Growing Mushrooms At Home Growth - Part 2: Growth Medium

Recap

Part 1 presents a general overview of growing mushrooms at home. In this part, we create a hospitable environment for mushroom spores to sprout mycelia.

Decision 1 : Brown Rice Flour Cakes or Grain Span

Brown Rice Flour Cakes (BRF) are the original approach. They are

• reliable,
• a bit easier to keep clean,
• can get you to fruiting a bit quicker,
• are more likely to clog syringes,
• store for much longer than grain,
• require less work before fruiting
• generally produce lower yields

Grain Spawn

• requires rigorous sterilization,
• requires using a pressure cooker (an InstaPot is unreliable),
• requires the use of bulk substrate (which, while optional for BRF, does increase yield at the expense of adding 2 - 3 weeks additional growing time)
• requires a bit more handling before fruiting
• results in better yields (and better looking mushrooms in my experience)

Most people advise starting with BRF because they are more forgiving. Once you’ve managed to be successful with that, move on to working with grain spawn. That’s the approach I took, and if that is your interest, look up “PK Tek”, or here’s a good pk tek guide.

However, this guide will be for creating grin spawn as that’s my current favorite way to work. What finally made my decision was based on an experiment around inoculation, which is one place I’ve had a few issues.

Preparing Grain Spawn

In a nutshell

• rinse grain until there’s clear runoff
• soak the grain for several hours (4 - 20 for the grain we’ll be using)
• soft-boil the grain until clear, and you can crush it with your fingers
• strain water and let air dry until individual grains dry to touch
• place in grain jars to no more than 3/4 filled
• sterilize in a pressure cooker for 90 minutes (for 32 oz jars)
• slowly cool jars to room temp
• inoculate and wait

What You Need

• Palouse Brand Hard Red Wheat Berries.
• a pot to hold the wheat berries (better if you can later boil in that same pot)
• gypsum (optional)
• used coffee grounds (optional - and used is required, caffeine will slow/stop mycelium growth)
• stove
• pressure cooker
• strainer

Steps in Detail

rinse grain

• Measure out the dry grain by filling one of your jars 3/4 full (approximately). When soaked, the grain nearly double in size.
• Rinse the grains until the runoff is clear.

I use a colander lined with paper towel so the smaller grains don’t slip through.

soak the grain

• Soak the grains for several hours (4 - 20 for the red wheat berries. Long enough to fully absorb water, but not so long that it begins to sprout. Sprouted grain is more likely to invite contamination.)
• (Optional, but recommended) Gypsum (1 TBSP per 32 oz jar you’ll be creating). The gypsum helps to keep the grains from sticking together.
• (Optional) Include used coffee grounds (1 TBSP per 32 oz jar you’ll be creating).

I use a stove-top pot for this step. After soaking, bring the pot to a slow-rolling boil. This keeps the gypsum and coffee grounds through more of the preparation time.

These optional ingredients are a mix from several sources. I do not know for a fact that either of these help, but I’m happy with my actual results, so they do not seem to hurt.

And even though I keep saying 32 oz. jar, remember that means it’s only filled to 3/4.

soft-boil the grain

The goal from this step is to make the grain easy to crush with your fingers, but still intact. If you happen to be using malted grain, recent experience suggests that you should skip this step as the grain is already sufficiently soft from the malting.

• Bring the grain along with its water to a soft-boil
• Stir gently and check to see if the grains are easy to crust between your fingers (10 - 20 minutes)
• Immediately remove from heat, strain and rinse with cold-water to stop further cooking

strain water

Allow the cooled grains to strain for several hours. The grains have absorbed water and nutrients internally. Now, you want the grains dry to the touch to avoid having too much moisture (invites contamination) in the jar.

Dry grains also tend to stick together less, making later steps a bit easier.

place in grain jars to no more than 3/4 filled

Fill your mason jars to 3/4 full. You need room to shake the grains later. Less is fine.

Seal the jar lid with aluminum foil. I take a square of foil and fold it twice. The foil protects the filter on the lid, and keeps steam out of the jars.

Reminders

• the lids of your jars have holes punched in them
• those holes are covered by a filter (synthetic, poly-fill, medical tape)
• you’ve covered the lid with aluminum foil to protect the filter, and to keep steam out of the jars during sterilization.

sterilize

Assuming 32 oz mason jars, you’ll want to pressure-cook for 90 minutes. 60 minutes for 16 oz and smaller. If you use a larger mushroom bag, at least 2 hours.

• Put a wire wrack on the bottom of your pressure cooker (the bottom is hot, and will likely break your mason jars)
• Put the jars on the wire-rack
• Fill the pressure cooker according to its instructions, but that should mean to at least the bottom 1/3 of your jars
• Check that the water level isn’t so high as to make the jars nearly float
• Seal and start heating
• When you’ve reached 15 PSI, start a 90-minute timer
• Take from heat and let slowly cool (I do so over a minimum of four hours, but typically over-night)

inoculate and wait

Here’s what I’ve started doing as of 2022/July.

• Jars are cooled and the aluminum foil cover removed
• Jar lids have 3 - 4 holes each
• Each hole is covered by a 20 mm synthetic filter
• Place jar on well-lit counter
• Have a spare synthetic filter handy
• Fill shot glass with 99% isopropyl alcohol
• Lightly dip cotton swab in shot glass
• Rub one synthetic filter with the wet cotton swab
• If this is your first use of a spore syringe, remove sterile needle from its pack, remove the cap on the syringe, twist the needle in place
• Unscrew the plastic cover from spore syringe
• Use a butane torch and bring bottom quarter of the needle to red-hot
  • If you have an alcohol lamp, use this instead, as it’s more gentle
• Immediately douse needle in shot glass
• Pierce the swab-rubbed synthetic filter with needle
• Inject approx 2 - 2.5 ml / 32 oz jar (that is 3/4 filled)
• Remove needle and place it back in the shot glass
• Immediately add new filter on top of pierced filter

Prepare Jars for Medium

I’ll be using 32 oz mason jars, but pick a jar size that fits your pressure cooker.

What You Need

• Mason jars with lids
• Synthetic Filter Paper Stickers
• Nail and Hammer
• Cardboard
• Scissors

What to do:

• Nail 3 holes into the lid
  • large enough to allow a syringe needle to fit
  • placed so when covered by a filter, the filters won’t touch the edge, or each other (you’ll be able to reuse longer)

One way to do this:

• Cut 8 4” x 4” cardboard squares
• Place a mason jar lid, top down, on the stack of cardboard squares
• Use a hammer and nail to punch a hole in the lid

Still Air Box

You can build an inexpensive still-air box, and having it makes reliability go wy up. If you can afford a flow-hood, even better. I have ended up with a flow-hood-modified still-air box.

What you need

• Still Air Box (see below)
• 99% isopropyl alcohol
• Professional Spray Bottle
• UVC Light

Build a Still Air Box

• Large clear plastic storage container
• Still Air Box Port Kit
• Drill
• 4.5” hole saw (4.25” in my case, and a Dremel to extend)
• 8 pieces of 6”x6” cardboard
• Ability to use said drill

Time

• 1 hour to build the still air box (1 time only, you’ll get a lot of use out of this)