An endless conveyor belt (1) of a belt conveyor system in a plant for air treatment of food products follows a helical path section (2) preceded by a straight path section (3) and followed by another straight path (4) section. In the preceding straight path section (3), the conveyor belt (1) remains collapsed and in the following straight path section (4), the conveyor belt (1) remains expanded. At the transition between the preceding straight path section (3) and the helical path section (2), the conveyor belt (1) is expanded along the outer lateral edge of the belt. At the transition between the helical path section (2) and the following straight path section (4), the conveyor belt (1) is expanded along the inner lateral edge of the belt.