Abstract: A cap includes a plunger member including a cavity portion integral therewith and extending downwardly therefrom. The cavity portion is capable of containing additive therein and includes a lower portion having an opening for dispensing the additive into the container. A receiving member receives the plunger member and includes a threaded portion for engaging a container. A spring member is preferably disposed between the cavity portion and a neck portion and becomes compressed when the plunger member is moved towards a down position. A membrane preferably extends across an opening of a container and engages the opening of the cavity portion when the plunger member is at an up position. The membrane may be formed from aluminum foil so that it can be penetrated when the plunger member is moved to a down position and to thereby allow the opening of the cavity to pass therebelow so that the additive can be introduced into a container.