How To Make
Grain Spawn

Learn How To Make Mushroom Grain Spawn

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What Is Mushroom Grain Spawn?

Grain spawn is a little known secret weapon of the world of mushroom cultivation. It’s made from sterilised grains that have been inoculated with a live mycelium culture.

Grain spawn contains a lot of energy for mycelium to consume. It’s a bit like rocket fuel for mushrooms. Once it’s added to your substrate it takes off like wild fire. 

Mother Nature works her magic using spores but in a controlled environment you need to tip the scales in your favour by using clean high-quality grain spawn so you are doing your best to ensure success.

How Is Grain Spawn Made?

The process of making grain spawn can take up to 3 weeks with the majority of the action requiring just a few hours of attention.

The process involves hydrating and sterilising grains in jars sealed with a filter patch for fresh air exchange.

Once sterilised the jars are to be inoculated using either an agar culture, liquid culture or grain spawn from a prior batch. This process is to be done using aseptic technique.

The inoculated jars of grain will require between 2 – 3 weeks to fully colonise before use.

What You'll Need

To make grain spawn you will need mushroom grow bags or reusable culture jars. Below I have listed what was used in our video tutorial but you may use the grains of your preference.

Can I Use An Instapot?

It’s not essential to have access to a stove-top pressure cooker or canner. An instapot or electric bench-top pressure cooker can be used instead. 

An instapot will often only reach approximately 7 – 8 PSI and for this reason sterilisation times for preparing grain spawn may need to be extended by 30 minutes.

A typical instapot will fit 4 spawning jars per cycle.

Step 1. Hydrate The Grains

Bring a large pot of water to the boil. Turn off and add the whole oats. Allow to soak for 1 hour. 

The time required for hydrating the grains may vary depending on the grain used. Firmer grains may require more time. Adjust accordingly.

The grain should be soft enough to crush between 2 fingers with slight resistance. I like using whole oats as they are firm enough to maintain their structure while expanding with a large starchy core.

Step 2. Drain The Grains

Drain the grains. An old fly screen can be used as an alternative to a sieve. Spread out the grains evenly to help them dry. Alternatively a table can be used with an absorbent cloth placed across it. The grains should still be damp but not dripping wet before moving onto the next step. This may take between 20 minutes – 1 hour depending on the weather.

grains for mushroom growing
How To Make Grain Spawn

Step 3. Pack & Cover Jars

Pack the slightly damp grain into reusable culture jars until they are two-thirds full. Leave space in the top of each jar.

Firmly cover each jar with a piece of aluminium foil.

Step 4. Sterilise

The grain jars can now be sterilised for a minimum of 90 minutes at 15PSI.

An instapot or electric benchtop pressure cooker can be used for sterilising. They will usually run at a much lower PSI, for this reason sterilising times may need to be extended by 30 minutes.

Step 5. Inoculate With Mycelium Culture

Once the jars have cooled down they are ready to be inoculated with either liquid culture or agar.

The sterilised media is highly nutritious and susceptible to contamination. For this reason it is important to inoculate using aseptic technique.

If possible a flow hood should be used. Alternatively, you can undertake inoculations in a enclosed space with minimal airflow, such as a bathroom. 

Prepare the work space and syringe before removing the layer of aluminium foil. Using an open flame sterilise the needle and inject a few CCs of liquid culture via the silicone injection port of each jar. Flame sterilise the syringe between each jar.

Aseptic Technique

It’s important to adhere to aseptic technique when inoculating grain spawn. Sterilised media is extremely prone to contamination.

Only objects that have been flame sterilised may make contact with the sterile media or culture. 

Alcohol can be used to sanatise and clean surfaces of micro-particles but is not suitable for sterilisation.

A face mask should be worn at all times. All work should be undertaken with a laminar flow hood when possible. In the absence of a flow hood a smaller enclosed space with minimal airflow, such as a bathroom may be used with varied results.

Step 6. Rest Jars, Shake & Wait

Once the mycelium has colonised 50% and 70% of the grain you may wish to shake the jar or bag of grain spawn. Doing so assists in dispersing the mycelium evenly throughout increasing colonisation speed.

Maintain at room temperature, darkness is preferred but not essential. The grain spawn should be ready for use within 14 – 21 days. 

Sterilised Spawn Bags

Each sterilised grain spawn bag has been carefully prepared by hydrating whole oats in a gypsum bath for 24 hours before sterilisation. 

The bag itself features a 0.2 micron filter patch to facilitate fresh air exchange without the contents becoming contaminated. 

Additionally, the self healing injection port allows the user to simply inoculate the grain using a liquid culture syringe with minimal risk of contamination.

Sterilised grain spawn bags make it possible to produce your own mushroom grain spawn without the use of a pressure cooker.

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