The present invention relates to an oven comprising: ⋅—a first and a second chamber and one heater per chamber to heat a gas which cooks a product, ⋅—at least one gas circulation means, which establishes a gas circulation in one chamber, ⋅—endless conveyor means for transporting products from an inlet through the chambers to the outlet, wherein the conveyor means are at least partially arranged in a helical path, ⋅—separation means to separate the first and second chamber, wherein the conveyor means pass through the separation means, ⋅—natural smoke gaseous supply which supplies gaseous smoke to at least one of the chambers, wherein the smoke supply is provided upstream from the circulation means.