Abstract: Apparatus for blast freezing palletized products is disclosed in which tall racks have openings on at least one side that connect to a plenum chamber, against which stacked pallets can be placed one above another as well as beside one another adjacent the plenum openings, but with the rack providing only one pallet depth to optimize circulation of regular warehouse freezing air through the pallets at a rapid rate for rapid blast freezing. As another example, there are vertically adjustable panels in a tall rack to accommodate different height palletized products stacked one above another, in a way that allows for sealing between the plenum chamber and the palletized products on one side of the palletized product without either substantial blockage of air flow through the side of the palletized product and without allowing a substantial gap between the palletized product and the plenum that would allow a substantial bypass of flow through the palletized product.