Final Idea

I think this is the idea I'm going to go with. There will be four bottles each with a different coloured liquid in it and a different smell inside the cap. I'm thinking of also having a pattern on the outside of the bottle.
Each bottle will have the same flavour liquid in it though. And the user will be asked to line them up from favourite to least favourite.
I have gone with spray bottles after a test that I conducted showed that people would be uncomfortable with cups or drink bottles.