A cryogenic food product freezing tunnel including an elongated housing having a food product entrance at one end, a food product exit at the other end, a food product conveyor extending through the tunnel, a cryogen input near the food product exit, an exhaust stack near the food product entrance with an exhaust blower atop the stack, a plurality of cryogen circulating fans spaced along the length of the tunnel, a variable speed directional blower intermediate the cryogen input and the food product entrance, a cryogen input control, and a temperature sensor positioned between the directional blower and the cryogen input. The improved cryogen gas flow control system of the invention comprises a variable speed drive for the exhaust blower and a blower speed control, connected to the temperature sensor, that varies the speeds of both the directional blower and the exhaust blower as functions of the temperature sensed by the temperature sensor; the blower speed control is also a part of the cryogen input control, and varies the cryogen input, again as a function of the sensed temperature.