My entire experience of seaweed as food was the dried sheets in a supermarket and a health food shop selling powder in a tub. I had filed the whole category under recent wellness marketing.
That is close to the opposite of the truth, and eating it in places where it is traditional changed my view completely.
It is old, not new
Coastal populations across the world have eaten seaweed for as long as there is evidence of them.
Ireland, Wales and Scotland have continuous traditions. Japan and Korea obviously. Iceland, the Pacific islands, parts of South America, coastal China.
In several of those places it was a famine food and a staple simultaneously, which is a common pattern for things that are abundant and free.
Which means the current interest is a revival rather than an invention, and the recipes that exist in those traditions are considerably better than anything designed by a marketing department.
The varieties are as different as vegetables
The error underlying my dismissal. I had treated seaweed as one ingredient.
The category covers organisms as different from each other as a mushroom is from a cabbage, with completely different flavours, textures and uses.
Some are crisp and mild. Some are deeply savoury and used the way a stock ingredient is. Some are gelatinous and used as thickeners. Some are eaten fresh as a salad vegetable and are unrecognisable as the same category as a dried sheet.
Buying a tub of unspecified powder and concluding you do not like seaweed is like buying a tub of unspecified vegetable powder and concluding you do not like vegetables.
The savoury depth thing is real
The property that makes it genuinely useful in cooking rather than merely virtuous.
Several varieties are extremely high in the compounds responsible for savoury depth, which is why one of them is the foundation of an entire cuisine's stock.
Practically, a piece added to a pot of beans, a soup or a braise adds a background savouriness without adding any identifiable seaweed flavour. Most people cannot tell you what has been added and can tell the difference.
This is the use I have adopted permanently and it is the least exotic possible application.
The traditional preparations I encountered
The ones that changed my mind, all eaten in places where they are ordinary.
A dark preparation cooked slowly for hours until it becomes a thick savoury paste, eaten with bread or with a cooked breakfast. Unrecognisable as seaweed and extremely good.
Fresh salads of crisp varieties dressed with acid and oil, which taste of the sea in a clean way rather than a fishy one.
Dried and toasted varieties crumbled over food as a seasoning, which is essentially a salt substitute with more going on.
And a flatbread with seaweed worked into the dough, which I would not have identified.
Foraging it yourself, with caution
Possible and requires more care than people assume.
The main considerations are water quality, since seaweed concentrates what is in the water, including pollutants and heavy metals. Harvesting near outfalls, harbours, industry or agricultural runoff is a poor idea.
Identification matters less than with fungi, since there are very few dangerous seaweeds, and it still matters for palatability.
Cutting rather than pulling, leaving the holdfast so it regrows, is the standard practice and is what distinguishes sustainable harvesting from stripping a shore.
And in many places there are legal restrictions on commercial or even personal harvesting, and traditional rights that predate any modern regulation. Asking locally is both practical and courteous.
The iodine caution
The one genuine health consideration and it runs opposite to the marketing.
Some seaweeds, particularly certain brown varieties, contain very high concentrations of iodine — high enough that regular substantial consumption can affect thyroid function.
This is a documented issue rather than a theoretical one, and it is the reason some countries have issued guidance about consumption limits for particular species.
Anyone with a thyroid condition should be getting advice from somebody qualified rather than from a food article, and that applies particularly to the concentrated supplement forms rather than to eating it as food occasionally.
Where I ended up
Using a piece of the savoury kind in stocks and braises regularly, which is a small permanent change I would recommend to anybody.
Eating the traditional preparations when I am somewhere they are traditional, which is where they are best and where they make sense.
And ignoring the powders and supplements entirely, which is where I started and for once was right.
Buying it
Practical guidance since the retail landscape is confusing.
Dried whole seaweed from a supplier that names the species and where it was harvested is the thing to buy. It keeps almost indefinitely, costs little, and is what the traditional recipes assume.
Powders and supplements are where the price and the marketing are, and where the iodine question is most relevant.
Fresh seaweed is available near where it is harvested and is worth trying when you see it, since it is a different ingredient from the dried version rather than a fresher one.
The specialist shops serving the cuisines that use it most are consistently cheaper and better stocked than any health food retailer.