A method of processing food elements of plant tissue having a cellular structure with substantial starch content comprising arranging the food elements in an aqueous liquid and applying acoustic energy with a selected frequency energy and time profile to modify the cellular structure of a surface portion of the food elements by removing components from the cellular structure and establishing a pectin based surface portion surrounding a core portion and adapted to act as a barrier in a high temperature subsequent cooking process, the modified cellular structure providing for a relatively low moisture surface portion to be established and maintained and moisture to be substantially retained in the core portion after subsequent cooking processes.