Sterilizing Rye Grain for Spawn in an Instant Pot

Ingredients:

Instant Pot

Mason jars with filtered lids and rings (I prefer the “1 pint” wide mouth jars)

Rye grain 

Mixing spoon or paddle 

Colander, muslin bags or cheese cloth 

Aluminum foil (optional)

Gram scale or measuring cups and spoons (optional)

Gypsum powder or gypsum pellets (optional)

Aluminum foil

Directions:

 

 

Procedure

Principle

1.

Measure the desired amount of grain. 

Conversions: 

 

90 g dry grain per pint jar

 

½ U.S. cup dry grain = 90 g

 

As a general rule of thumb, rye grain will double in volume and mass after the soak and boil. 

 

One way to estimate the amount of grain is to fill the intended spawn jars approximately ¼ to ⅓ full with dry grain. 

 

2.

Add the grains to the instant pot. Fill with water until there is at least 1 inch (~2.5 cm) of water above the grain. 

 

Some of this water will be absorbed, it isn’t going to hurt to have more than an inch above the grain. 

3.

(Optional) Add 2% (by weight of dry grain) gypsum powder or pellets to the bucket and mix. 

 

 

 

 

 

 

 

Conversion:

 

1 teaspoon of gypsum powder weighs about 3.4 g.

 

1 teaspoon of gypsum pellets weighs about 6 g. 

 

Gypsum powder helps establish a more basic pH of the grain spawn, adds several nutrients to the grain, and helps prevent grains from sticking to each other. 

 

4.

Install the lid on the instant pot and allow the grains to soak for 12-24 hours. 

 

Soaking allows the shell of the grain to soften and absorb more water later, when boiling.  Soaking also provides the perfect environment for mesophilic bacteria to thrive and blossom, only to be subsequently killed off during the boil. 

 

5.

Remove the lid from the instant pot.  Add more water if necessary to raise the water level at least 1 inch (~2.5 cm) above the top of the grain.

 

Changing out the water will wash off the gypsum powder and affect pH. 

 

The grain will have absorbed water during the soak.  More water may be necessary to prevent the grain from drying out during the boiling step.

 

6.

Bring the grain to a boil: 

  1. Ensure the lid is removed from the instant pot.
  2. Press the “Saute” button.
  3. Press the “+” button until the cook time displays about 30 minutes. You will not be boiling for 30 minutes, but this setting the burner doesn’t turn off prematurely.
  4. Allow the instant pot to turn on.
  5. Stir the grain several times as the temperature rises. This helps prevent the grain from sticking and scorching on the bottom of the pot.
  6. Allow the grain to boil for about 5 minutes, then press the “Cancel” button.
  7. Allow the grain to steep (sit without stirring) for about 5 minutes.
Boiling helps the grains absorb water, and starts the process of killing off some contamination prior to drying and sterilization. 
7. Drain the grains into the colander and shake to drain. If you don’t have a colander, pour grains into a muslin bag or cheese cloth and hang to drain.  Allow the grain to drain for approximately 15 minutes.  Stops the soaking process and prevents grain from expanding and breaking. 
8. Spread the grain out on a pan or solid surface and allow it to air dry for about an hour.  Grains are ready when just dry on the outside.  While the grains are dry on the outside, the insides have absorbed the perfect amount of water to support mycelium colonization later on. 

 

Grains that are not allowed to dry enough during this step may be susceptible to wet rot during the colonization phase.  

Grains that are allowed to dry too much may not have enough moisture content to support the healthy growth of mycelium.

The time required to dry is highly dependent on the temperature and humidity of the environment you are drying in.
9. Add dried grains to your vented mason jars.  Fill to about ½ full if you intend to inoculate with a grain-to-grain procedure, or ¾ full if you intend to inoculate with a liquid or spore culture.   Don’t overfill on this step.  You’ll need space in the jar to allow for shaking or mixing later on during the colonization process. 
10. Install filtered lids on the jars.  Cover the lids with foil (optional). Filtered lids allow for gas exchange later on during colonization, but prevents contamination from entering the grain spawn. 

Aluminum foil prevents the grain from absorbing more water during the sterilization procedure. 
11. Place a trivet in the bottom of the instant pot. Jars can break if directly on the bottom of the instant pot.
12. Load the grain jars into the instant pot.
13. Add water to the instant pot to just below the bottom of the jars.   Water is necessary to create steam in the instant pot.  When water changes phase from liquid to vapor (steam) it expands approx. 1000x in volume; this is what brings the pressure up in the instant pot and allows for higher temperatures to sterilize the grain.
14. Install the lid on the instant pot. On older models, ensure the vent is turned to “sealing.” This ensures the pressure cooker will reach full pressure.
15. Pressure cook the jars:
  1. Press the “Pressure Cook” button on the instant pot.  
  2. Disable the keep warm feature by pressing the “Keep Warm” button and observe the keep warm indicator light turns off.  
  3. Press the “+” button until the display reads “1:30.” Allow the instant pot to start on its own. 

Sterilizing for 90 minutes ensures the grain is fully sterilized. 

Since this step is best performed overnight, disabling the “keep warm” function ensures the grain will be cool enough to inoculate in the morning.  Maintaining high temperature in the instant pot for prolonged periods of time may damage the grain. 

16. Allow the instant pot to come up to pressure and maintain pressure for 90 minutes as programmed. 

Allow the instant pot to cool overnight, or until cool to the touch. 
The grain must be approximately the same temperature as the donor spawn or liquid/spore solution in order to avoid shocking and killing the organism.
17. Remove the jars from the instant pot and proceed to inoculation.