The Mushroom Guide Part 4: preparing fruiting substrate for shiitake mushrooms

In Part 4 of The Mushroom Guide with Benedict Noel, learn how to create your own bags of fruiting substrate for shiitake mushrooms, using sawdust, bran and a pressure cooker.

In case you missed them, catch up with Parts 1, 2 and 3 first.

You’ll hear the word substrate used a lot in mushroom cultivation. Simply put, it’s the medium that your mycelium will be growing in. Usually, this will be some sort of natural waste product such as straw, wood chips, sawdust or even paper. When people refer to “fruiting substrate”, the intention of the substrate is to produce mushrooms. Alternatively you can produce substrate to expand it to more substrate rather than fruiting it directly.

To get started, at a minimum what you’ll need is:

• a pressure cooker
• a container to hold the substrate in (usually filter patch bags)
• a source of sawdust/wood chip, bran

Recipe

For most of my shiitake grows, I use eucalyptus sawdust (usually blue gum fines) and wheat bran for the substrate. Most kinds of hardwood sawdust will work well, ideally they’ve been aged a bit (not too green) and are a good size. I find that “fines” are an ideal size, but if you’ve got a mixture of coarse and really fine sawdust it works well too. If your sawdust is as fine as powder, it will get waterlogged and the mycelium will take a long time to colonise it as there isn’t enough air space between sawdust particles. If your sawdust is too coarse, there will be too much air space between particles affecting your yields and it’s also harder to pack into bags without puncturing them.

Hydration

Getting the right hydration for your substrate is very important. With either too much or too little water and your mycelium will take longer to colonise or your yields will be lower. It’s usually better keep your substrate on the drier side, as waterlogged substrate has a tendency to contaminate more easily. To test if your substrate has the right amount of hydration (known as field capacity), the recommended way is by doing a squeeze test. To do this, pick up a handful of the hydrated sawdust and squeeze it as tightly as possible. Only a few drops of water should drip out; more than a few drops and you’ve hydrated it too much. If there are still dry patches and no water coming out you’ll need to add a little more water.

Credit: The Mushroom Guide

For my setup, I find that a good ratio is 1kg of sawdust, 250g of wheat bran and 1.6L of water. For a typical dry sawdust you’ll need approximately 1.5L of water to 1kg of sawdust. If you’ve got a consistent supply of the same type of sawdust, a good way to work out the right amount of hydration is by using some kitchen scales. Get your scales and weigh out 100 grams of sawdust into a container and then add 100ml of water. Stir the mixture and keep adding a small amount of water (maybe 10ml at a time) and give it a squeeze each time you add water to see if it’s a field capacity. Once you’ve worked out the right ratio, you can use that ratio when you’re weighing out larger amounts. I find that bran only requires about 250-500ml of water to 1kg of bran.

Credit: The Mushroom Guide

Mixing and preparing bags

When making bags, I usually make 6 small bags at a time. This amount fits exactly into my All American 921 pressure cooker. Each bag contains 500 grams of sawdust, 125 grams bran and 800ml of water. I weigh out 3kg of sawdust into an esky (insulated foam container), add 750 grams of bran on top and then mix it thoroughly before adding 4.8L of water. Once I’ve added the water I mix it all together until there’s no water at the bottom of the esky. I then distribute the mix evenly into all 6 bags.

Credit: The Mushroom Guide

Credit: The Mushroom Guide

Credit: The Mushroom Guide

I stack the bags in the pressure cooker in two layers of three bags. I don’t seal the bags in any way, just fold them in on themselves with the filter patch facing upwards. Once you’ve pressure cooked the bags and let them cool, the bags will vacuum seal themselves as the pressure cooker loses pressure.

Coming up in the next post, we’ll cover the inoculation process.

Based on an original post available here by Benedict Noel at The Mushroom Guide.

About the author

The Mushroom Guide is written by Benedict Noel from Perth, Western Australia. He’s been hooked on mushroom growing since watching this TED talk in 2015 and has been building his knowledge and experience ever since. Since starting out, he’s helped run a couple of cultivation courses, given presentations at festivals and grown a wide variety of mushrooms, from oyster and shiitake to pioppino and chestnut.