Quoted from Nutmegger:
Would someone with more patience and time than me try this:
1. Develop housing to where it needs (and gets)appetizing food.
2. Once the housing is evolved, reset your market to obtain plain food.
3. See if the housing ever devolves.
Ran into a situation last night where it did not. I know I raised this a month ago, and was told it was probably that the housing just devolved only one level a month, but I'm still not sure. I suspect that the game is only checking that the food is the required level to evolve, and then that there is a continuous supply of food, not that the on-going supply is, in fact, the level required to evolve.
Although I don't see how anyone could have less patience than I, I had a common housing block on a temperate map in the steel age, normal difficulty. There were 46 luxurious apartments (3404 people), fed by one common market square. I changed my desired food quality from appetizing to bland and waited to see devolving housing. And waited. And waited. 5 game years and nothing. Apparently, once the common man has had honey-baked ham, he'll be happy with spam from then on, believing its ham. I decided to check to see if the housing devolved below the levels that required better food than bland whether they would register the difference between bland and appetizing. I removed ceramics, music and one time even water. As long as the house didn't run out of food, it believed spam was ham (bland was appetizing). Curious if the elites were as easily fooled (I had 8 heavenly compounds in a seperate block fed by a grand market), I reduced the required food from tasty to bland. The market buyer eventually got new food, but it must have averaged the food with the existing because it said it had plain quality. The cart pushers started their rounds and the elites were having none of it. Apparently, when you've had pheasant you know spam isn't the same. The food levels dropped and the elite housing devolved. Interestingly, the 5 residents of the modest siheyuan will stay there with no food whatsoever, drinking tea and smashing ceramics. I began to wonder if the fact that the food was the minimum quality the housing required might have some bearing, so I reloaded the map with my heavenly compounds intact and this time lowered the desired quality to appetizing. This time, the elites weren't quite so clever. They accepted the ham as pheasant (appetizing as tasty), and didn't devolve. It seems once they've evolved, you can reduce the common level to bland and elites to appetizing. This might be helpful if you had to import one or more types of food.