Wheat Straw For Oyster Mushrooms
One of the best substrates to fruit oyster mushrooms is wheat straw. It is readily available and cheap. The hobbyist can buy straw directly from the farm or farmer’s market or any large animal feed store.
Mycelium grows very quickly on straw; usually within two weeks, the wheat straw bag is fully colonized and ready to fruit. The straw should ideally be chopped into smaller pieces. This will allow the mycelium to take over the substrate faster. Chopping is done by putting straw in a clean barrel and using a clean weedeater.
There are mainly two methods of pasteurizing straw. The first is heat pasteurization and the second is hydrated lime. The heat method is basically putting straw in hot water between 70-82C (158-180F) and letting is sit for at least one hour. This makes the straw flexible and hydrated while the heat kills off possible contaminants, giving the mycelium a head start to colonize the straw. Pasteurization is not the same as sterilization- just something to keep in mind. We do not sterilize straw; we pasteurize.
Lime pasteurization works by using chemicals. The idea is to put the straw in water and add as much hydrated lime as needed to bring the PH of the water as high as possible, usually near PH of 13. Such a violent change in the PH kills contaminants. Ideally, the hobbyist should let the straw sit in hydrated lime water overnight. Caution when using hydrated lime, as it can damage skin and lungs since it is a chemical.
There are many types of hydrated lime, but the one used to pasturize straw must have a very small amount of magnesium, ideally < 1%; anything higher and it may negatively impact the growth of mycelium.
Both methods of pasteurization work well and are matter of personal preference, as well as what we have on hand.
Pasteurization can be done indoors or outdoors. Hobbyist can use the pan of a the pressure cooker and fill it up with straw. Pour hot water until the straw is submerged, and put something heavy on top to force the straw to go under the hot water. Closing the top of the pressure cooker will help keep the heat in.
It is also possible to pasteurize in larger quantities using barrels outdoors. Metal barrel works best for heat pasteurization, and plastic barrel works best for hydrated lime pasteurization.
Once the straw is pasteurized with heat or with hydrated lime, it is taken out of the container to allow it to cool down and lose excess water. In the case of hydrated lime pasteurization, it is important to allow the straw to sit for few hours, ideally overnight, so that the PH levels of the straw return to normal before inoculation.
With the straw ready, the hobbyist can mix straw and grain spawn, and then create bags. Straw bags need to be compact for the straw to touch each other. If there is too much space between the straw, the mycelium will have a difficult time colonizing, so it is important to push on the straw and create a very compact bag in order for the mycelium to travel easily on the substrate.
All that’s left now is to close the bag and make a few holes in the bag to allow for air exchange. The larger the bag, the more holes we can make. In two weeks once mycelium has colonized the bag, it will be time to move the bag over to the fruiting chamber. It is through these same holes, that pins will come out and grow to become mushrooms.
Please see our other blogs covering more specific subjects about the fun world of growing mushrooms.