A heating medium injector includes an injector structure defining a heating medium flow path and a product flow path. The heating medium flow path extends to a contact location along an axis of the injector, while the product flow path also extends to the contact location along the injector axis. The contact location comprises a location at which the heating medium flow path and product flow path merge within the injector. In a region along the injector axis, the product flow path is defined between a first flow surface and a second flow surface. The first flow surface comprises a surface of a boundary wall separating the heating medium flow path from the product flow path and the second flow surface comprises a surface of an opposing second boundary wall. The second flow surface is in substantial thermal communication with a second flow surface cooling structure.