How to make grain spawn in jars at home

Creating grain spawn is one of the fundamental steps in mushroom cultivation. It involves growing mushroom mycelium in a sterilized grain substrate, which can later be used to inoculate bulk substrates. Here is an in-depth guide on how to prepare grain spawn using jars with self-healing injection port (SSIP) lids and a pressure cooker:

Materials Needed:

1. Whole grain (rye is commonly used, but you can use others like millet, wheat, corn).
2. Wide-mouth canning jars with SSIP lids.
3. Pressure cooker.
4. Mushroom spore syringe, liquid culture syringe, or agar wedge.
5. Large pot for boiling/soaking grains.
6. Strainer.
7. Distilled water.
8. Aluminum foil.
9. A clean working area, preferably a still-air box or in front of a flow hood.
10. Optional: Measuring cup and a scale.


1. Preparation of Grain: Measure out your grain. A general rule of thumb is to fill your jars halfway with grain. Rinse the grains thoroughly in cold water to remove any dust or debris, then soak them in a pot with enough water to cover them completely. Soak the grain for 12-24 hours to hydrate the kernels and to germinate any endospores present.

2. Cooking the Grain: After soaking, drain the grain and return it to the pot. Add fresh water and simmer the grains for about 15-30 minutes until they're hydrated but not bursting. You can test a kernel by cutting it open. It should be swollen and soft, but not mushy.

3. Drying the Grain: Drain the cooked grain using a colander and allow it to dry. This step is crucial as excess moisture can lead to contamination. Spread the grains out and let them cool and dry for an hour or so, until there's no visible moisture on the surface of the grains.

4. Filling the Jars: Once your grains are properly dried, fill your jars halfway. This leaves room for shaking and growth expansion. Do not pack the grains tightly into the jars.

5. Preparing for Sterilization: Screw the SSIP lids onto your jars and cover the lids with aluminum foil to prevent moisture from entering the injection ports or filter patches during sterilization.

6. Sterilizing the Grain Jars: Load your jars into the pressure cooker, being careful not to block the vent. Depending on the size of your pressure cooker, you may be able to stack jars, but ensure the cooker isn't overcrowded and steam can circulate freely. Follow your pressure cooker's instructions, bring it up to 15 psi, and maintain that pressure for 90 minutes to sterilize the grains.

7. Cooling the Grain Jars: Allow the pressure cooker to cool naturally. Do not force it open as this can cause a sudden pressure change and make your jars explode. Once it's completely depressurized and cool to the touch, you can open it, but leave the jars inside until they've cooled to room temperature. This can take several hours or even overnight.

8. Inoculating the Grain: In a clean area (still-air box or in front of a flow hood), remove the foil from a jar and shake your spore or liquid culture syringe to break up any clumps. Wipe the needle with an alcohol wipe, flame sterilize it, and then let it cool. Inject the required amount of spores or liquid culture into the injection port. Shake the jar to distribute the inoculant. Repeat for the remaining jars.

9. Incubation: Place your inoculated jars in a warm (75-81°F /

24-27°C), dark place and wait. Within a week or so, you should start seeing mycelial growth. Once the jars are fully colonized, they're ready to be used to inoculate your substrate.

Remember that maintaining sterility is crucial during all these steps. Any contaminants present in your grains, jars, or introduced during inoculation can outcompete your mushroom mycelium, ruining your batch.
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