Seaweed: Should We Be Eating More OF It?

The ancient food that asks almost nothing of the land, the water, or the planet.

It is the early morning golden hour. The tide has just finished pulling back from the Galloway coast, and the air smells salty, slightly grassy, faintly sweet.

An old man is crouched over a rockpool, knife in hand, working a dark leathery frond free from a boulder as the small waves continue to recede. He could easily pull out the entire frond, as he has watched excited tourists do, but he has spent his whole life living by the coast foraging for seaweed and has acquired a deep understanding of the sea and its secrets. With one hand grasping the frond, he slowly and skilfully cuts close to the base leaving the holdfast clinging to the rock so the algae can grow back and he may return for another harvest. By lunchtime his small cutting will be curling and crackling in a hot pan and will taste very much like bacon.

“It is a simple and nutritious ingredient,” the old man writes to his grandchildren in the city when they ask what he eats for lunch in his tiny coastal village. “It requires no irrigation, no fertiliser and no greenhouse; simply rocks, cold seawater and sunlight. It’s about as old a way of gathering food as humans have ever come up with and it might also be one of the more useful ones we’ve forgotten.”

The old man is not wrong.

The coastal communities of Japan, Ireland, Chile and the Pacific Northwest have carefully harvested seaweed from their shorelines for thousands of years. Japan has continuously harvested seaweed making it a central ingredient to much of its cuisine, as generations of cooks became skilled at extracting delicious umami flavours from many varieties. In Europe, seaweeds were once commonly consumed till the 1800s when they were eventually relegated to famine food or animal feed.

Today, as the food industry looks increasingly towards plant-based ingredients to address climate change and global food security, seaweed is drawing serious attention for its nutritional density, versatility, low cost and ease of production.

Chefs and food scientists are looking at more ways to revive this inexpensive and highly nutritious algae, using their skill and techniques to create interesting dishes. The more we look towards seaweed, the clearer it appears it could save our planet.

Three Categories: Thousands of Species

The ocean contains an incredible variety of algae also known as aquatic vegetation or marine macro-algae, which are divided into three categories by colour: brown algae (Phaeophyta), red algae (Rhodophyta) and green algae (Chlorophyta). Each category encompasses thousands of species with distinct habitats, flavour profiles and culinary applications.

The scale of what’s out there is startling. The UK alone has over 700 species in its shallower waters, of which only around 20 are harvested for food. According to forager Mark Williams of Galloway Wild Foods, there are no toxic seaweed species in UK coastal waters, making the coastline a vast and relatively untapped wild larder, as long as foragers are mindful of water quality and pollution.

There is tremendous diversity in what the various species of seaweeds tastes like and what they can be used for in the kitchen.

Brown Algae: Giants of the Seaweeds

Brown algae are the biggest and fastest-growing seaweeds, thriving in nutrient-rich, fast-moving cool waters between 6°C and 14°C. They flourish along the Pacific coast of North America, around Japan, Korea, Chile, Norway and the British Isles.

Giant kelp forests rank among the most productive ecosystems on earth growing up to 60 centimetres a day which is faster than most bamboo, sheltering an extraordinary biodiversity of ocean life.

Kelp is used a great deal in Japanese and Korean cuisine; it is salty, faintly sweet and nutty and deeply savoury with a deep umami character that intensifies to a roasted smokiness when dried making it valuable for soups, stews and seasoning.

Popular varieties of brown algae include Kombu and Wakame.

Kombu has been harvested for thousands of years in the icy waters off Hokkaido, Japan. It is the cornerstone of Japanese cuisine and the primary component of dashi stock. It was kombu that food scientist Kikunae Ikeda used in 1908 when he first identified and named umami as a distinct taste, driven by its exceptionally high levels of naturally occurring glutamates. Kombu is mildly salty with a clean, earthy richness.

Wakame prefers slightly warmer, shallower coastal waters and is cultivated extensively in Japan, Korea, France and Ireland. Its flavour is subtly salty with a silky texture, well suited to miso soups and salads.

Red Algae: The Widest Variety

Red algae encompass the widest variety of culinary species and require less sunlight than other categories, allowing them to thrive in deeper intertidal zones and rockpools.

Popular varieties are Nori, Dulse and Irish Moss.

Nori belongs to this group and is the most technically processed of all seaweeds. Cultivated in Japan since at least the seventeenth century, most nori today is farmed in the calm coastal waters of Japan, Korea and China. It is prized for being rich in umami components with three types of amino acids, including glutamic acid which provides savoury depth. It is used for wrapping sushi, onigiri and as seasoning in many Japanese dishes. Top-grade nori is identified by its dark lustre, melt-in-the-mouth texture and deep, sweet savouriness.

Dulse is found on rocky Atlantic shorelines from Iceland and the Faroe Islands to Ireland, Scotland, the East Coast of America and Canada as it can tolerate more turbulent intertidal conditions than most species. Its intensely savoury, smoky, bacon-like flavour when pan-fried makes it valuable to chefs developing plant-based alternatives to smoked meats.

Irish moss is used for its carrageenan content and has been harvested for centuries along the coastlines of Ireland and Britain where it served as both famine food and medicinal remedy. Largely flavourless when processed, it functions primarily as a natural thickening and gelling agent in plant-based milks, desserts and food manufacturing.

Green Algae: The Delicate Seaweeds

Green algae is the smallest category and they are usually found in intertidal zones, rock-pools and shallow coastal waters worldwide.

Sea lettuce grows across nearly every coastline on earth and is farmed on suspended rope nets and in land-based aquaculture tanks in Scandinavia, California and Asia. Its flavour is fresh, grassy and lightly salty and its is most often used raw in salads or as a garnish.

Sea grapes prefer warmer waters, they are found in the shallow tropical waters of the Indo-Pacific, particularly around Okinawa, the Philippines, Vietnam and Indonesia. Sea grapes are cultivated in trays or nets in clean seawater. Their delicate small bead-like clusters burst with a clean, salty pop on the palate, reminiscent of caviar and are highly prized in Japanese and Southeast Asian cuisines for their flavour and visual impact. They grow rapidly and can yield more than an astonishing 30 tonnes per hectare annually.

Tasting seaweeds

Most people are familiar with nori on maki rolls but are less familiar with other varieties. Try these four seaweeds to get an idea of their different flavours.

• Kombu – has a clean broth-like flavour with a little saltiness. To make a simple broth, simmer on the lowest heat in water with a few shitake mushrooms for 15 minutes.
• Wakame – has a silky texture and slight sweetness. For an easy salad, soak for around 10 minutes to rehydrate then dress with rice vinegar and toasted sesame seeds.
• Dulse – has a smokey, almost meaty flavour. For a quick snack or simple garnish, pan fry in a little oil for about a minute till it crisps up.
• Nori (toasted) – dissolves on the tongue, slightly sweet. As it is already processed, it can be eaten straight from the packet.

Tide to Table: How Seaweed Is Produced

How seaweed is processed varies enormously by species and its intended use.

At its simplest, seaweed is washed and sun-dried, which concentrates flavour and boosts vitamin D.

Wakame is blanched immediately after harvest transforming it from brown to bright green before it is salted or freeze-dried for storage and later rehydrated.

Kombu takes longer, it is sun-dried for up to two years to develop the concentrated glutamates that give it its distinctive flavour for dashi, or worked further into tsukudani or oboro kombu flakes.

Nori undergoes the most sophisticated processing of all seaweeds, using significant expertise. Spores are seeded onto nets in early autumn as water temperatures drop then submerged in sheltered bays, strung on bamboo poles or floated on rafts. Periodic air exposure at low tide keeps disease at bay. After roughly 45 days, once the fronds reach 15-20 cm, specialised boats harvest the crop mechanically. The earliest harvests, running through December, produce the finest quality with fortnightly harvests continuing until warming water ends the season in April. The raw seaweed is washed, minced to a fine pulp, pressed into rectangular moulds, dried, then toasted. It is a process almost identical to traditional Japanese paper-making, practised for over 300 years. What emerges is a paper-thin sheet with a delicate, faintly sweet oceanic flavour, a pleasant chewiness when fresh and a crisp intensity once toasted.

Beyond these processes, brown and red algae are industrially broken down into hydrocolloids that quietly appear across the food industry. Alginate made from brown algae stabilises ice cream and gels, carrageenan from Irish moss emulsifies plant-based milks and agar from red algae serves as one of the most versatile vegan gelling agents available. Korean and Japanese fermentation traditions also transform seaweeds into umami-rich sauces and pastes.

A Plant Source of Iodine

Nutritionally, seaweed is high in fibre, low in calories and fat and carries good amounts of calcium, iron, magnesium and potassium. It is also one of the few plant sources of iodine and an important one for vegans. Iodine is important for thyroid function and it’s difficult to maintain healthy levels on a pure plant-based diet as most sources are animal-derived. A diet which includes seaweed would solve this, though levels vary wildly by species and origin, for example kombu has the highest concentration of iodine compared with other seaweeds, so a tiny amount (⅛-1/10 of a teaspoon) would easily meet daily requirements.

Sustainability and Environmental Concerns

Few foods can match seaweed’s environmental record. It does not require watering, arable land, fertilisers nor pesticides. As it grows, it draws carbon dioxide and nitrogen out of the surrounding water easing local ocean acidification, while kelp forests sequester carbon at remarkable rates and provide habitat for fish, invertebrates and countless other marine organisms.

Yet these ecosystems are increasingly under threat. Warming ocean temperatures and nutrient-poor waters driven by El Niño patterns are taking a toll and aggressive sea urchin populations are suppressing kelp forest recovery along coastlines from California to Tasmania making their protection as ecologically urgent as the preservation of tropical rainforests.

On an industrial scale, significant concerns exist surrounding large-scale monoculture seaweed farming in China and South Korea, accounting for over 95% of global production. It raises the same concerns as monoculture farming on land where overly dense seaweed cultivations can block sunlight, reducing biodiversity, disrupting water flow thereby creating conditions for disease outbreaks. Professor Juliet Brodie of the Natural History Museum, one of the world’s leading authorities on seaweed aquaculture, states that well-managed cultivation can simultaneously improve livelihoods and restore marine ecosystems, provided biodiversity is prioritised over monoculture production.

The introduction of non-native seaweed species carries additional ecological risks, for example wakame escaped cultivation and is now considered invasive in parts of Europe and Australia, altering the local biodiversity. There’s also the problem of harvesting seaweed from polluted waters as seaweed easily absorbs heavy metals from polluted coastal water, which makes regulation near industrial coastlines a genuine concern.

The processing industry leaves its own trail of considerable biomass waste once agar, carrageenan and alginate have been extracted, although it is increasingly being repurposed as animal feed, biofuel and compost.

Meanwhile, wild harvesting in Ireland, Scotland and Iceland requires careful management to prevent over harvesting and disruption to coastal ecosystems.

Two Easy Seaweed Recipes

Try these two easy seaweed recipes for Kombu Dashi (a vegan stock) and Dulse ‘Bacon’ Bits. Both use dried seaweed which keeps for months in a cupboard.

Kombu Dashi: the stock of Japanese cooking

Two ingredients: a piece of dried kelp and a pan of cold water. Warm it gently on lowest heat and in ten minutes you will have a clear, golden, deeply savoury stock that forms the base of many Japanese dishes from miso soup to ramen broth. It’s also an easy way to taste this umami flavour as kelp is the seaweed Kikunae Ikeda was studying when he named the taste.

Dulse “Bacon” Bits - the one nobody believes until they try it

Fry a few pieces of dried dulse in a little oil on a hot pan for a minute and they will curl, crisp, and turn smoky. It will still have a seaweed texture but a smokey meaty flavour that is often compared with bacon and the reason plant-based chefs keep reaching for this particular seaweed. Scatter it over avocado toast, baked potatoes or scrambled tofu.

So, Should We Eat More Seaweed?

From the kombu broths of Hokkaido to dulse replacing bacon for vegan dishes, seaweed’s range on the plate is matched by its benefits for the planet. The entire British coastline alone has such a tremendous supply of inexpensive and nutritious aquatic vegetables which could contribute to a healthy diet. If farmed and harvested responsibly then processed with care, seaweed could become a pillar of a more sustainable food system, one that requires almost nothing of the land, the freshwater, or the fertiliser the rest of our food depends on.