Translation: R. Sørensen
The word "rak" comes from the word "rakr" in the Norse language, meaning moist or soaked (Falk and Torp: "Etymologisk ordbok over det norske og det danske sprog", 1906). The word descends from Indo-European "req", which mean source or drop, and which is also related to the word rain. We can also find the word in irrigation. The rakfisk is put into a tub and then fluids are formed, it is brined. In the oldest sources, on the other hand, the rakfisk is mentioned as "brine- cured fish". And of course, originally the fish was buried or put in underground cellars. The supposition for this conservation method is an even soil temperature at about 4 degrees Celsius, and that's why the tradition is found around the polar circle at the northern hemisphere. We know of raking of salmon, herring and shark in addition to the gwyniad and trout/char that are the most commonly used today.
You use some trout (mountain trout or char is the best), though farmed trout will also do. They should be about 750 g big.
Scrub the fish so that all the slime is gone, remove gills and guts and rinse well so that all the blood is gone. Scrub the blood stripe with a fish brush. Rinse the fish and put it in vinegar solution for about half an hour. Let the fish rest and the vinegar run of for a while.
Put the fish in a tub with strait sides. Close side by side with the abdomen up. The abdomen is filled with ocean salt, 60g per kg fish. Some sprinkle tiny amounts of sugar to speed up the raking, but not more than a pinch for each layer of fish.
Then the fish is put under pressure with a lid that fit down into
the tub and a rock, and placed chilly. A stable temperature at about 4 degrees
Celsius is the best, but it should at least be below 8. After a couple of days
you should check if the fish is brined. If it is not enough fluids to completely
cover the fish, add salt brine containing 40g salt per litre of water. Some
place the fish at a higher temperature for some days to make it brine better,
but that should one be very careful with.
Leave the rakfisk for two to three months. Rakfisk is well conserved in the brine. When the fish is appropriately rak, you can put it into a new 4 percent salt brine, which will slow down the rake process. An other method for slowing it down is to put the tub in the freezer - or outside if you live in a place in the world where it is stably cold for some time of the year. As long as the fish lay in the brine it will not freeze. Otherwise the rakfisk is not good for freezing.
Grünerløkka rakfisklag homepage (Norwegian)