A product-carrying unit side portions extending along two opposite regions for engagement with respective support features of a product treatment chamber. A floor region of the unit extends between the side portions and consists of an array of floor region portions with together define a discontinuous upper product-carrying surface of the unit. The surfaces are suitably defined by the upper surfaces of the ribs of the unit. The spaces between the top surfaces of the ribs provide access to the underside of product supported on the discontinuous product supporting surface of the unit and enable heat exchange contact between the heat exchange medium and the underside of the product. The floor region of the unit is shaped to define ducts through which flow of heat exchange medium is directed for contact with the underside of the product supported on the unit.