Cut the belly of the horse mackerel removing the gill, intestine. Cut the throat of the horse mackerel, carving out along the belly and spine. Be careful not cut along the back.
Divide the head in half, again be careful not to separate the head totally.
Scrape with a knife once it has been sliced open and wash the blood (belly) well with water or thin saltwater. You can use a worn-out toothbrush.
Soak the open horse mackerel in 20% of the saltwater for 20-30 minutes.
Wait until the saltwater stops dripping and dry the fish in sunlight.
A guide to ‘Namaboshi (Fresh Dried)’ is to try pressing with your fingers to get fingerprints. On a cold day (10 ℃ or less in temperature day) morning ~ 3PM is about a good amount of sunlight for ‘Namaboshi (Fresh Dried)’.