So I am planning on making and automated drink mixer, I am thinking instead of actuating standard bar optics, I will control the input of the mixers using fluid valves. I have been reading around about this but still cant find a clear answer. What I have seen is that most plastic solenoid valves need an input pressure to work correctly, with a 750ml bottle upside down it will produce around 4 psi at the opening when it is full (I just assumed that most alcoholic beverage densities would be similar to water or less depending on content, not including beer) so as it begins to empty the pressure will drop and most likely cause problems with the valve. My question is are there any valves that require zero inlet pressure ? I do not want to use ball valves with solenoids since the are bulky and expensive. Any advice would be greatly appreciated.
Yes, look for direct-acting solenoids. The ones that need pressure are called "pilot" or "piloted" valves. There are various divisions of Parker that make different valves specialised for different purposes. Once you find the right area, you will find a staggering variety of valves that will solve your problems.
Peristaltic pumps are also a good area to investigate. You get a positive delivery of a specific volume, rather than just opening a valve and hoping that fluid flows.
Everything has to be food-grade as well.
A bottle of around 12" tall will only produce around 0.4psi of head at its outlet so you're out by a factor of 10
Soft silicon tubing and a servo operated pinch wheel will give you ON-OFF function to control free-flow dispensing of fluid. If you want exact measures then, as mentioned, a perilastic pump or similar will be needed.
Anything sold for drinking from (bottles, camel-packs etc) are already food grade so worrying about that aspect of the build is unnecessary. It's amazing how generations have survived before the "health fiends" got involved in food.
"Generations" weren't pumping milk and beer through devices with little tiny crevices that harbor bacteria.
Life expectancy was also significantly less.
Alcoholic drinks have the advantage of killing a lot of pathogens, as do highly sugary liquors.
A rinse-through with schnapps every so often would be an effective and apt bio-control technique!
Gravity feed solenoid valves are near the bottom of this page: Electrically actuated solenoid valves | Cedar Lake Instruments
They need just a fraction of a psi to activate.
I wont be selling any drinks 
this is just a DIY for my personal bar and I think it is a fun project as well. I haven't considered a pump as I assumed it would be expensive but Ill definitely look into it since you do need some sort of volume control other than just timing of a valve. Thank you all I appreciate the help.