Arno posted one of his secrets to keep the masses happy.
He produces grain wherever possible. In cities where grain is only produced inefficiently, he ensures that the production is slightly higher than consumption and he has set the minimum sale price to 1GS. Apparently the price settles at 35GS. While he is subsidizing heavily, the expense is worth the effort. First, he saves on tonnage to haul needed grain to the location. Secondly he saves storage costs, since there is no need to keep a supply that lasts until the arrival off the next convoy.
I assume from further communications that he does likewise for other bale goods, such as fish, wool, hemp etc.