How to make grain spawn to grow paddy straw mushroom

Posted by · March 04, 2022

Grain spawn can consider as "the seed" for growing mushrooms. It is made by inoculating sterilized grains with mycelium from an agar dish or liquid culture. Grain spawn can add to the substrate to grow paddy straw mushroom or propagate more mushroom cultures. Before sterilizing to kill live microbes, the process begins by cleaning, soaking overnight, cooking, and drying grains. For family cultivation, one or two spawn jars are more than enough. When it comes to a large scale of cultivation, each grain master jar can multiply more than a hundred times. Moisture content plays a vital role in fast mycelium run and reducing contamination.

Different types of grain spawn

Wheat, rye, rice, popcorn, brown rice, and wild bird seed are grains commonly used for making grain spawn. However, home growers prefer wild bird seeds for growing mushrooms since WBS is cheap and popular. You can easily find it at local pet stores.

Cleaning and soaking the grain

Rinse the grains with water four times to remove dust and undesirables and make sure the water is clear. Then soak the grain for 12-24 hours to allow the grains to absorb the water. Water soaking also helps reduce contamination since bacteria pathogens likely germinate and are killed through sterilization.

Cooking the grain

Add 1 liter of clean water, one teaspoon of Calcium carbonate (CaCO3), one tablespoon of brown sugar or molasses to 1 kg of grain. Calcium carbonate helps bring grain PH level to 7-8, at which paddy straw mycelium loves to run.

Cooking the grain to help the water penetrate through the center of grain and materials getting softer to allow faster digestion by the mycelium. Depending on the type of grains, cooking time is different. Cooking also helps wet grain dry faster.

Popcorn: cooking time is 15 minutes.
WBS - wild bird seed: cooking time 5 minutes.
Wheat grain: cooking time is 1 minute.

Drain and dry the grain

Pour the hot grain into a colander and shake well. Then spread the grains out in a thin layer over a towel or fly screen to allow the water to evaporate for 1 or 2 hours. Proper moisture content is around 40%. Before packing the grain into culture jars, make sure the grain becomes damp but not dripping wet. Grab a handful of grains for a few seconds and release, and you do not feel your hand getting wet.
Mix 1 tablespoon of gypsum to prevent the grains from sticking together and stabilize the PH level during mycelium running.

Pack, sterilize, and inoculate the culture.

Your grains are now ready for packing around ¾ of a mason jar, leaving ¼ on the top of each jar.
Drill or punch a ¼ inch hole on the lid and cover with microspore tape to allow gas exchange during spawn run.
Cover the jar lid with a piece of aluminum foil to prevent the water from spilling into your jar during pressure cooking.
Sterilize the grain jar at 15 psi for 90 minutes in the pressure cooker.
Let it cool naturally in the pressure cooker for a couple of hours.
Once the grain jar cooled down to 80-90 degrees Fahrenheit, your grains rea ready to inoculate culture, either from grain spawn or liquid culture.
For paddy spawn inoculation, open the lid and drop one or two tablespoon of spawn into the grain jar. Then shake well.
For liquid culture inoculation, inject a paddy culture syringe evenly around 2-5 cc into the wall of the grain jar via a 1/4 inch hole. Then replace the microspore tape with the new one or poly-fil.
For fast jar colonization, maintain temperature around 86-90 degrees Fahrenheit.
Paddy straw mycelium will colonize the whole jar around 1-2 weeks. If it is not ready to use, the paddy spawn can remain viable for 2-3 months when stored at 60-70 F.

Tips to reduce contamination

High moisture content is prone to contamination, and low moisture leads to slow colonization. Thus proper water content plays a crucial role in success.
Use aluminum foil to cover the jar lid to prevent moisture from escaping or entering the grain jar during sterilizing.
Always inoculate the grain jar in a sterile environment like a flow hood or still air box.
Clean hand and working table with isopropyl 70 alcohol antiseptic.