The process according to the invention for defrosting frozen or deep-frozen foods comprises the following steps: S1.1) providing a portion of frozen or deep frozen food (7); S1.2) bringing the portion of food to be treated (7) into contact with a treatment liquid (5); S.1.3) transmitting, through the treatment liquid (5) ultrasounds to the food to be treated (7) in order to diffuse the ultrasounds into the food to be treated (7). It allows defrosting foods faster and better preserving the organoleptic qualities thereof. The invention also relates to an apparatus and a computer program for executing said process. The apparatus may comprise a treatment container (3) the inner walls thereof are covered with a layer of ice.