Considering that this is Swedish, there should be an entire unit on coffee!
I starting to understand that swedes take their coffee very seriously. Coffee and moose
Since varm can mean both warm and hot, how does one tell what the speaker is trying to say?
I'm curious. Could this sentence mean "the coffee is not hot (but maybe it's still warm)"?
Well, "ljummen" is somewhere between "varm" and "kall".
Edit: The dictionary says that luke-warm means ljummen. What a strange word :)!
Why isn't it "varma"? Is it because "kaffet" and "varmt" are separated by the verb?
It would only be "varma" if the adjective was attributive, so if the adjective was "stuck" between a definite article and a noun.
In a main clause, yes. But not in a sub-clause:
Jag undrar varför kaffet inte är varmt.
The plural form of the adjective, here "varma", is only used when the adjective comes before the noun:
kaffet är varmt - det varma kaffet
hunden är svart - den svarta hunden