"Mead is delicious!"
Translation:Sima on herkullista!
I think it's about countability. Sima would become partitive when not in the subject position (due to the uncountability of liquid), so its adjective will be partitive in this sentence. I've tried to demonstrate this but the sentences may contain errors:
Onko teillä simaa?
Joo, meidän sima on herkullista.
Onko tuo suklaakakku?
Joo, tämä kakku on herkullinen.
I'm trying to think of a sentence where I would say that, but I come up with none. "Tämä sima on herkullista." "Lasi on kaunis ja sima on herkullista." "Rusinat ovat maukkaita (The raisins are tasty) ja itse sima on herkullista." "Sima tässä on herkullista." "He sanovat, että sima on herkullista." "En arvannut siman olevan näin herkullista." (I didn't expect the sima to be so tasty) etc.
Maybe if "a sima" was some sort of an edible thing like a meatball or a cake in some other language and we told that that specific piece of food is delicious, then we would say "Tämä/tuo sima on herkullinen" but no other scenario would fit.