Gather some of the fruit (Achiote, Bixa orellana) and scrape out the seeds into a bowl using a spoon. Add some water and allow to soak for a few hours or overnight if you have time.
After soaking, strain the water in a separate bowl. Add a little water to the seeds and rub the seeds between your hands to get some more of the dye out and strain again. This could be done about three times.
Bring the roucou to a boil and add salt to taste. Not too much though. Set aside to cool. When cool pour in bottles and store.