The current document is directed to methods and systems for manufacturing frozen-sushi food products that remain texturally and compositionally stable while frozen and refrigerated for extended periods of time. A variety of different processing steps and ingredients are employed to prevent retrogradation of gelatinized starch in cooked sushi rice, including quick cooking of the rice, employing non-nutritive sweeteners in place of sugar, controlling the amount of salt in the sushi rice, and use of β amylase and gellan gum.