Urban Spore

How To Make Grain Spawn

oyster mushroom grain spawn

What Is 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.

mycelium growing on grain spawn

How Is Grain Spawn Made?

Grain spawn is produced by growing and expanding a mycelium culture on grain. This process begins by hydrating grains overnight before sterilising in a pressure cooker.

The sterilised grains are inoculated with a live mycelium culture. This culture is usually grown on agar in a petri dish or purchased in a liquid culture syringe, alternatively the spawn can be inoculated with a portion of fully colonised spawn from a prior batch.

This grain spawn can take anywhere between 10 days to 3 weeks before fully colonised and ready for use.

Grain Spawn
Available Internationally

Commission earned from qualifying purchases.

What You'll Need

Grain spawn will require the use of mushroom grow bags or mason jars with modified lids. Lids are modified with a filter to allow for fresh air exchange. We recommend using mason jars for a higher success rate.

The weight of the grain will increase by approximately 60% after rehydrating. 1 kg of grain will yield approximately 1.6kg of grain spawn.


Save time & money with ready made spawn jars. Each jar features a specially modified lid for the production of grain spawn. 

Ready made spawn jars contain highly nutritious, sterilised, whole oats ideal for producing your own grain spawn for mushroom growing.

Can You Use An Instapot For Mushroom Growing?

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 Grain

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.

oats for making grain spawn

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.

Modified mason jar lids make the production of mushroom grain spawn and liquid culture a breeze. <br><br>Each lid features a filter patch for fresh air exchange and reusable injection ports for easy inoculation with a liquid culture syringe.

Step 3. Pack & Seal 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.

brf cakes

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.

The Presto 23 Quart Pressure Canner is an excellent option for sterilising media for mushroom growing.<br>It has capacity for sterilising up to 24 x half-pint mason jars.<br><br>Note: Using pressure canners for mushroom growing may void the warranty.

Step 5. Inoculate

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.

Alternatively, the lids can be briefly removed to allow for inoculation with a wedge of colonised agar.

spawn lids

Liquid culture is a powerful tool in the mushroom growers arsenal. Just a few drops is enough to start the transformation from sterilised grain to vigorous mushroom grain spawn. Liquid culture can be used to inoculate agar plates, grain spawn or even create an endless supply of liquid culture.

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.

mycelium growing on grain spawn

Other Articles You May Like

Hello From Luke

Thank you for visiting! This website is user supported. As an Amazon associate I earn from qualifying purchases.


“Radical Mycology is a must for believers, and an end for non-believers. Peter McCoy indulges the reader into the depths of the mystical, spiritual, technical and practical aspects of all things fungal in one of the most elaborate mycological reads I’ve ever come across.” – Giuliana Furci

Popular Articles

Essential Articles

Sterile Media

Save time & money with pre-sterilised media for mushroom growing.