PCT/SE Application 93/00204 discloses a hot air oven for the preparation of foodstuffs wherein deep-cooled foodstuffs such as, for example, chipped potatoes, can be introduced in a wire basket into a refining chamber in which they are at first refined in hot air without air exchange. In this phase the refining chamber is closed, so that the moisture escaping from the foodstuff ensures a hot steam atmosphere in the refining chamber. When the foodstuff has been completely refined, an air supply channel and an air discharge channel are opened via slides, so that the moist atmosphere can escape from the refining chamber and a dry, hot atmosphere regenerated instead. In this phase, also known as the roasting phase, the foodstuff acquires the browning necessary for the vision and the senses.
It has been found in practice with the prior art hot air ovens that it is a problem to open and close the air supply and air discharge channels by means of slides, since the slides must be cleaned relatively frequently, as they tend to become sticky due to the grease-containing atmosphere in the refining chamber.