A method of pasteurising and vacuum packing food (2), comprising the steps of placing the food (2) on a tray 81) having a flexible bottom (7) and stiff lateral walls (8) extending in the vertical direction of the tray (1), up to a filling degree of 410-60% of the maximum volume of the tray (1), covering the tray (1) with a flexible cover layer (3) to form a package, providing a one-way valve (4) for one-directional communication from the interior of the package (5) to the exterior thereof, pasteurising the contents inside the package (5) thus formed by means of microwaves, closing the valve (4) upon completed pasteurisation of the package and cooling the package (5), whereby a vacuum is created in the package (5) in such a manner that the package (5) with the vacuum-packaged food (2) therein presents a centre portion where the distance between said flexible cover layer (3) and said bottom (7) is shorter than the distance between said flexible cover layer (3) and said bottom (7) at the peripheral edges of the package.