Tokoroten (Seaweed Jelly Noodles in Vinegar Soy)

Name: Tokoroten (Seaweed Jelly Noodles in Vinegar Soy)
Prep time: 25 min
Cook time: 1 h 10 min
Total time: 1 h 35 min
Yield: 4 servings
Cuisine: Japanese
Ingredients: 30 g dried tengusa seaweed; 1.5 L water; 1 tbsp rice vinegar; 3 tbsp soy sauce; 3 tbsp rice vinegar; 1 tsp sugar; 2 tbsp dashi; 1 tsp karashi mustard; 2 spring onion; 1 tsp toasted white sesame; 0.5 sheet nori

A Japanese summer snack: a red seaweed simmered for an hour and the water left to set. This site already has several setting agents — gelatine in panna cotta, collagen in pyeonyuk, starch in dotori-muk, agar in yokan — and it has never made any of them. Tokoroten does not add agar; it extracts it. There is no powder anywhere in the recipe, because the gelling agent is what leaches out of the seaweed cell walls into hot water. And freezing this dish over Edo winter nights, again and again, is how powdered kanten was discovered — an ingredient invented by exactly the mechanism that makes hwangtae.

Steps

Put the dried tengusa in a big bowl and rub it under at least four changes of water. It is seaweed, so sand and shell fragments come with it, and anything you leave ends up on the floor of the jelly. Then soak it in cold water for 30 minutes.
⏲ 30 min
Put the seaweed in a pot with the 1.5L of water and 1 tbsp of vinegar, bring it to the boil and drop to a bare simmer. The vinegar is not for flavour: acid loosens the cell walls so the agarose can leave them for the water.
⏲ 10 min
Simmer 50-60 minutes with the lid ajar. The seaweed shrinks to less than half its volume and the liquid turns visibly slippery. When a thin film of it clings to the back of a spoon instead of running off, it is extracted.
⏲ 60 min
Strain it through cloth while it is still very hot. Agar begins to set around 40°C, so a cooling liquid clogs the cloth. Press the last of it through with the back of a ladle.
⏲ 5 min
Pour it into a shallow square tray, 2-3cm deep, and leave it at room temperature. It sets in an hour. Not needing the fridge is the difference from gelatine, and it is the one yokan explains: agar sets at around 40°C.
⏲ 60 min
Mix the nihaizu and chill it. Put the karashi in a small dish of its own.
⏲ 5 min
Turn the set jelly out and cut it into 5mm square-section strands. In Japan it is pushed through a wire grid in a box called a tentsuki, but a knife does the job — what matters is the square section, because it gives the dressing plenty of surface to cling to.
⏲ 10 min
Serve it cold and pour the nihaizu over at the last moment. Spring onion, sesame and nori on top, karashi on the side. Dressed ahead, the sauce simply pools underneath and the jelly still tastes of nothing.
⏲ 2 min

Tips & Variations

Variations

Making it from powdered kanten is not the same dish. Dissolving kanten powder in water, boiling and setting it is far more common now and gives a similar result — but that is this dish imitated with the ingredient this dish produced. For the powder route, use 8g per litre of water. Seaweed-extracted jelly keeps a faint sea note and is slightly less clear.
Freezing it to make kanten. Leave set tokoroten outside on winter nights and let it thaw by day, over and over, and the water leaves it and a light white block remains. That is kanten, and the mechanism is exactly the one that makes the hwangtae in hwangtaeguk — ice crystals tear the structure and the meltwater runs out through the holes they leave. It was found by accident in seventeenth-century Kyoto, and yokan exists because of it.
The Kansai brown-sugar version: kuromitsu syrup and roasted soybean flour instead of vinegar soy, which makes it a dessert. Same jelly, a completely different dish — possible precisely because the jelly itself tastes of nothing.
Against dotori-muk: acorn muk is set starch, so it is opaque, soft, and takes up seasoning. Tokoroten is a seaweed polysaccharide, so it is firm, translucent and takes up nothing. Cut into strips and dressed is the same idea; whether the dressing gets inside is not.
Strand size: 5mm is standard. Thicker and it eats like a block of jelly; thinner and it breaks as you pick it up.
It is summer food. Edo street food in the hot months, and even before refrigeration it set at room temperature because agar's setting point is around 40°C. That property is what made it a summer trade.

Tips

The washing is half the recipe. Tengusa carries sand and shell, and washing it carelessly means grit in the finished jelly.
Strain it hot. This is the only step here with an order to it. Let it cool even a little and it begins setting in the cloth, and the yield falls off sharply.
Judge the extraction with a spoon, not a clock. The liquid should be slippery enough to leave a thin film on the back of one. Still watery, give it another twenty minutes.
Agar has to be boiled to dissolve. Gelatine loses its power if boiled and agar demands it — yokan sets that contrast out.
Never dress it ahead. This jelly absorbs nothing, so an early dressing does not soak in, it just collects underneath. The exact opposite of oden, which draws broth into itself as it cools.
Leftovers keep two days in the fridge, though they weep a little water. Melt them down and reset them and they come back as new — which gelatine could not do.