This is a process to make a shelf-stable, liquid, ready-to-drink, aseptic nutritional formula for the treatment of PKU, tyrosinemia or other errors of metabolism. The liquid nutritional formula has caseino-glyco-macropeptide as the primary protein source and complementary essential amino acids to complete the requirement profile. The beverage also includes vitamins and minerals sufficient to meet daily requirements. When used as a complete diet, the nutritional formula includes a carbohydrate source and a fat source. The nutritional formula has a pleasant taste.