A simple method that sorts potatoes based on their specific gravity—an estimate of their solids content—can be used to find potatoes that are ideal for frying. Prepare two tubs of brine: the first should be nine percent salt relative to the weight of the water (8.25% salinity) and the other twelve percent salt relative to the weight of the water (10.7% salinity). Plunge each potato into the nine percent brine first; potatoes that aren't too wet should sink in this brine. Then drop these potatoes into the twelve percent brine; potatoes that aren't too dry should float in this brine.