Rice wine vinegar (optional)
Lime juice (optional)
Tabasco sauce (optional)
The big thick kelps such as Laminaria digitata, but potentially also more mature sugar kelp and dabberlocks are, from my personal perspective on edible seaweeds, pretty indigestible and have a tendency to be tough when compared to sea lettuce, gutweed and that traditional Japanese favourite wakame.
The slow cooking process used here is a good method of making the tougher kelps usable. Even so, I would seek out the very youngest specimens and the most tender growth for this recipe - simply because they will require less cooking and be far more palatable.
The way I view this kelp relish is being something akin to the lime pickle which appears as an accompaniment to Indian food (particularly if you use dark soy sauce).
In this case, however, the relish is more of an accompaniment to fish, or as an additional item for salads.
The optional vinegar, lime juice and chilli sauce ingredients listed above provide you with three alternative twists to the relish - one tart, one tangy, one spicy.
The first time you experiment with this I suggest working on the plain soy sauce version, and then simply trialling the final outcome with vinegar, lime juice and chilli added to taste and see which alternative you prefer.
• Scrape or score the surfaces of the kelp fronds with a small serrated knife, then cut into squares about ½ to ¾ inch wide.
• Place the pieces in a pan and add equal amounts of soy sauce and water so that the seaweed is just covered with liquid. Add the optional flavourings at this point too.
• Bring the contents of the pan to a boil, then reduce to a simmer, cover and cook gently until the seaweed is tender and most of the liquid has evaporated (think of the consistency of lime pickle), adding more warm water from time to time as necessary.
• When done bottle the relish, allow to cool and store in a refrigerator.