Bought spawn costs $8–12 a pound. Made properly, it costs under $1. At two tubs a month that difference pays for a pressure cooker within a year, and it is the step that makes everything after it possible.
It also introduces the two things you have avoided so far: sterilisation and sterile technique. Expect your contamination rate to go up before it comes down.
What you need
| Item | Cost |
|---|---|
| Pressure canner, 23 qt | $100–180 |
| Wide-mouth quart jars, 12 | $20 |
| Lids with filter patch and injection port | $15 |
| Still air box — a tub and a hole saw | $20 |
| Rye berries, 25 lb | $25 |
| Gypsum | $8 |
| Liquid culture or spawn to start from | $15–25 |
The canner is the real purchase. Read pressure cooker sizing and use before buying — the electric multi-cooker question in particular, because most of them will not do this job.
The cycle
1. Prepare grain. Rinse, soak 12–24 hours, drain, surface-dry until every kernel is dry to the touch. Add gypsum at 5% of dry weight. Jar two-thirds full. Detail.
2. Sterilise. 15 psi, 120 minutes for quarts, timed from when the gauge holds pressure. Purge the air first. Cool overnight.
3. Inoculate. In a still air box. Alcohol everything, flame the needle, 3–5 ml of liquid culture per quart. Minimal movement, no talking.
4. Colonise. 70–78°F, dark. Shake at 20–30%. Full in 14–21 days.
5. Consolidate 3–7 days.
6. Spawn to bulk as before.
The two things that will go wrong
Timing sterilisation wrong. The clock starts when the gauge holds 15 psi. Not when the burner goes on, not when steam appears. This single error causes more wet spot than everything else combined.
Grain too wet. Tip the jar. If liquid moves, it is too wet. Surface-dry properly and this stops being a problem.
Both of these are boring, mechanical, and entirely within your control. Neither is a technique skill.
Sterile technique, briefly
- Still air box, wiped down, then wait 5–10 minutes for the air to settle before starting. The wait is the part that works.
- Everything you need goes in first.
- 70% isopropyl, not 91% — it penetrates better and evaporates slower.
- Flame the needle to glowing, let it cool a few seconds.
- Move slowly. Currents carry spores.
- Do not talk over open jars.
A still air box used patiently gets close to flow hood results for grain work. You do not need a flow hood yet — see SAB vs flow hood.
Grain-to-grain
Once you have a clean colonised jar, one jar inoculates 5–10 more. This is the multiplier that changes your economics entirely.
Use it for production runs from a verified clean jar. Do not use it endlessly — it multiplies contamination just as efficiently and accelerates culture decline.
What to expect
Contamination rate 20–40% on early runs, dropping to under 10% once sterilisation timing and hydration are habitual. If yours stays high, the cause is almost certainly one of those two rather than your technique in the box.
Time investment: an afternoon for prep and sterilisation, an hour for inoculation, then three weeks of waiting.
Cost per tub drops from $30 to about $5.
After
Working from liquid culture or bought spawn still means someone else controls your genetics. Working on agar means you control them.
Next: working with agar.
Sources
The works this page draws on. These are references, not pinpoint citations — see how sourcing works here.
- Growing Gourmet and Medicinal Mushrooms3rd ed., Ten Speed Press1993
- Organic Mushroom Farming and MycoremediationChelsea Green Publishing2014