Before making the marinade, measure how much you will need to completely cover the salmon. Then dissolve 10% (by water weight) of salt and 5% (by water weight) of sugar in water.
Tip: dissolve salt and sugar in half of the amount of hot water, replace the other part of the water with ice. This way the salt and sugar will dissolve faster and better.
Dip the salmon in the marinade and leave in the refrigerator.
The shortest marinating time is one hour, but you will achieve a much better result if the salmon is soaked for at least 4 hours. We sometimes leave it in the fridge overnight and nothing bad happens.
The next important step is to take the salmon out of the water, drain it, sprinkle it with olive oil and keep it covered with cling film in the fridge for a few hours before eating.