Abstract: A method is provided for the two-stage pressurizing of a product in which a propellant gas may be immediately generated for use as a high-pressure propellant after the sealing of the container. A first reactant and the flowable or sprayable product which is desired to be dispensed is placed into the container until the container is substantially full. The container is then sealed. A second reactant, which may be dissolved in a further amount of product, is introduced in liquid form into the sealed container through a dispensing valve, another valve, or a sealable plug. The first and second reactants react to generate the propellant, which is then contained or dissolved with the product in the container until needed. As product is expelled, the propellant evolves out of the product to exert expulsive pressure. Thus, the invention involves the process of charging during the filling of product and allows the product to be dispensed promptly and continuously thereafter.