KO EN ES PT FR Japanese Side dish⏱ 35 minEdit history

Koya-dofu (Freeze-Dried Tofu Simmered in Dashi)

Name: Koya-dofu (Freeze-Dried Tofu Simmered in Dashi)
Prep time: 15 min
Cook time: 20 min
Total time: 35 min
Yield: 4 servings
Cuisine: Japanese
Ingredients: 4 pieces koya-dofu; 200 g kabocha; pea shoots or snow peas; 500 ml dashi; 2 tbsp sugar; 1 tbsp mirin; 1 tbsp light soy sauce (usukuchi); 0.5 tsp salt

Tofu frozen, aged in the cold and then dried, a staple of the Japanese dried-goods shelf. Soaked, squeezed and put straight into salted dashi with kabocha, it soaks up the broth like a sponge. Most sold today has been treated to cook soft, and in plain water it falls apart.

Steps

Check the packet. If it says to soak, cover the pieces with lukewarm water and leave them until soft right through.
⏲ 5 min
Press each piece gently between your palms to squeeze out the water. Dip in fresh water and press again until the water runs clear. Do not wring.
Cut each piece into four.
Put all the simmering liquid in a pan, salt included, and bring it to the boil.
Add the koya-dofu and the kabocha, skin side down. Cover with a drop lid and simmer on low heat, never at a hard boil.
⏲ 15 min
Turn off the heat and let it cool in the liquid. Serve warm or at room temperature with some of the broth, garnished.

Variations

Ichiya-gori. Freeze a block of firm tofu for one night, thaw it and squeeze it. Not dried, so it does not keep, but the texture is close.
Shimi-dofu. In Tohoku, blocks of tofu are strung together with straw and hung under the eaves to freeze and dry.
Powdered. Broken pieces are ground to a powder and stirred into dishes in Nagano.
From silken tofu. Firm tofu becomes a sponge; silken tofu comes out more like yuba.

Tips

Salt the liquid from the start. Into salted dashi it holds together; into plain water it can fall apart.
Never boil hard. Tofu treated to cook soft splits under a rolling boil.
Press, do not wring. Wringing tears it.
Soak as the packet says. Products differ.
Seal an opened packet. The sponge picks up smells.
Past about six months it turns bitter. The fat in it oxidises.

More detail and the reasons why (2)

A sponge made by ice. Freezing and thawing explains that slow freezing grows large ice crystals that tear cell walls, and lists tofu as a case where turning spongy is sometimes exactly what you want. Koya-dofu takes that damage all the way. According to Japanese Wikipedia, the tofu is frozen, aged at a low temperature and then dried. It sits beside the pollock in hwangtaeguk, which is frozen and thawed over and over as it dries.
The softness is added at the factory. Japanese Wikipedia says traditional koya-dofu is hard, needs a night to soak and is difficult to cook soft. So most of what is sold today has been treated with sodium bicarbonate (now also potassium carbonate), which breaks down part of the protein: it soaks back quickly and is a third to a quarter as hard. The price is that in plain water it falls apart. Mapo tofu blanches its tofu in salted water to firm the surface; for koya-dofu that is not a refinement but a condition. Its neighbour on the dried-goods shelf, kiriboshi daikon, only asks for a short soak and has no such condition.