By having it open to the air you get a lot more of the aroma of the drink which is a bit part of how we experience taste. Mostly it's just a neat trick to demon

By having it open to the air you get a lot more of the aroma of the drink which is a bit part of how we experience taste. Mostly it's just a neat trick to demonstrate zero-/micro-G fluid handling and dynamics packed into a relatable form. Principals like this are used in fuel/liquid handling in space already to make sure your tanks aren't pure chaos and your pumps don't run dry. A lot of rockets just do ullage burns with different motors to settle their fuel into the bottom of tanks but that's not possible for all fluids if you need to have them moving continuously or can't do burns just to settle them.