In the case were someone/something is a recipient you use "para". I think of it as a "gift". Some have said "por" in this case would mean "in exchange for". You would be trading food for the judges if you use "por" here. Though both ideas might use the same English.
This is becuase "es" applies to the food which is singular.
In case you say "The judges are for the food." you should use "son" instead of "es":
"Los jueces son para la comida." as "son" applies to the judges which are plural.