How to easily build a simple DIY steaming vessel for mushroom substrate sterilization:
The first thing to do is find a suitable containing vessel for your mushroom steamer. I used a 5000L tank, that was used previously for storing fuel. This vessel was cut in half and cleaned out. At our local blacksmith, I had a basket manufactured that could hold about 120 bags of mushroom substrate (see pictures below). This basket fits inside the steaming vessel with enough space around the edges for steam ventilation.
Use a high pressure gas burner and propane gas for heating the water (other ways can be used to heat the water, including wood fire and electricity.) It will take about 12kg of gas to successfully sterilize 120 substrate bags for 5 – 6 hours. Use enough water under the basket to last the 6 hours of steaming. If the water runs out, the dry heat will damage your substrate bags.
Cover the steamer to maintain constant temperature and steam flow. Some steam will naturally escape. I use three blankets and a tarpaulan to cover my steamer and then tie the covering tightly around the edge of the steamer.