A picked mushroom keeps breathing. DMR's post-harvest bulletin says respiration at 10 degrees is 3.5 times that at 0 degrees, so heat must leave fast. The target is to bring the mushroom itself to 4 to 5 degrees as quickly as possible. The manual asks for button to be chilled at 4 degrees for 6 to 8 hours before it goes to market. Household refrigerators run at 4 to 7 degrees; chill stores at minus 1 to minus 4; freezing below minus 18.
Shelf life without cold is short. Oyster keeps 24 to 48 hours at room temperature and 2 to 4 days in a refrigerator. Milky keeps 3 to 4 days. Button keeps about 12 hours at ambient and 2 to 3 days in a fridge.