Steps to prepare grain spawn for your mycelium


  1. Soak your grain in hot water. I add just boiling water to a large tub with the grain until the grain is covered by several inches of hot water.
  2. Let the grain sit for 12-24 hours. This helps the grain absorb moisture.
  3. Test the grain by pinching it to see that the grain separates when properly hydrated.
  4. Drain excess moisture from the outside of your grain.
  5. Load the grain into your spawn bags. We recommend the Unicorn Bag sized 3T for your grain spawn. Some prefer to use quart mason jars with a hole in the top of the jar covered with specially prepared lids. When filling your bags or jars, only fill them up to ¾ of the way full.
  6. Place the grain bags or quart jars in your pressure cooker to sterilize based on the method used (bag or jar) and the size of the bag. The recommended pressure is 15 PSI.
  7. Once sterilized in the pressure cooker, you want your spawn grain to cool at room temperature typically for 12+ hours.


Additional Tips:

If you are using the 3T by Unicorn roll down the bag about 2 inches and add about 5 lbs. of grain. Try to keep the top of the bag completely clean of grain and wipe clean as needed. Once full fold over the bag twice.

With larger pressure cookers you can prepare two layers or more of bags stacked loosely to sterilize more spawn bags. We recommend the All American 41 quart for large batches. If you do not yet need larger batches, we have many other sizes available as well.

Answers to the big questions about sterilization

One of the most important parts of your mushroom growing business is sterilization. When you are getting started, sterilization can be confusing. Do you use boiling water, cold pasteurization, pressure cookers (or canners), autoclaves (also referred to as sterilizers). Ultimately, what works for you will depend on your budget, farming set-up, and business needs.

Starting out you may purchase starter pressure cookers that may not get to the higher pressures possible with top end brands like the All American so you will have to run them longer, and you will not be able to sterilize as much spawn grain or substrate with each run. When you scale up your mushroom operation when the demand is there for larger sterilization runs, you will probably want to use a larger reliable brand of pressure cookers. We recommend the All American 941 model.

The All American 941 can hold 19 quart jars or 27 pint jars in each run. It can also hold up to 30 lbs. of substrate in Unicorn bags when stacked properly. The choice of a sterilizer or a pressure cooker often comes down to the cost of the unit. Pressure cookers tends to heat up faster than the electric sterilizers, especially the 110 versions. The 240 versions have more power and do heat up much faster than the 110. A good practice when you are doing runs in either a pressure cooker or the autoclave (sterilizer) is to reload the unit for the next run while it is still warm from the previous run. In order to do so, you will need tongs, or good gloves to deal with the heat on jars or sterilized bags.

Do not forget if you are working with grain spawn you can also use the smaller Unicorn Bags instead of the mason jars. This allows you to create much larger batches as you grow and scale your farm.