The present invention refers to a method of preparation and packaging of a fresh food product with respiratory capacity for its conservation and later steam cooking in a microwave oven characterised in that the method comprises washing of the food product injecting ozone in the washing water, introduction of the washed food product in a container, thermosealing of the container containing the product with a transparent material provided with one or more vents for the escape of the steam, and later application of a vacuum with the aim of conditioning the container