A substrate cake is a form fitted block of substrate intended to be colonized by mushroom mycelium. Most commonly, a cake is made of brown rice flour and vermiculite as in the famous PF Tek, but a cake can be constructed of any material that mycelium can colonize and hold together.
Fruiting a colonized cake
The most common way to fruit a cake is to remove it from the jar or glass in which it colonized, into a humid environment from which it can bear fruit bodies.
Colonized substrate cakes are often dunked before they are moved to a fruiting chamber and between each flush to increase hydration within the cake.