A system and method for dispensing a predetermined portion of a beverage or drink additive using a cost effective portion control valve that replaces electrical components with mechanical components. The present invention dispenses a controlled portion of a beverage when a lever is activated. A magnetically coupled linkage system can control the exact amount of fluid dispensed. A valve block contains a beverage input, a beverage outlet, and a valve seal. A lever arm is connected to the valve seal and connected to a magnetic housing containing a valve magnet. A yoke pivots about the valve block where the yoke contains a yoke magnet aligned to interface with the valve magnet. A lever arm return spring is connected to the lever arm and the valve block to bias the lever arm return spring to a resting position. As the yoke pivots beyond a predetermined distance, the yoke magnet separates from the valve magnet allowing the lever arm to return to the resting position closing the valve.