I believe the foam on your instant Coffee has a lot to do with your water supply and how you boil it. For example if you take std tap water unfiltered place a tea bag in it and then microwave it until it starts to boil you will get lots of strange foam.
Water treated with a reverse osmosis filtration system stops the foam being produced.
A microwave is not a good way to make tea or coffee but you get scum appearing on tea or coffee if the water is not filtered no matter how you heat the water..
