because the metal press can turn a single cloche growth cycle of melons into 9 slices aka 9*80ml=720ml of ethanol
compare that to the hemp seeds that produce 2 seeds per cycle, aka 2*120ml=240ml of plantoil, this would mean that the probably meant to be very efficient rate of hemp would be eclipsed by a factor of 3. As in, you need 3 hemp cloches per melon cloche.
The next best ethanol source from cloches would be potatoes with 2*80ml=160ml per cycle
Even if melon slices would be reduced to 20ml per slice, they'd still give 180ml and remain the best,. though not by much. Could use the extra 20ml to reward players for building a thing with a metal press in it's loop, but I don't know how well it is "lorewise" "feelwise" to have melons as the best source of alcohol. Welp. Enjoy figuring that stuff out :D