A defrost refrigeration system having a main refrigeration system and comprising a first line extending from a compressing stage to an evaporator stage and adapted to receive refrigerant in high-pressure gas state from the compressing stage. A first pressure reducing device on the first line is provided for reducing a pressure of the refrigerant in the high-pressure gas state to a second low-pressure gas state. Valves are provided for stopping a flow of the refrigerant in a first low-pressure liquid state from a condensing stage to evaporators of the evaporator stage and directing a flow of the refrigerant in the second low-pressure gas state to release heat to defrost the evaporators and thereby changing phase at least partially to a second low-pressure liquid state. A second line is provided for directing the refrigerant having released heat to the compressing stage, the condensing stage or the evaporator stage.