This invention relates to a flexible bag for storing raw milk where the flexible bag is for use in system comprising a cassette adapted to contain the flexible bag, where the flexible bag further comprises a spout, preferably with a screw top, and two or more perforations for fixing the flexible bag inside the cassette when the former is mounted in the cassette. Additionally, the invention relates to a cassette for use in a system comprising said cassette and the flexible bag, where the cassette comprises at least two sets of small pins, and at least two sets of cavities, where said cavities are adapted to receive said pins, and wherein said pins are constructed and placed such that they penetrate said perforations of said flexible bag, when said bag is placed inside said cassette. The invention also relates to a system comprising a cassette, a flexible bag and a heating tub adapted for holding a heating liquid, such as water, where the heating tub comprises a rack module for holding the cassette such that it is at least partly covered with said heating liquid.
