Arame and Hijiki: Japan's Black String Seaweeds — How to Cook Them Safely

Open a Japanese pantry and somewhere behind the kombu and wakame you will find two bags of what look like black thread: arame and hijiki. They are the workhorse brown seaweeds of everyday home cooking — simmered with root vegetables, tossed through rice, scattered over tofu — and they are also the two seaweeds about which Western eaters have the most questions, one of them entirely fair. Hijiki carries a genuine arsenic caveat; arame mostly carries its reputation. This guide sorts the two apart: what they are, how to cook each one, and how to think about the safety question with neither panic nor complacency.

Two seaweeds, often confused

Arame (Eisenia bicyclis) is a kelp relative harvested wild on Pacific rocky coasts and, increasingly, cultivated. It is cut into fine shreds and traditionally steamed before drying, which softens both texture and flavour. Rehydrated, arame is dark brown-black, tender, and notably mild — the friendliest entry point in the whole brown seaweed family, with a slight sweetness and almost no oceanic edge.

Hijiki (Sargassum fusiforme, now often classified as Hizikia fusiformis) grows on wild rocky shores around Japan, Korea and China. Thicker, blacker strands, simmer-dried at harvest rather than steamed. Its flavour is stronger — earthy, mineral, distinctly marine — and its texture heartier. It has been a staple simmer dish (hijiki no nimono) in Japanese home cooking for generations.

They are not interchangeable in cooking time or flavour strength, and one crucial difference — arsenic content — means they should not be interchangeable in your rotation, either. More on that below.

Preparing both: soak, rinse, simmer

Prep is identical up to a point. Both are sold dried and expand dramatically:

1. Soak in abundant cool water: arame 10–15 minutes, hijiki 20–30 minutes. They triple in volume or more — a 30 g bag becomes a heaped bowl.
2. Rinse well in a sieve, lifting the seaweed with your fingers so any sand settles out. The soak-and-rinse step is not only about grit: it draws away a share of the water-extractable compounds, which matters for hijiki in particular.
3. Drain well. Arame is now ready to use either raw in salads (it is mild enough) or simmered fifteen minutes for a fuller flavour. Hijiki essentially always wants a simmer — twenty to thirty minutes in seasoned liquid — both for taste and texture.

Seasoned simmer liquid for either: dashi or water with soy sauce, a little sugar or mirin, and sake — roughly 4 tablespoons soy, 1 tablespoon each sugar and sake to 400 ml liquid. This is the nimono base.

Cooking with arame: three everyday paths

Arame and vegetable sauté. Soften a sliced onion and a carrot in sesame oil, add soaked arame and a splash of the nimono seasoning, cook five minutes. Finish with toasted sesame. Sweet, faintly nutty, and the dish that converts people who "don't like seaweed."

Arame rice. Fold soaked arame through freshly cooked rice with a tablespoon of soy and a handful of edamame. It seasons the whole pot without dominating it — good lunch-box rice, good onigiri rice.

Arame salad, no cooking. Soak, rinse, squeeze and dress with rice vinegar, a little soy and sesame oil against shredded cabbage or cucumber. Because arame is steamed at harvest, it is tender enough to eat straight from the soak — genuinely rare among brown seaweeds — which makes it the lowest-effort seaweed in the pantry. If you like the cold-dressed approach, the same dressing logic as our wakame salad applies.

Arame keeps a year or more dried; cooked dishes hold three days refrigerated.

Cooking with hijiki: the classic nimono

The defining hijiki dish, worth making properly once:

1. Soak 30 g hijiki 25 minutes; rinse and drain.
2. In a saucepan, fry a matchsticked carrot and 100 g sliced fried tofu pouch (abura-age — optional but traditional) in a little oil.
3. Add the hijiki with 400 ml dashi, 4 tablespoons soy sauce, 1 tablespoon each of sugar, mirin and sake.
4. Simmer twenty minutes until the liquid is nearly gone and the strands are glossy.

Serve at room temperature as a side dish; it is one of the classics of Japanese home cooking. Add shelled edamame at the end for colour. Hearty, savoury-sweet, deeply mineral — you taste immediately why this dish survived centuries.

So with a dish this good, why the caution labels?

The hijiki question, honestly

Hijiki accumulates inorganic arsenic from seawater at levels materially higher than other food seaweeds — this is the honest core of the story. Inorganic arsenic is the form of concern (distinct from the largely benign organic arsenosugars found in most seafood), and food safety agencies in the UK, Australia and New Zealand, Canada, and Hong Kong have each tested hijiki and advised consumers against eating it; some advise choosing other seaweeds entirely.

What that means in practice, for a home cook making an informed choice:

• Occasional small servings are very unlikely to matter. The agency advice is conservative and aimed at cumulative exposure; a side dish of nimono a few times a year sits far from any meaningful risk threshold for most people.
• Hijiki should not be your everyday seaweed. If you eat seaweed several times a week — and this site would encourage you to — build the habit on other species, and treat hijiki as an occasional dish rather than a staple.
• Soaking and rinsing reduce, but do not eliminate, inorganic arsenic. Good prep helps; it is not a fix.
• Arame is a different picture. Testing in the same markets found arame's inorganic arsenic far lower, broadly in line with other commonly eaten seaweeds, and it is not subject to the same advisories.
• Pregnancy is the caution case. If you are pregnant, skipping hijiki is the simple, sensible call.

Our deeper guides on heavy metals in seaweed and the wider seaweed nutrition picture cover sourcing variation — water quality at the harvest site drives mineral load for every species.

Buying, and a sourcing note

Both keep a year or two in an airtight jar in the dark. Buy from sellers who name the harvest origin; Japanese and Korean domestic-market brands generally test to national standards. Hijiki is wild-harvested from intertidal rocks, a slow and seasonal fishery — smaller packets at higher prices than farmed seaweeds are the norm and the honest economics of a wild crop. If the arsenic question has you looking for substitutes, the closest flavour-and-texture stand-ins are shredded kombu simmered nimono-style, or sea spaghetti reduced well, or simply arame cooked the hijiki way with a longer simmer.

Key takeaways

• Arame (Eisenia bicyclis) is mild, steamed at harvest, and tender enough to eat straight from a ten-minute soak; hijiki (Hizikia/Sargassum fusiforme) is stronger, wild-harvested, and always wants a seasoned simmer.
• Soak and rinse both well; hijiki twenty-plus minutes, arame ten.
• Hijiki accumulates inorganic arsenic at levels that have led several national food agencies to advise against eating it — treat it as an occasional dish, not a staple, and skip it in pregnancy.
• Arame tests far lower and is not under those advisories; it is the sensible everyday choice of the pair.
• The classic hijiki nimono — soy, sugar, sake, carrot, abura-age — is worth cooking at least once to understand the tradition.

FAQ

Is hijiki banned anywhere?

Not generally banned, but food safety authorities in several countries — including the UK and Australia/New Zealand — advise consumers not to eat it based on inorganic arsenic testing, and import rules vary. It remains a legal, common food in Japan and Korea, where consumption is typically in small side-dish portions.

How much hijiki is too much?

No single serving of a traditional side portion is a concern for a healthy adult; the agencies' worry is regular, frequent consumption adding to lifetime inorganic arsenic exposure, which is cumulative. Keeping hijiki to occasional use — a handful of times a year rather than weekly — is the straightforward interpretation of the advice.

Does soaking hijiki remove the arsenic?

Partly. Soaking and rinsing in abundant water measurably reduces inorganic arsenic levels, and cooking in water you then discard reduces them further. It does not bring hijiki down to the levels of other seaweeds, so prep helps but is not a licence for daily eating.

Is arame the same species as hijiki?

No — they are different species from different seaweed families, which is exactly why their arsenic profiles differ. Arame is a kelp relative (Eisenia bicyclis); hijiki is a sargassum (Hizikia fusiformis). They look similar dried and are shelved together, which causes the confusion.

What can I substitute for hijiki in nimono?

Shredded kombu or sea spaghetti, simmered the same soy-sugar-sake way, get closest on texture and take the seasoning beautifully. Arame with a longer simmer is the milder option. None has hijiki's exact mineral depth, but all make an excellent nimono in their own right.