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Spawn & Substrates
Brown Rice Flour
Organic wholegrain brown rice flour, the nutrient half of a classic PF Tek substrate. You mix it with vermiculite and water, sterilise it in jars, then grow from it.
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Resealable bag. Store cool and dry.
Milled from whole organic brown rice, no fungicides or pesticides
Feeds the mycelium where vermiculite only holds water and air
1KG or 5KG, keeps in a cool dry cupboard
The short version
Brown rice flour is the food source in a PF Tek mushroom substrate. On its own it is just flour, so it is always mixed with vermiculite and water, packed into jars, and sterilised before use.
Ours is milled from whole organic brown rice. It carries the carbohydrate and protein the mycelium feeds on, while the vermiculite around it holds moisture and keeps air pockets open.
What it is
What brown rice flour does
Brown rice flour is wholegrain brown rice ground to a flour. In mushroom growing it is the nutrient part of a PF Tek substrate. It carries carbohydrate, protein and trace minerals, which is what colonising mycelium feeds on.
It is never used alone. Flour on its own packs down dense and wet, which suits contaminants more than mushrooms. Mixed through vermiculite it stays open and airy, the vermiculite holds the water, and the flour coats each particle as the food source. Brown rice flour is used in place of white because it keeps the bran and germ, so it carries more nutrition.
How to use it
Making a PF Tek substrate
The standard PF Tek recipe is a 2:1:1 mix by volume: two parts vermiculite, one part brown rice flour, one part water. Most people work in half pint jars. As a per jar guide, that is about 120ml vermiculite, 60ml flour and 60ml water.
Wet the vermiculite
Mix the vermiculite with the water first and stir until it has taken up all the water it can. There should be no water sitting in the bottom of the bowl.
Add the flour
Stir in the brown rice flour so it coats the damp vermiculite evenly. The mix should clump when squeezed but release no free water.
Fill the jars loosely
Spoon the substrate into jars without tamping it down, stopping about a half inch below the rim. Loose packing leaves the air pockets the mycelium needs.
Dry top layer
Top each jar with a half inch layer of plain dry vermiculite. This sits between the substrate and the air as a barrier against airborne contamination.
Sterilise
Cover the jars and sterilise. In a pressure cooker that is 15 PSI, about 121C, for 60 to 90 minutes. By steaming instead, hold the jars in steam for about 90 minutes. Let them cool fully to room temperature before you open them.
A common mistake is too much water. If free liquid pools in the jar the mix turns to paste, packs airless and invites contamination. Aim for a mix that just holds together when squeezed. Quantities scale: a 1KG bag covers many dozen half pint jars, since each jar takes only a small measure of flour.
Storage and limits
Storage, and what it is not
Keep the bag sealed in a cool, dry cupboard. As a wholegrain flour it keeps the bran oils, which go off in time, so use it within a few months once opened rather than storing it for years. Reseal after each use.
This is a substrate ingredient, not a finished grow kit and not a sterile product as supplied. It still has to be mixed and sterilised before anything is grown in it. It is also not the same as whole grain spawn such as rye or brown rice grain, which is used at a different stage. Brown rice flour is for the fruiting substrate.
Common questions
Frequently asked
No. It is the food part of a substrate and must be mixed with vermiculite and water, then sterilised in jars before use.
The classic PF Tek mix is 2:1:1 by volume, two parts vermiculite to one part brown rice flour to one part water. Per half pint jar that is about 120ml vermiculite, 60ml flour and 60ml water.
Yes. Filled jars are pressure cooked at 15 PSI for 60 to 90 minutes, or steamed for about 90 minutes, then cooled fully before opening.
Brown rice keeps the bran and germ, so it carries more nutrition for the mycelium.
It suits the species usually grown by PF Tek, including oyster. Wood-loving species such as shiitake are not suited to this mix and need a hardwood sawdust substrate instead.
Reseal the bag and keep it in a cool, dry place. Use within a few months of opening, as the bran oils go off in time.
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Supplied for legal gourmet mushroom cultivation and microscopy use.
We work hard to keep this information accurate and to cite reputable sources, but the occasional mistake can still slip through. Always check the product label and a current reference before relying on any figure for something important.