a cryogenic freezer apparatus for food products includes a conveyor within a thermally insulated enclosure . a cryogen injecting unit is located in said enclosure adjacent the opening thereof , and responsive to a cryogen control signal for introducing liquid cryogen in said enclosure . a blower unit in said enclosure directs cryogen vapor away from said enclosure opening toward the interior of said enclosure . the output of said blower unit being controllable by a blower control signal . a sensing unit within said enclosure senses the cooling capacity of the cryogen vapor at the enclosure opening and generates a sensor output signal which is indicative of the amount of cryogen vapor escaping out of said opening . a control unit , coupled to said sensing unit , said injecting unit , and to said blower unit generates a cryogen control signal and a blower control signal in response to the sensor output signal . cryogen vapor escaping from the enclosure is limited to an amount needed to maintain an air lock , thus preventing air intrusion into the enclosure .