A closing device able to be associated with a cooking apparatus of the type where the food product is totally or partly immersed in a cooking liquid, for example a deep fryer, with a main body defining an internal chamber and with a mouth to which a tube to discharge the cooking liquid is coupled. The closing device comprises at least one insert which can be selectively associated with an end open toward the outside of the discharge tube, a closing element which can be selectively associated with the insert, and a gasket interposed between the insert and the closing element.