The granary holds all of the food for your castle. the four food types that are fed to your peasants are meat, bread, cheese and apples. The more food that is available for your peasants, the bigger the popularity bonus will be. For example, for three types of food, the popularity bonus that you get is +9. Whereas when only one food type is available, the popularity bonus is only +4. The maximum popularity bonus you can have from the granary is +15, and this is if all food types are being fed to your population.
You can change which food types are being fed by selecting your granary and clicking on the tick or cross, which will revert it. You can also click on the Apple icon in the popularity menu and this will allow you to see how much food is being eaten every game day, the total amount of stored food as well as the amount produced daily.
The apple orchard is the most basic of food processing buildings in the game. They can however only be placed on grassland and not in the normal environment. The farmer will take the apples to the granary, which helps to maintain the food level.
Hops are used for brewing Ale. The hops farmer creates hops and then takes them to the stockpile. The brewer will then collect the hops and turn them into ale in the brewery. This in turn will increase your overall popularity.
Wheat is used to make bread. This is then used in the granary to increase popularity by feeding multiple food types to your peasants. Note that in order to make bread, you must place a wheat farm, mill and bakery. Wheat farms must also be placed on grassland like all other farms - however, mills and bakeries do not.
Mills take the wheat produced by wheat farms and turn it into flour. This is then transported back to the stockpile for use in the bakery to be turned into bread by the baker. Mills, unlike farms do not have to be placed on grassland, however, you do still have this option.
The baker takes flour from the stockpile and turns it into bread. This is then taken to the granary and used to increase the amount of available food types. The more food types you have, the bigger the popularity bonus given!