A system for grinding food, comprising: - a machine for grinding food comprising a section for loading the food to be ground and a discharge duct for the ground food; the said discharge duct having an axis thereof that extends longitudinally and an outlet for the ground food; - a kit of interchangeable perforated plates which comprises at least a first type of perforated plate having a first type of perforation and a second type of perforated plate, having a second type of perforation, said outlet being closable by each of said perforated plates; and - a safety kit comprising at least two mutually different interchangeable elements of which a first interchangeable element is compatible both with the perforated plates of the first type and with the perforated plates of the second type, and has an integrated protection body that is adapted to prevent cutting accidents from happening to the operator, while the second interchangeable element is compatible exclusively with the perforated plates of the second type and lacks said protection body; locking means being provided for keeping said perforated plate fixed on said outlet; said locking means comprising at least one axial coupling for locking said perforated plate in rotation, and an annular cap that is facing toward the said perforated plate and fixed on said outlet in order to retain said perforated plate in the direction of said axis; wherein said axial coupling is defined by at least two parts, of which a first part is arranged on the said outlet of said discharge duct and a second part is arranged on an interchangeable element being part of said safety kit interposed between said perforated plate and said annular cap. - a machine for grinding food comprising a section for loading the food to be ground and a discharge duct for the ground food; the said discharge duct having an axis thereof that extends longitudinally and an outlet for the ground food; - a kit of interchangeable perforated plates which comprises at least a first type of perforated plate having a first type of perforation and a second type of perforated plate, having a second type of perforation, said outlet being closable by each of said perforated plates; and - a safety kit comprising at least two mutually different interchangeable elements of which a first interchangeable element is compatible both with the perforated plates of the first type and with the perforated plates of the second type, and has an integrated protection body that is adapted to prevent cutting accidents from happening to the operator, while the second interchangeable element is compatible exclusively with the perforated plates of the second type and lacks said protection body; locking means being provided for keeping said perforated plate fixed on said outlet; said locking means comprising at least one axial coupling for locking said perforated plate in rotation, and an annular cap that is facing toward the said perforated plate and fixed on said outlet in order to retain said perforated plate in the direction of said axis; wherein said axial coupling is defined by at least two parts, of which a first part is arranged on the said outlet of said discharge duct and a second part is arranged on an interchangeable element being part of said safety kit interposed between said perforated plate and said annular cap.