Gulfweed

Sargassum fulvellum

Alginate and fucoidan · the brown alga in Jeju mom-guk

Gulfweed is a brown alga that fastens to rock along the shore, known on Jeju as mom. Mom-guk, the soup made by dropping it into the broth from boiled pork, was cooked in a great pot for every village feast. Small air bladders along the stem hold it upright underwater, and those bladders are what separate it from kelp and sea mustard. It grows through winter into spring, so from February to May the fresh weed appears in traditional markets, blanched for a vinegared salad or dropped into soup. The brown fronds turn bright green the moment they hit boiling water, because the pigment of a brown alga changes with heat. The Donguibogam lists it in the Vegetable section as 海藻, records the Korean name as mal, and notes that it grows in the sea and is gathered on the seventh day of the seventh lunar month and dried in the sun. It gives a cold nature, a bitter and salty taste and no toxicity, adding that some call it slightly toxic.

Year-Round Calendar

Harvest

Where It Grows

Main producer Major producer Latitudes at 10–20℃ Zoom and pan to explore · temperatures are rough zonal averages

Main producer Gathered from the shore rocks of Jeju and the south coast, with some of it grown tied to ropes. On Jeju it is called mom. Harvest February, March, April, May
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Major producer Along the coasts of Shandong and Fujian, gulfweeds are both gathered and farmed.
Major producer It grows on the shore rocks of the Honshu and Kyushu coasts and is handled alongside hijiki, a relative in the same group.

Gulfweed (Sargassum fulvellum) is a species of the northwestern Pacific, found along the coasts of Korea, China and Japan, and production is in practice limited to those three countries. The genus Sargassum contains many species, and two of them are not this one: gwaengsaengi mojaban (S. horneri), which has lately been drifting in from the East China Sea in great quantity and piling up along the shore, and the floating mats of the Sargasso Sea in the Atlantic. This map should not be read as the range of those.

Optimum water temp.: 10~20℃
Range: 5~25℃
Hardiness: Not applicable
Day length: Not applicable

What sets the growing season is water temperature, not air temperature. Growth starts in late autumn as the water cools, runs longest through the winter and early spring, when the sea sits at 10~15℃, and by early summer, once it passes 20℃, the fronds rot and drop away. The plant puts no roots into soil; it fastens itself to shore rocks and gravel below the intertidal zone with a holdfast.

In Korea Coastal areas

Jeju and the south coast of South Jeolla — Wando and Jindo — are the centre of production. The season runs from February to May, and the weed is cut from the shore rocks, with the holdfast left in place.

How to grow

Light: Sunlit shallow water. It fastens to shore rock and cobble below the intertidal zone
Soil and depth: Nothing is planted in soil. A holdfast grips the rock in place of roots, and the nutrients come from seawater
Spacing: Choosing it — take thick, straight stems with the bladders unburst. Limp, yellowing fronds are old
Watering: Preparing it — swirl it through several changes of cold water to clear sand and salt. Blanch fresh weed straight after washing
Feeding: No feeding. It lives on the nutrient salts dissolved in seawater
Harvest: The season is February to May. Cut weed growing on shore rock, leaving the holdfast so it regrows next year. Check first that the area is open to gathering

What makes the difference. Storing — blanch, squeeze out the water, portion it and freeze. Dried weed goes into a sealed container once fully dry and is kept somewhere cool

Why this one is harder. Never go out onto shore rocks without knowing the tide. In many places the way back is cut off as the water rises, and seaweed on wet rock is dangerously slippery. Buying it is the safer route: fresh weed appears in traditional markets on the south coast and on Jeju through spring

Common problems

Sand and encrusting life You will see Sand caught between the fronds, small shells or moss attached What to do Rinse through several changes of cold water and pick off anything visible by hand
Spoilage You will see The colour yellows, the surface turns slimy and the smell sharpens What to do Discard it. Blanch fresh weed the day you buy it and keep none over
Oil and litter You will see An oily film or scraps of plastic in a pile washed ashore What to do Do not pick up anything washed ashore. Take only weed still growing on rock

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 — haejo (海藻). The Donguibogam lists it in the Vegetable section as 海藻 and gives the Korean name as mal. It records a cold nature, a bitter and salty taste and no toxicity, adding that some call it slightly toxic. It grows in the sea, the entry says, and is gathered on the seventh day of the seventh lunar month and dried in the sun. What an old medical text wrote differs from how it is judged today.

Polysaccharides of brown algae. Repeated analyses report polysaccharides such as alginate and fucoidan isolated from the cell walls of brown algae. Alginate is also used in food manufacture to set viscosity. This is a compositional record.

Told apart by the bladders. Sargassum species carry air bladders along the stem that hold them upright underwater. Those bladders are the clearest mark separating them from kelp and sea mustard. This is a record of form.

Nutrition

Alginate (structural material of the cell wall) — the viscous polysaccharide characteristic of brown algae
Fucoidan (reported in brown algae) — a sulfated polysaccharide
Fucoxanthin (the pigment behind the brown colour) — a carotenoid of brown algae whose colour shifts with heat
Iodine (gathered from seawater) — a mineral abundant in seaweed

The colour changes on blanching Brown fronds turn bright green as soon as they meet boiling water. The fucoxanthin that carried the brown shifts with heat and the chlorophyll beneath it shows through. Lift it out the moment the colour turns and rinse it in cold water to keep the texture.

Alginate and the slippery feel The cell wall of a brown alga carries alginate, which is what makes it feel slippery to handle. Soaking and rinsing repeatedly takes down both the salt and that slipperiness. This entry stays with the compositional record.

Fucoidan Fucoidan, a sulfated polysaccharide, is reported in brown algae. Research continues, but it mostly uses extracted and purified material, a different setting and quantity from gulfweed eaten as a side dish.

Iodine Seaweed is high in iodine. Levels differ widely by species, by the water it grew in and by how it is prepared, so no single figure will stand. Anyone who has to manage iodine intake should discuss how much seaweed to eat with a clinician.

Pairings

○ Pork broth — mom-guk — Jeju mom-guk is blanched gulfweed simmered in the broth from boiled pork. The weed thickens a rich broth and pulls the flavour together. Buckwheat flour is sometimes stirred in to set the body.

○ Vinegared chilli paste — Shake the blanched weed dry and dress it with vinegared chilli paste. The acidity softens the sea smell and holds the colour. Shredded radish or cucumber spreads the moisture evenly.

○ Rinsing repeatedly in cold water — Half the preparation is rinsing. Swirl it through several changes of cold water and the sand caught between the fronds comes out with the salt. Skip this before blanching and the grit is still there in the finished dish.

△ Picking up what washed ashore — Gulfweed piled on a beach is not eaten. Through winter and spring, drifting Sargassum horneri washes ashore in bulk; it has been adrift a long time, has begun to spoil, and comes mixed with oil and litter. Edible gulfweed is cut in season from rock it is still growing on.

△ Gathering without permission — Inshore waters are often held under a village fishery right, and taking seaweed without permission causes trouble. Permitted areas and seasons vary by region, so check first, and never go out onto shore rocks without knowing the tide.

△ Soak it, and throw the blanching water away — Hijiki, in the same genus, is high in inorganic arsenic, and several countries advise soaking it and discarding the blanching water. Treat gulfweed the same way: soak, rinse and pour the blanching water off. Anyone who has to manage iodine intake should discuss how much seaweed to eat with a clinician.

Varieties

Gulfweed (Sargassum fulvellum) (gathered) — The group called mom on Jeju, used in mom-guk and vinegared salads
Hijiki (Sargassum fusiforme) (gathered) — Another species in the same genus, with plump side branches, cooked into rice
Devil weed (Sargassum horneri) (gathered) — The drifting species that washes ashore in winter and spring. Nothing washed up is eaten

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