Most fountains don’t trust the operator to mix the citric acid and corn syrup as two separate streams from the other ingredients. (At least they didn’t at the time. The big computerized ones might do that these days; but those are probably self calibrating.)
This is how all fountain drinks work. Concentrate, water and pressurized CO2 canisters.
> Coke brand milk.
Well, it’s a drink company...
> Coke brand grade D but edible meat
Hard nope from me. At any grade.