough should be put in your compost bin or garbage, not down the drain as it will clog your drain quite easily. Every New Year, reminders are issued in newspapers about not letting it go down your drains.
Japanese folk tales tell of Mochitsuki being done on the moon by rabbits (with bunny-size mortars and mallets, of course.)
It’s a big moment in a boy’s life when he is allowed to first wield the mallet.