The temperature of the compost and the humidity of the room must be carefully controlled in order for the mycelium to develop fully. Eventually, tiny white protrusions form on the mycelium and push up through the peat moss. Farmers call this pinning. The pins continue to grow, becoming the mushroom caps, which are actually the fruit of the plant, just as a tomato is the fruit of a tomato plant. It takes 17 to 25 days to produce mature mushrooms after the peat moss is applied.
Size is no indication of maturity in mushrooms.
Perfectly ripe ones vary from small buttons to large caps. Each crop is harvested over a period of several weeks and then the house is emptied and steam-sterilized before the process begins again. The remaining compost is recycled for potting soil. The harvested mushrooms are set in carts, refrigerated and then packaged and shipped quickly to supermarkets, food processors and restaurants. The entire process from the time the farmer starts preparing the compost until the mushrooms are harvested and shipped to market takes about four months.