This morning I observed something unusual. A common cup
filled up to about 80% with milk, and with about 1/2 spoon of
dissolved coffee, was placed into a microwave oven. I opened
the microwave door at the moment the milk started rising. Then
I removed the cup and placed it on the table. I was glad that
nothing was spilled. Nothing unusual so far.
About ten seconds later I took a spoon (at room temperature)
and immersed it into the cup. That resulted in a sudden rise of
foam with milk and some of my coffee was spilled. How can this
be explained? Why did placing a cold spoon into the hot coffee-
milk produce a sudden boiling-like “explosion?” I have never
seen anything like this.
Ludwik Kowalski