What does cold shock mean and which mushrooms need it?

A cold shock is a short drop in temperature that signals a colonised block to start fruiting. Shiitake and king oyster respond well to a drop of about 5 to 15°C below their incubation temperature for 12 to 24 hours, sometimes with a cold water soak for shiitake. Many oysters fruit without a shock. It mimics the seasonal cue these species use in nature.