Description taken from Arcade version of this game

In Root Beer Tapper, you are a bartender who is so successful that he needs to send his customers away! With your lightning fast skills of tapping a keg and filling a liter mug with root beer, your object is to keep all your customers happy by constantly dishing out root beer to them. Customers range from cowboys to punks to aliens, and they all inch up one of four long-slide bars demanding their share of the frothy liquid. It sounds kind of easy to handle, but you must constantly keep your eyes open. Look out for empty mugs (you dish them out full of root beer while they kindly return them to you) and aggressive root beer-drinkers, because if you thought the life of the bartender was easy...think again. ~ Evan A. Mauser, All Game Guide