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Ground Up Farms — Sterilization Fix: Decision Memo
Clara · 2026-09-25 · sources: Mike (farm mgr) + Grant (funding)
The problem
~30% substrate contamination is making the business unviable. Root cause: the current 55-gal drum cannot hold pressure (no autoclave seal; ceiling ~1.2 atm), so it runs atmospheric ~99°C for 8–18 hours and still loses ~30%. The missing piece is a pressure vessel — not a fuel change, not a redesign.
The volume
100 kg substrate/week → ~300 lb mushrooms/week → ~1.7 pressure cycles/week on a 150L-class vessel. One mid-size unit covers it with headroom.
The cost of waiting
A 30% loss at 300 lb/week ≈ $3,100–4,700/month (at $6–12/lb). Contamination also wastes spawn, labor and fuel, so the true loss is higher.
The options
| Option | Cost | Trade |
|---|
| All-American 941 (home canner) | ~$650 | NOT APPLICABLE — hobby scale (~39 L); T already owns a canner, and it is far too small for 100 kg/wk |
| Chinese vertical autoclave (uncertified) | $2–3.5K | Scale, but NO ASME — uninsurable, no recourse; needs safety retrofit |
| Used retort + matched boiler | $4–6K+ | Certified + scale, largest spend |
Committed pick: ONE 150L-class burner-fired (gas/LP) retort/vessel — T's sealed-vessel + burner plan, matching the gas drop-in. Fuel: burner-fired (propane/NG), NOT electric. Price: ~$2,000–3,500 FOB import + freight (not firm until the vendor is vetted).
Recommendation
- Buy the COMMERCIAL vessel — the committed 150L-class burner-fired (gas/LP) retort. Target is commercial throughput for 100 kg/week; hobby canners are out.
- Insulate. Aluminum jacketing cuts surface heat loss ~80–90% — a bigger save than upsizing. Insulate AFTER pressure-testing; keep the relief valve and gauge exposed.
- Payback: a ~$650–3,000 fix pays back in under a month. It is self-funding — no grant or savings required; finance it if needed.
Non-negotiables (every option)
- Certified pressure relief valve
- Pressure gauge
- Documented pressure rating (15–30 psi)
- Pressure test BEFORE first use
- Insulate only after testing; never cover the relief valve or gauge
Open items
- Mike: vessel vendor vetting; insulation retrofit; per-batch loss + fuel logging.
- T: confirm $/lb; is the 100 kg DRY or WET substrate (changes vessel size, not the verdict).
- T + insurer/state: requirements for running a pressure vessel commercially (unverified).
- Funding: USDA REAP loans open now (grants paused); ODOE/ORAEA covers 75% of an energy assessment. Solar+battery is a SEPARATE ~$120–160K project — not needed to fix contamination.