I remember reading somewhere about a magic jar that produced an inexhaustible supply of spices that magically made anything cooked with them taste fantastic. It didn't change the mechanical effects of eating the food: poisons would still be poisonous, magic food would still have its effect, rations would still work normally, they'd all just taste better. I think the book it was in was for 3.5, but references from either 3.0, 3.5, or Pathfinder will work. I don't even much care if its the same item I read about before, so long as the functionality and fluff are fairly close.
The Spice Jar from the Ferun setting is close to what you describe. It does however provide some bonuses aside from good tasting food.
A Pathfinder solution could easily be created using Wonderous Items rules. With DM approval any item can be created.
This item would likely be a continuous prestidigitation effect. Which by the magic item GP value estimation chart means it would cost Spell Level (prestidigitation is level 0 so this would be ½) × Caster Level (1) × 2000 which would make this item cost a low 1000 gold.
I used Prestidigitation because one of the abilities it has is:
It can chill, warm, or flavor 1 pound of nonliving material
The item could easily be fluffed as producing a powder that flavors food to perfection.