Process for growing mycelium sheets. First, a substrate mixture is prepared in a mixer. Then the substrate mixture is applied as substrate layers on shelves of a rack in a cultivation room. The cultivation room is then closed and subsequently the substrate is pasteurized by injecting a pasteurizing medium, such as steam, into the closed cultivation room. In a next step, the substrate mixture is cooled and subsequently inoculated. During a growing step mycelium is allowed to grow on the inoculated substrate mixture. In a next harvesting step, the mycelium is separated from the substrate.