Coffee is the one thing that makes me bearable before noon, so when there is something weird going on in my cup of coffee, I notice it.
Kathy noticed something weird going on with her coffee and sent me this coffee question:
“Hey Ray! In the morning, I pour cold brew into my mug, microwave it for two minutes, then add cream and sugar. When I stir it, I get a concert! Can you explain?”
Along with that question, she sent in a video of the clanking noise of her spoon hitting the cup, lowering in pitch with every stir!
Ray Petelin 
This coffee concert with a dropping octave is more common in hot chocolate and goes by the name “The Hot Chocolate Effect.”
When the powder is dissolved in the hot water, the sound pitch drops.
Getty Images 
A paper in the American Journal of Physics states that if a large cylinder of water is filled with hot tap water containing dissolved air, the pitch may descend by nearly three octaves during the first few seconds as air comes out of the solution. This means air is to blame for the lowering pitch!
Getty Images 
Remember, Kathy said she warms up cold brew coffee.
Cold liquids can dissolve gases, like air, more easily than warm liquids. This means when Kathy introduces the room temperature sugar and cold cream, she is introducing something with dissolved air in it.
That air lowers the pitch of her coffee until it is released from the solution.
