Grain spawn

Grain spawn is the amplifier. A single culture becomes a jar; a jar becomes ten jars; ten jars inoculate enough bulk substrate to fill a shelf. Nothing else in the process multiplies like this.

It is also where most grows fail, for one reason: grain is the most nutritious thing in your process, sealed in a container, held at exactly the temperature contaminants like best. Everything that can go wrong here does so enthusiastically.

Choosing grain

Grain	Pros	Cons
Rye berries	The standard. Good size, colonises evenly, high yield	Costs more than birdseed
Millet	Enormous number of inoculation points per jar	Small; easy to over-hydrate
Wild bird seed	Cheap and available everywhere	Inconsistent; sunflower hulls go rancid
Oats	Cheap, colonise fast	Split easily, prone to going gluey
Popcorn	Cheap, large, easy to see through	Fewer inoculation points per jar

Rye if you can get it. Millet if you want maximum inoculation points. Wild bird seed if cost dominates and you are prepared for variability.

Hydration — the step that decides everything

Target roughly 45–50% moisture for grain. Wetter than that and you get bacterial contamination; drier and colonisation stalls.

Two methods:

Soak and drain. Cover with water, soak 12–24 hours at room temperature, drain thoroughly, then spread out and air-dry until the kernels are dry to the touch. This also lets some bacterial spores germinate so sterilisation kills them.

Simmer. Bring to a simmer for 10–15 minutes, drain, spread and dry. Faster, and more prone to splitting kernels — watch it.

Either way: the outside of every kernel must be dry to the touch before jarring. Free water in a jar is the single strongest predictor of wet spot.

Add gypsum at about 5% of dry weight. It keeps kernels from sticking together and buffers pH.

Sterilising

Not pasteurising. Sterilising.

15 psi, timed from when the gauge holds pressure — not from when you turned the burner on
90 minutes for pints, 120 minutes for quarts
Jars filled no more than two-thirds
Space between jars so steam circulates
Lids on but not fully tightened, or with filter patches

Bacillus endospores survive boiling comfortably. This is the entire reason grain requires a pressure cooker and straw does not.

Let jars cool completely — 8–12 hours, usually overnight. Inoculating warm jars kills culture and draws contaminated air in as the contents contract.

Inoculating

In a still air box or in front of a flow hood:

Liquid culture: 2–5 ml per quart, injected through the port at an angle.
Agar wedge: a piece from the leading edge, dropped in.
Grain-to-grain: 1 colonised jar into 5–10 fresh jars. Fastest by far, and it multiplies any contamination just as efficiently.

Alcohol on everything. Flame the needle. Minimal movement. Do not talk over open jars.

Colonising

70–78°F, in the dark. Grain does not need light and warmth beyond this range favours contaminants more than it favours you.

Shake at 20–30% colonisation. This is the single highest-leverage action in the whole stage — it redistributes mycelium through the grain and turns one colonisation front into hundreds. Expect roughly to halve total colonisation time.

Shake too early, with too little established mycelium, and you can set the jar back badly or kill it. Wait for visible white through a third of the jar.

Some growers shake twice. Once is usually enough.

Full colonisation takes 14–21 days for most species. Lion’s mane and shiitake run at the slow end.

Then let it consolidate

Once fully white, give it 3–7 more days. The mycelium binds the grain into a solid mass and builds reserves. Spawning immediately at 100% works, but a consolidated jar performs better.

Do not leave it indefinitely. Past about three weeks at full colonisation the grain starts to dry, metabolites accumulate, and vigour drops.

Reading a jar

White, dense, evenly advancing — healthy
Grey-brown gluey patches, sour smell — wet spot, bin it
Any colour: green, black, orange — see diagnostics, bin it
Amber droplets on healthy white — normal metabolites
Stopped at a clean line — suspect bacteria, smell it carefully

Fully colonised, consolidated grain goes to spawn to bulk.