By Harold McGee
Seaweed is a very general term for large plants that inhabit the oceans. Nearly all ocean plants are algae, a biological group that has dominated the waters for close to a billion years, and that gave rise to all land plants, including those that feed us. There are more than 20,000 species of algae, and humans have enjoyed many hundreds of them. They’ve been especially important foods throughout coastal Asia, in the British Isles, and in places as different as Iceland and Hawaii, where they’re among very few native edibles. The Japanese use seaweeds as wrappers and to make salads and soups; in China they serve as a vegetable; in Ireland they’re mashed up in porridge and thicken desserts. Most seaweeds have a richly savory taste and a fresh aroma reminiscent of the seacoast, which in fact they help to perfume. Many are good sources of vitamins A, B, C, and E, of iodine and other minerals, and when dried may be a third protein. Seaweeds are abundant, renew themselves rapidly over a life span of one or two years, and are easily preserved by drying. In Japan, where they’ve been cultivated since the 17th century, the farmed production of the seaweed used to wrap sushi is more valuable than the harvest of any other aquacultural product, including fish and shellfish.