Quote:From what I know, if we have x/(2x) food in our city bar the turn before our granary is completed, then it's optimal in terms of food saved (but I don't know why).
Its not correct. We had to have x/(2x) food on turn granary done, not turn before. In this case we'll store X food in granary which will add to food bar after growth.
Optimal food for granary done NOT better then faster granary with nonoptimal food. It just allow you to delay granary 1-2 turn if needed and get the same result.