Tray for containing food, comprising: - at least one cavity bounded by a lateral peripheral wall and a base, and open at a main opening opposite the base, - a peripheral flange, adjoining the main opening, formed in a sealing plane, and comprising a displaceable outer portion of the peripheral flange and a fixed inner portion of the peripheral flange, - the displaceable outer portion of the peripheral flange and the fixed inner portion of the peripheral flange being formed so as to receive and retain, by attachment, a membrane seal so as to close off the main opening, - the displaceable outer portion of the peripheral flange being formed so as to be able to be moved away from the sealing plane in a first direction for the purpose of opening the tray, in which: - the displaceable outer portion of the peripheral flange is moreover formed so as to be able to be moved away from the sealing plane in a second direction counter to the first direction as far as a folded-down position in which it touches the outer face of the lateral peripheral wall, - retaining means make it possible to selectively secure the displaceable outer portion of the peripheral flange to the outer face of the lateral peripheral wall, - the retaining means comprise flange snap-fitting means and wall snap-fitting means, - the flange snap-fitting means consist of the free edge of the displaceable outer portion of the peripheral flange, - the outer face of the lateral peripheral wall comprises the wall snap-fitting means, which are formed so as to engage with the flange snap-fitting means in order to hold the displaceable outer portion of the peripheral flange in the folded-down position, - the wall snap-fitting means comprise a wall rib projecting on the outer face of the lateral peripheral wall and located at a distance from the peripheral flange, - the wall snap-fitting means are able to retain the flange snap-fitting means in order to snap-fit the displaceable outer portion of the peripheral flange, characterized in that: - the wall rib is oriented with its length parallel to the sealing plane, and - in the folded-down position of the displaceable outer portion of the peripheral flange its free edge engages on the wall rib along its length. - at least one cavity bounded by a lateral peripheral wall and a base, and open at a main opening opposite the base, - a peripheral flange, adjoining the main opening, formed in a sealing plane, and comprising a displaceable outer portion of the peripheral flange and a fixed inner portion of the peripheral flange, - the displaceable outer portion of the peripheral flange and the fixed inner portion of the peripheral flange being formed so as to receive and retain, by attachment, a membrane seal so as to close off the main opening, - the displaceable outer portion of the peripheral flange being formed so as to be able to be moved away from the sealing plane in a first direction for the purpose of opening the tray, - the displaceable outer portion of the peripheral flange is moreover formed so as to be able to be moved away from the sealing plane in a second direction counter to the first direction as far as a folded-down position in which it touches the outer face of the lateral peripheral wall, - retaining means make it possible to selectively secure the displaceable outer portion of the peripheral flange to the outer face of the lateral peripheral wall, - the retaining means comprise flange snap-fitting means and wall snap-fitting means, - the flange snap-fitting means consist of the free edge of the displaceable outer portion of the peripheral flange, - the outer face of the lateral peripheral wall comprises the wall snap-fitting means, which are formed so as to engage with the flange snap-fitting means in order to hold the displaceable outer portion of the peripheral flange in the folded-down position, - the wall snap-fitting means comprise a wall rib projecting on the outer face of the lateral peripheral wall and located at a distance from the peripheral flange, - the wall snap-fitting means are able to retain the flange snap-fitting means in order to snap-fit the displaceable outer portion of the peripheral flange, - the wall rib is oriented with its length parallel to the sealing plane, and - in the folded-down position of the displaceable outer portion of the peripheral flange its free edge engages on the wall rib along its length.