How would you measure the amount of air that gets whipped into a liquid when you stir it?

Bear with me here. The paper cups you get at a takeout coffee shop have a ridge going down the side where the cup is glued together. Depending on which way you twirl the cup to stir your coffee to cool it off, the coffee will either go with or against that little ridge. I initially wondered how much more air than tiny, hair thin ridge would whip into a cup, but now I am more wondering how you would even measure that in a lab