Microwave makes my tea/coffee foam - why?

So, Idiot Co-worker comes into the kitchen, finds a full kettle of boiling water. Dumps the freshly boiled water down the drain because “He doesn’t know how long it’s been sitting there and doesn’t want lead poisoning.” :smack: This is par for the course in this office.

Since my department has the heaviest workload in the office and I really just can’t stand over and guard the kettle for the “only 8 minutes to boil!” (I really can’t), I’ve given up and I stick a mug of water in the microwave.

I’ve noticed, when I take my hot mug of microwaved water back to my desk and thrown in either a tea bag or instant coffee, it’s foamy. This doesn’t happen on the rarest occasions when I actually get the water I boiled in the kettle. What is happening?

This is asked often in these forums, but nothing appears in a board search for me today. I got this link using google search.

The key word is nucleation.

Ah, thanks.