I was not sure I would be wild
about the crunchy top, so I did 30 covered / 10 uncovered, and that may have been part of the problem —
less time for
evaporation.
A heavy ceramic cup, doesn't work as good as thermos but works slightly better than
less heavy cup [more a bit more heat capacity and more insulation] But if you don't screw on the lid, a thermos works
about a good as ceramic cup - preventing
evaporation of the hot coffee is large factor.