Sea Mustard (Wakame)

Undaria pinnatifida

Alginate, fucoidan and iodine · a brown seaweed lifted from winter into spring

Sea mustard is a brown seaweed and the alga that reaches the Korean table most often — in soup, in cold soup, in dressed salads. A thick midrib runs up the centre while the blade cuts deeply into pinnate lobes, and the frilled, folded part near the holdfast is the sporophyll. It is lifted from the sea between winter and spring, so fresh fronds appear only in those months; the rest of the year it comes dried or salted. Dried fronds swell several times over in water, which is how one handful fills a whole pot. The slippery feel comes from polysaccharides such as alginate and fucoidan, and the brown colour from the pigment fucoxanthin. Brown algae concentrate iodine from seawater and sea mustard runs high in it, so anyone under care for a thyroid condition does better to settle the amount with their doctor. The Donguibogam lists it in the Vegetable section as 海菜 and records the old Korean name as meoyuk, the archaic form of the modern word for the plant.

Year-Round Calendar

Sowing

Harvest

Where It Grows

Main producer Latitudes at 10–15℃ Zoom and pan to explore · temperatures are rough zonal averages

Main producer The world's largest producer of sea mustard. The Shandong and Liaoning coasts are the center of it.
Main producer Seedlings are fastened to ropes and strung out in the sea to grow. Wando and Jindo in South Jeolla, and Gijang in Busan, are the known areas. Harvest December, January, February, March, April
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Main producer The Sanriku coast and Naruto in Tokushima are the known areas.

It is native to the northwest Pacific along the coasts of Korea, Japan and China, and commercial production to date has been almost entirely confined to those three countries. It has spread on ships' hulls and in ballast water to France, New Zealand, Argentina and elsewhere, but in those places it is treated as an invasive species rather than a crop, so they are not counted here as producing regions.

Optimum water temp.: 10~15℃
Range: 5~20℃
Hardiness: Not applicable
Day length: Not applicable

What sets the growing season is water temperature, not air temperature. The seedlings go into the sea in autumn, as the water falls below 20℃; growth is strongest from winter into early spring, when it hovers around 10℃; and the plant breaks down in early summer, once the water rises past 20℃.

In Korea Coastal areas

South Jeolla south coast (Wando, Jindo)

Sowing

Harvest

Busan and South Gyeongsang coast (Gijang)

Sowing

Harvest

How to grow

Light: Not a crop anyone grows. It is lifted from coastal water between winter and spring, and water temperature rather than sunlight fixes the season
Soil and depth: Nothing is planted in soil. It grows attached to coastal rock, or on seeded ropes suspended in the sea
Spacing: Farm ropes are set apart so the current runs between them. Fronds grown where the current is strong come up thicker
Watering: Preparation is where water matters. Rinse fresh fronds under running water; rinse salted fronds several times in cold water to draw out the salt
Feeding: No feeding. It lives on what is dissolved in seawater
Harvest: Buy on colour and thickness. Choose dried fronds that are an even, near-black deep brown with few crumbs and little white powder. Choose fresh fronds with springy blades and the slipperiness still on them

What makes the difference. Keep dried fronds sealed somewhere cool and dark. Use rehydrated fronds the same day, and refrigerate any remainder squeezed dry

Why this one is harder. Several seaweeds carry similar names, and the same name sometimes attaches to different species. Sea mustard is told from kelp by the thick central midrib and the deeply cut pinnate blade — kelp blades are broad and uncut

Common problems

White salt crystals You will see A white powder sits on the surface of salted fronds What to do It is dried packing salt. Rinse several times in cold water and soak to draw the salt out before use
Going slack You will see Rehydrated fronds turn limp and tear in the hand What to do They were soaked too long. Soak briefly in cold water and add them to soup at the end for a short simmer
Damp dried fronds You will see The dried fronds feel damp and the smell turns flat What to do They have taken up moisture. Store sealed with a desiccant somewhere cool and dark, and discard anything whose smell has changed

This page describes how a crop is grown and used. It does not claim health effects for any food, nor is it intended to prevent or treat disease. Component and study notes are references only and do not mean the same result occurs in people. Consult a medical professional about health concerns.

Health Benefits

The old record — haechae (海菜). The Donguibogam lists it in the Vegetable section as 海菜 and records the old Korean name as meoyuk. It gives a cold nature, a salty taste and no toxicity. It says the plant grows in the sea and its colour is a true blue-green, and that once gathered and dried the colour turns purple, so it also carries the name 紫菜. That old word meoyuk is the ancestor of the modern Korean name for the plant. This is a historical medical record and differs from modern medical judgment.

Polysaccharide analyses in brown algae. Polysaccharides such as alginate and fucoidan have been isolated from sea mustard and other brown algae in repeated analyses. The results account for the slippery texture and for the way the broth thickens. These are compositional analyses and have nothing to do with preventing or treating disease.

The spread in iodine figures. Compositional analysis confirms both that brown algae concentrate iodine from seawater and that the amount varies widely with origin, plant part and drying. That is why no single number settles the question even for one species.

Nutrition

Alginate (structural material of the blade and stipe cell walls) — a polysaccharide particular to brown algae
Fucoidan (in the slippery mucilage) — a sulphated brown-algal polysaccharide
Iodine (high among edible seaweeds) — a mineral concentrated from seawater
Fucoxanthin (the pigment behind the brown colour) — a carotenoid pigment of brown algae

How far dried fronds swell Dried sea mustard takes up water and swells several times over. That is why a handful dropped into a soup ends up filling the pot. Soak briefly in cold water; a long soak turns it slack and the bite disappears. When reading a composition table, check whether the figures are on a dried or a rehydrated basis before comparing anything.

Alginate and fucoidan The slippery feel comes from polysaccharides such as alginate and fucoidan. Alginate builds the cell walls of brown algae; fucoidan is a sulphated polysaccharide. Both dissolve out and thicken the broth slightly. This entry stays with the compositional record.

Iodine Brown algae concentrate iodine from seawater, and sea mustard runs high in it. Analyses report wide variation with origin, plant part and degree of drying. Since it appears in soup so often, anyone under care for a thyroid condition does better to settle the amount with their doctor.

Calcium, potassium and fibre Sea mustard carries calcium, potassium and soluble dietary fibre. Dried fronds have lost most of their weight as water, so per-100g figures read high while the dried quantity actually used in one meal is very small. Not carrying the table's order of magnitude straight into a single serving is the trick to reading it.

Pairings

○ Beef and perilla oil — Rehydrate the dried fronds, fry them in perilla oil, then pour in water and simmer — the base of miyeok-guk. Frying beef alongside deepens the broth. A pinch of salt during the frying keeps the fronds from breaking down.

○ Cucumber and vinegar — cold soup — Rehydrated fronds with shredded cucumber, vinegar and cold water. The acidity covers the marine note. Boil the water and chill it beforehand for a cleaner finish. Cucumber

○ Garlic and sesame oil — stir-fried stipe — Rinse salted stipe strips several times in cold water to draw out the salt, then stir-fry hard with garlic. Long cooking draws water and turns them limp, so keep it brief. Garlic

△ Iodine — scaling the amount up — Sea mustard runs high in iodine among edible seaweeds, so avoid scaling up to several bowls of soup a day. If a thyroid consultation or test is coming up, settle the amount and the timing with your doctor. An ordinary serving with a meal is not the issue.

△ Using salted fronds unrinsed — Salted sea mustard has been packed in salt, and using it straight throws the seasoning off. Rinse several times in cold water, soak about ten minutes to draw the salt out, then squeeze dry. Adding salt to a soup that already holds unrinsed fronds cannot be undone.

△ Keeping rehydrated fronds — Rehydrated sea mustard spoils quickly at room temperature. Use it straight away; if any is left, squeeze it dry, refrigerate it and use it within the day. Dried fronds keep a long time sealed somewhere cool.

Varieties

Wild rock-grown fronds (origin) — Lifted from fronds grown on coastal rock. Thick-bladed and slow to break down in a long simmer
Farmed fronds (farmed) — Grown on seeded ropes suspended in the sea. Most dried sea mustard on the market
Sporophyll (miyeok-gwi) (part) — The frilled, folded part near the holdfast. Crunchy, and dressed as a dish of its own
Stipe strips (part) — The thick midrib split and salted. Mostly stir-fried

Source: Donguibogam, Vegetable Section 海菜 · National Institute of Fisheries Science · Korean Food Composition Table