Abstract: A method for packaging a product in a hermetically sealed container having a cup-shaped rigid or semi-rigid body with a rim fitted with a closure, the method comprising introducing the product into the cup-like shaped body. Forming an isolated space with a gas inlet and a gas outlet, the space defined between the body and a closure-forming member adjacent to and with a clearance from the rim. Introducing a replacement gas through the inlet to replace at least a substantial portion of gas originally contained in the isolated space, and displacing at least one of the body or the closure-forming member towards the other of the two members to close the clearance and to attach the closure-forming member to the rim, and hermetically attaching the two to one another to form a gas-tight steel.