A plasma generating apparatus comprises a first, powered electrode and a second electrode structure located in front of the first electrode. An insulating layer is interposed between the first electrode and the second electrode structure. The second electrode structure has a plurality of second electrode portions defining gap portions therebetween. The width of the gap portions is w. The second electrode portions each have a forward surface and the gap portions each having a forward surface, the height difference between the forward surface of each second electrode portion and the forward surfaces of the adjacent gap portions being h, and wherein h is at most 1 mm and the ratio w/h is at least 1. Thus, the forward surfaces of the second electrode portions and the forward surfaces of the gap portions together provide a smooth topography. The plasma generated by the apparatus (in air or other oxygen-containing gas) forms ozone, which can be used to treat foodstuffs, for example. The smooth topography allows substantially all of the plasma to be generated inside a package whose wall is pressed towards the second electrode structure.
