How do granaries work

[Prospero]

Could anyone explain to me how exactly granaries work ? I know the result is that your city will grow faster, but I never quite understood how. 50 % of food surplus is stored after growth. Does that mean after each turn or after your city has grown one size ? And where is that food stored ? How is it used ?

 

[softflow]

The 50% storage is after growth. Instead of your cities resetting the full growth bar, just after growth with a granary your cities will start with the growth bar 50% full.

Halves the growth time!

 

[Gufnork]

Your city collects surplus food until it has reached a specific number (20 + 1 per population, or is it 2?). Whenever it grows you lose that number and have to start from 0. With granary you get to keep half the food you used to grow, greatly speeding up the growth process.