Uses of Kelp

Cast kelp or ‘tangle’ has been utilised by generations of Scots industrialists, farmers and crofters for manufacturing and agricultural purposes, especially in the Highlands and Islands.

The very name ‘kelp’ was first coined to mean the ash produced after tangle burning, and only later came to refer to the seaweed itself. This ash was first produced on a large scale, particularly in Orkney and the Western Isles, in the early 18th century; its high potash and soda content were used in glass and soap manufacture. At its peak, between 1780 and 1830, the industry employed several thousand people. The bulk of the ash was exported south for further processing. With the discovery of other sources of potash and soda, the industry declined.

It revived on a smaller scale, however, with the discovery in the 19th century that iodine could be extracted from laminarian ash, a practice which continued until the 1930s. At that time imports of cheaper iodine extracted from Chilean nitrate deposits ended the Scottish kelp industry.

In recent times several thousand tonnes of dried tangle have been collected each year by crofters in the Western Isles and Orkney. Cast kelp stipes are gathered from the foreshore, particularly after the wild Atlantic storms which affect the island groups, and are stacked on huge drying racks until ready for transportation to the mainland. In addition, the egg wrack, Ascophyllum nodosum, has been harvested from the shore. Seaweed collectors work on a self-employed basis, and the pattern of work fits in well with traditional crofting activity. These seaweeds are used, not for iodine or potash production but for the extraction of ‘alginates’.

Alginates are chemicals with a wide range of applications in the food, textile, pharmaceutical and other industries. These uses depend on their gelling and emulsifying properties. The chemicals are found in products as diverse as tomato ketchup, postage stamps, medical dressings and beer (alginates are added to aid head retention). World-wide, over 0.5 million tonnes of seaweed per year is used in alginate production, much of it giant kelp, Macrocystis pyrifera, from California or cuvie, Laminaria hyperborea, from Norwegian coastal waters.

Storm-cast kelp is also collected by farmers and crofters for fertilising the soil. In the Western Isles it is ploughed into the relatively nutrient-poor sandy soils of the machair, enhancing the growth of arable crops.