Note: Food rot is now in testing, you should get messages about how much food would have rotted, please report here if the values seem ok to you. They should be a bit higher than rot in the granary for the same amount and time. They may seem high because they are accumulated, i.e. in the granary you see a few bushels rotting away every day, on expired market offers you'll get the entire rot for a week or whatever in one large deduction.