せいろのカビ

Mould on a bamboo steamer: what the makers say to do

English cleaning guides treat mould on a bamboo steamer as something you scrub off. A Japanese seiro maker treats a blackened patch as a reason to stop using the basket. The two Japanese sources here do not agree with each other either, and where they differ this page gives both.

What the two Japanese sources say to do

Kagoya, a Tokyo bamboo-goods shop that has sold seiro since the early 1970s, gives three steps in order: wash the mould off, pour boiling water over the steamer to disinfect it, and if it still will not come off, dry the steamer and take the mould off with sandpaper. If you are still uneasy about the spot afterwards, it says to put a plate or a sheet of cooking paper between the food and the bamboo. Takemi, a bamboo seiro maker in Saitama, gives no removal route at all: it says a blackened area may be mould and that in that case it recommends replacing the steamer, and it puts the working life of a bamboo seiro at roughly one to two years, treating it as a consumable. For prevention it suggests spraying the basket with disinfectant alcohol.

Where the English routine parts company

The routines part company at an ordinary step. The Fork Bite, an English guide to these steamers, starts a new one by washing it in hot soapy water and then immersing it in a bowl of hot water for about thirty minutes, and its mould section says the steamer will soon be as good as new. Takemi rules out both halves of that: it calls soaking strictly forbidden and names the damage as splitting and the inner frame coming loose, and it asks for water or lukewarm water rather than detergent, because the detergent soaks into the wood. This is not a divide between languages. A second English guide, Bamboo Wood, tells readers to avoid soaking and to avoid soap for the same reasons. What is missing from both English pages is the other answer — that the basket may be past saving. Neither raises it, and one says the opposite outright.

Before the first use

Takemi asks for one step before the first use, which it calls karamushi — steaming the basket empty. Wet the whole steamer and shake off the surplus; bring a pan to the boil and, once steam is rising, set the empty seiro on it and steam for about ten minutes over a medium flame; then rinse off what has been drawn out and dry it thoroughly. It gives the reason as durability: the basket is less likely to split or warp afterwards. Kagoya describes the same empty steaming for a different purpose — to drive out the smell of new wood, and the bamboo’s astringency, faster.

Where the two disagree

The two Japanese sources also disagree with each other, and this page gives both rather than the tidier one. On detergent: Takemi says to use water or lukewarm water and not detergent, because the components soak into the wood; Kagoya says that when the basket is greasy a neutral detergent is fine provided it is rinsed off thoroughly. On how long a seiro lasts: Takemi gives roughly one to two years and calls it a consumable; Kagoya says that at ordinary household use it should last a long time. It is worth noticing which way the commercial interest runs. The source that says replace it makes and sells seiro. The source that gives you a way to keep using the one you have sells them too.

What follows from it

• ✗Do not soak it. Takemi calls soaking strictly forbidden and gives the damage as splitting and the inner frame coming loose — and soaking is the step both the usual English mould routine and the usual English new-steamer routine are built on.
• ✗No dishwasher, no tawashi, no abrasive powder. Takemi rules out all three for ordinary washing, on the grounds that the bamboo fibres splinter. Kagoya’s sandpaper is a last resort on a dried basket, not a way to wash one.
• ✓Keep the food off the bamboo. Cooking paper, a plate, or leaf vegetables under whatever you are steaming. Both sources suggest it, and Takemi names food residue left on the basket as a cause of mould in its own right.
• ✓Dry it before it is put away, and store it with air around it. Kagoya asks for a well-ventilated place such as an upper shelf, thoroughly dried, and not wrapped in a plastic bag. The Fork Bite gives the same warning about plastic containers, so this one is not in dispute.

Two things that are not mould

Two things that look like trouble and are not. Kagoya says brown water in the pan under a new steamer is the bamboo’s own shibu — its astringency — leaching out, that a pale steamed bun can pick up a faint tint from the same thing, that it is harmless if eaten, and that both fade with use. It says the same of the smell of new wood, and that steaming the basket empty clears the smell and the shibu faster. On materials, Kagoya stocks bamboo, sugi cedar and hinoki cypress and says the method and the steaming times are the same for all three, so that choice is about appearance and scent rather than performance. Takemi’s care page is written for bamboo specifically.

Where to look

There is no shop link on this page. One of the two Japanese sources answers a blackened basket with “replace it”, and a link to a new steamer under that sentence would make this page an advertisement for the more expensive of the two answers. If yours does turn out to be finished, the figure worth carrying into the next purchase is the maker’s own — one to two years of use for a bamboo seiro — weighed against the shop that says one lasts a long time. Both are linked below.