How to produce sterile substrate
How
to produce sterile substrate, using
Mushroombox
Mycobags.
This document is not
the definitive method for producing sterile material, but can serve
as a basis from which you can develop your own procedures. No
responsibility is taken for failure. Please ensure that you assess
any risks involved and are competent to carry out this procedure
before attempting. You follow this procedure at your own risk!
What
you need:
Mushroombox mycobag
Pressure cooker
Substrate (eg oak
sawdust, straw etc).
Procedure
Place substrate in
the bag. Typically you would fill the bag between 1/3 and ½ full –
no more. For standard sized pressure cookers, you may need to use
less than this, in order to fit inside the pressure cooker. Place
the bag in a container so that there is no danger of it tipping over
(ideally in a sink or basin). Pour on boiling water until the
substrate is completely immersed and soaked-through. Some substrates
are highly-absorbent – in which case you'll need an excess of
boiling water to compensate.
Leave the
substrate to soak for a couple of hours, to make sure it's fully
hydrated.
Pour off the
excess water, taking appropriate precautions against scalding. Make
sure there is no residual water whatsoever – this is critical,and
one of the commonest mistakes. If you are using the same substrate
every time, you can establish through trial and error, the exact
amount of water to rehydrate the substrate without producing any
excess.
Fold the top of
the bag over a couple of times, expelling ALL of the air inside the
bag in the process. This is very important – make sure there is no
air left in the bag. You can tape the folded section to the body of
the bag with masking tape or autoclave tape to keep it from opening
after sterilisation
Wrap the bag in a
damp tea-towel (NB use an old tea towel, as it will more than likely
suffer damage during pressure-cooking)
Add about 25mm
depth of water to the pressure cooker, and place the tea-towel
wrapped bag of substrate inside the pressure-cooker, ensuring there
is adequate clearance for the lid to close properly, without
impeding the operation of the safety valves.
Place the
pressure-cooker onto the hob, and when the valve starts hissing
reduce the heat to a level that maintains a low but steady emission
of steam from the pressure-cooker.
Cook for a minimum
of 45minutes. For larger volumes inside the bag, you may wish to
increase the cooking time to a maximum of 2hours. You need to
provide sufficient time for sterilisation temperatures to be reached
in the centre of the bag, but not so much that you render the
substrate to a paste!
Turn off the heat
and remove from hob to cool fully to room temperature (this will be
several hours – so often best to leave overnight)
In a clean
environment (ideally a sterile air flow from a laminar hepa filter),
remove the lid, and remove the bag of substrate. Open the top of the
bag for as short a time as possible, add the mushroom spawn and
immediately seal the top with a heatsealer (or failing that, fold it
over and tape it closed.
Incubate the
substrate/spawn at the desired temperature until full colonisation
occurs.
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Mushroombox. All rights reserved. Not to be modified or distributed
without permission. For personal use only.Â
