Easiest way to make Master’s Mix mushroom substrate for high yield mushroom growth

What is Master’s Mix Mushroom Substrate

Master’s Mix mushroom substrate is a substrate medium that was developed by a well known mushroom cultivator T.R Davis at Earth Angel Mushroom ( check out his great mushroom growing videos here). A mycelium containing substance such as inoculated grain spawn can be added directly to the master’s mushroom substrate, which then provides the mycelium with an optimum source of nutrition for growing, colonising and then fruiting.

What mushrooms grow well on masters mix?

Nearly all types of mushrooms that would typically be grown on a straw or sawdust substrate with the notable exception of shiitake mushrooms. Some mushrooms that do experience success growing on masters mix substrate include:

A key reason behind the large adoption of the masters mix substrate within the mushroom growing community is its ease of production, as it contains only two main elements:

  • Soy Hulls
  • Hardwood Sawdust
  • * Both of these materials are often used in pellet form

How to make Masters Mix Substrate

The production of the master mix substrate has only two steps

  • Hydration of the substrate
  • Sterilisation of the substrate

After this has been completed it can be innoculated.

Hydration of the masters mix substrate:

The two components of the substrate ( soy and hardwood – pellet or dust) are combined together in a 1:1 ratio. This can be modified if you are trying to experiment, however this combination has been used countless times across the world with positive results. 

It is often useful to prepare the soy and hardwood pellets separately simply as the soy pellets can be much slower to break down from the pellet form into a usable hydrated form whereas the hardwood pellets this is achieved almost immediately with the addition of water.

2.5 cup of Soy Pellets + 2.5 Cups of Hardwood pellets + 1.4L of water is sufficient to fill one Large sized grow bag ( 50 cm x 20 x 12 ) 

Soy Pellets

  • For every 2.5 cups of pellets add 700ml of water
  • Allow this to soak overnight
  • Break apart pellets with clean hands

Hardwood pellets

  • For every 2.5 cups of pellets add 700 ml of water
  • Mix to break apart

After hydrating simply add these two components together, mix, and place inside of your grow bag. 

As an easier alternative to the above method, 2.5 cups of each source of pellets can be directly added to a large sized grow bag (50x20x12cm) with 1.4L of water and left to soak before breaking apart by massaging the bag. This method can be challenging if using Soy pellets that are particularly hard to break apart, so try testing with a couple of pellets and some water first.

Sterilization of the Masters Mix Substrate

There can be some confusion regarding the role of pasteurization and sterilization of mushroom substrates. Unfortunately using the incorrect method is almost certain to result in a high contamination rate, and a quick way to become discouraged with your harvesting. 

Oyster mushrooms in grow bag
Oyster mushroom in grow bag, src: https://www.youtube.com/watch?v=FdEz8iaHDsI&t=193s

To keep it simple, when using the master’s mix substrate, sterilization is a must, not pasteurisation. Failure to sterilize the substrate correctly will greatly reduce your ability to grow any mushrooms and greatly increase your contamination rate. Part of the reason for this is the high nutrient density of the substrate, in particular the soy hulls. Infact changing the ratio of the mixture to contain a higher proportion of soy hulls is also associated with an increase in contamination rates. While some mediums such as straw and coconut coir are naturally quite resistant to contamination (particularly bacterial contamination) and do not require as strict of a sterilisation process, the master’s mix does not have this benefit. As a result sterilization must be performed correctly, and the inoculation must be done using a sterile technique. While this may seem like a hassle, it is more than compensated for with the higher yields, and the development of good sterile techniques allows for greater success and more consistency with harvesting.

For at home hobby growers sterilization of the substrate can be achieved using a pressure cooker at 15psi for 90 to 150 mins. 

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