The ancestor of the modern beer tower was called a
portable keg tap or a
picnic tap, since the device was mostly used at outdoor events, such as picnics. They were significantly larger than modern beer towers. The method involved manually pumping air into the beer container; the resulting pressure within the container would force the beer out the tap. There was also a variant with lager beer barrels that stood upright, allowing
gravity to force the beer out the tap, which is the principle of the modern day system. ==Usage==