A method for aerating a pasty product and for mixing with another product is disclosed herein. In one example, the method includes passing a stream of pasty product to be aerated through an apparatus. The apparatus includes a housing, the housing including an inlet for the pasty product to be aerated an outlet for the aerated product. The apparatus further includes a gas injector for injecting a gas into the pasty product to be aerated. The apparatus further includes an intermediate mixing chamber and a secondary product introduction member. The method further includes injecting via the upstream gas injector a gas into the pasty product stream at a position upstream relative to the first set of a rotor and a stator. The method further includes injecting a secondary product via the secondary product introduction member into the intermediate mixing chamber.