solenoid
Drinks are corrossive substances and can react with ordinary materials( eg., you can etch a PCB in coke, given enough time!)
Electromagnetics are simple enough, as far as they are industrial and not 'Food Grade'.
The 'pinch cock' method is tricky, not to mention wasted current consumption: it has to overcome the liquid inertia as well as the pipe/tube elasticity. Solenoids ARE power hungry!
The simple and probably cheap solenoids come out of Water Filter-dispencers, Coffe/soft drink vending machines, and are designed for liquids under pressure, temperature and chemical extremes.
Alternative to this and for experimentation, you can dismantle DC or AC relays rated at at least 20A contact current capacity, and use the coil. You have to use soft iron for better performance. ( nails are Mild steel) and retain some permanent magnetism ). The Relay coil will be found sitting around one of these soft iron cores. AC single /#phase contactors are the best bet. having awesome pulling power.
For the valve mechanism, a steel ball (Teflon coated) freely seated on a rubber O ring by gravity inside a vertical Corning glass/ nonmagnetic chrome steel tube would be an ideal construction. The relay coil will surround this tube such that the ball will be lifted up due to the magnetic force field.
stevez' second option is fairly easy, and i feel the best method. CO2 gas or even an electric Tyre inflator, at low pressuere can be used to eject the fluid through a siphon tube. You neednt concern yourself about 'food grade, acid resistant materials' at all!
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