Making a Seiro Rice Steaming Box


If you’re steaming large quantities of rice for making koji, mochi, or miso there are a number of routes you can take, including making a traditional Japanese rice steaming box known as a seiro.

I used plain sawn white cedar from northern Vermont, and the satisfaction of not having to buy one of these is immense. But lets step back a moment for a little explanation.


There are tons of good ways to cook rice, but sweet glutinous rice is at its best when steamed above a pot of boiling water. In Thailand you might see a woven bamboo basket, in China perhaps a round stacking bamboo basket on top of a wok. I’ve been using a colander inside of another pot, but it doesn’t cook the quantities of rice that I need for making other fun foods, specifically for mochi tsuki. A good explanation of what the deal is with pounding mochi can be found here.


This is a book that Mark pulled off the shelf for me, and I fell in love with the mysteries of miso.


It had a good drawing of seiro, though being a woodcrafter I upgraded the joinery a bit based on other pictures I’ve seen of seiro online.


The critical dimension that you might plan making one of these around is the size of the bamboo mat that sits inside. Cedar is wonderful, lovable, excellent working wood, but you shouldn’t feel bad about making one out of pine if that’s what you have available.


I’ve been getting better with ripping the tenons bent over a low saw horse. White cedar is so soft that I use the cross-cut side of my saw for everything. Give this sawing position a try! Its not easy on the back but you gain freedom from a bench vise which you might not have access to in a lot of places you’d find yourself working. Free yourself from the “I must build a massive European joiners bench” mentality that we all start out with!


I also like holding material with my foot vertically against the end of my planing bench. This works for sawing the waste with a fret saw on dovetails too. And of course you’re feet are much faster acting clamps than a screw vice so you waste less time screwing shit. Just another little bit picked up watching shokunin on YouTube.

I borrowed some of Mark’s chisels for this work. Cedar being so soft requires exceptionally sharp chisel to pare end grain, and the steel in some of my chisels is kind of a joke. I still work with a few Harbor Freight chisels…


These are the chisels I’m talking about, Kiku Hiromaru. You can get them from Japan Tool for a mere 85,000 yen (about $750 USD at todays exchange rate). I’m not joking when I say ‘mere’, these nomi are dreamy. Literally, I dreamed about them last night.  The modern one’s are made by the son of the smith who made these, but I’d wager that the quality is still exceptional and you may even be able to find old stock to buy.


I made the hole on my steam board a bit large and added a shallow frame to help distribute the steam before the box that holds the rice.


I also let in the tenon sides of the box an eight of an inch to help restrain the wood from warping and help keep the sides steam tight. You’ll see in the line drawing from the book of miso that they can be made with a single wedge pinned through tenon, but a double tenon, though harder to cut the mortises for the wedges, resists the movement of the wood much better. Two battens mortised into the the sides hold the bamboo mat which the rice, inside of a cotton cloth, will sit upon while cooking.


And of course, with a soft wood like cedar there’s no better way to finish it off than a sharp hand plane. I’m getting some rice soaking tonight, by tomorrow I’ll be ready to pound some mochi. Maybe I’ll make some koji trays and try cultivating my own strain of mold for making sake and miso! Mark is working on a round bottomed plane for hollowing the inside of barrel staves, cedar barrels being preferred for fermenting miso.

2 thoughts on “Making a Seiro Rice Steaming Box”

  1. I can’t describe the pleasure it gives me, reading and learning about your unique interests. Definitely not run of the mill.

    Keep it coming! I’m hoping to see some barrel making soon, that link you gave in a prior post is from one of my favorite episodes.

    In the last photo, what is the thing next to your seiro, sitting next to the sharpening stones?

  2. Never knew about miso until today. Searched it out of boredom, looks cool, I guess.

    Cooperage tools always look cool, are you going to try making a sun plane for the top?

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