Is that mold? Or a reaction between 1 tablet of sweetener and the remaining bit (about 10 drops) of coffee + 1.5% cow's milk?
I had already thrown the sweetener into the cup and forgot to add the coffee straight away… about 30 minutes later it looked like this. It happened to me several times with the same result. Google can't find anything about it.
In both cases (mold/reaction) please give an explanation. Thanks
by TheStroboCop