What makes these tiny droplets of coffee"levitate"?

I have observed tiny droplets of coffee floating frictionlessly above the surface of my coffee. They are created when a styrofoam or paper cup is pulled slowly across a table. The vibration of this action seems to create the droplets. They last a few seconds and quickly skim around on the surface, shrinking and finally vanishing.

These are NOT air bubbles, I can clearly see an amount of refraction in them which would not occur through the thin film of a bubble.

My thought is that as they are created, a small electric charge is placed on them, repelling them slightly above the surface...

Any more ideas?

Thanks!