"Temperature is like the height or reach of the wall workers - with heat transfer, once two objects are the same temperature, they no longer transfer heat. Similarly, as the wall gets higher, it becomes harder to add bags to it. Eventually the wall will be tall enough that the workers can't reach high enough to add any more bags. If food is uniformly the same temperature as its surroundings, no heat transfer will occur (although chemical reactions will still be occurring, so 'cooking' may still be happening."
An article linking cooking, heat transfer and building a sandbag wall.