Spawn Preparation

Penn State Spawn Lab Procedures for Making Spawn

In the spawn-production process, mycelium from a mushroom culture is placed onto steam-sterilized grain, and in time the mycelium completely grows through the grain. This grain/mycelium mixture is called spawn, and spawn is used to “seed” mushroom compost.


250 ml Flasks
50 ml beaker level full of rye grain
1/2 tsp. Calcium Carbonate, powder (lime)
1/4 tsp. Calcium Sulfate (gypsum)
60 ml warm water

Autoclave 35 minutes at 121°C - Fast Exhaust
1000 ml Flasks
250 ml beaker level full of rye grain
2 tsp. Calcium Carbonate, powder (lime)
1 tsp. Calcium Sulfate (gypsum)
220 ml warm water

Autoclave 45 minutes at 121°C - Fast Exhaust 


Shiitake mushrooms are produced from spawn which is the vegetative growth or pure culture mushroom mycelium on a suitable sterilized substrate such as various agars, grains or wood chips. Formulas listed below were developed for use in producing spawn for synthetic logs. Synthetic logs are usually produced by autoclaving supplemented wood chips in heat-resistant plastic bags containing a breather strip then aseptically inoculating the cooled substrate with spawn. We have successfully produced shiitake mushrooms from synthetic logs inoculated with spawn manufactured as outlined below. 

500 ml Flasks
100 ml beaker level full of rye grain
50 ml beaker of hardwood sawdust
1/2 tsp Calcium Sulfate (gypsum)
120 ml of warm tap water
1000 ml Flasks

250 ml beaker level full of rye grain
100 ml beaker level full of hardwood sawdust
1 tsp Calcium Sulfate (gypsum)
230 ml warm tap water
Use cotton plugs and paper bags over plugs and autoclave for 45 minutes at 121°C - Fast Exhaust  



In making spawn for Pleurotus, substitute same amount of Calcium Carbonate (lime) INSTEAD of Calcium Sulfate (gypsum).