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A still air box (SAB) is the cheapest contamination control in mushroom growing, and one of the most effective. It’s a clear plastic tote turned upside down with two holes for your arms. It costs about $40 to build, takes about an hour, and handles agar, liquid culture and grain inoculation for most home growers.
Here’s how to build one, the mistakes that make a SAB useless, and how to work in it.
Why a Still Air Box Works
Mold spores and bacteria ride on moving air. Inside a closed box, once the air settles, almost nothing is floating around to land on your open plate or jar. A flow hood cleans the air. A still air box just stops it moving. That’s why your own movement is the biggest risk in a SAB, and why slow, calm hands matter more than anything you buy.
What You Need
| Item | Approx. price | Notes |
|---|---|---|
| Clear storage tote, 60 qt or larger | ~$40 | Clear is a must. Often cheaper at a local hardware store. |
| 4″ hole saw with arbor | ~$10 | For the arm holes |
| Drill | ~$65 | Skip if you already own one |
| Nitrile gloves | ~$10 | |
| 70% isopropyl alcohol | ~$29 | 70% works better than 91% or 99% for disinfecting |
| Painter’s tape, a marker, sandpaper | — | Household items |
Don’t want to build one? A pre-made still air box runs about $36 and works the same way.
How to Build It, Step by Step
- Flip the tote upside down. The lid becomes your work surface and the clear bottom becomes your window. This gives you a flat, wipeable base and a view straight down onto your work.
- Mark two arm holes on one long side. Place them about 3–4 inches up from the lid edge and about 8–10 inches apart, center to center. Sit in front of the box first and hold your arms where they’d naturally go. Your forearms should angle slightly down into the box.
- Tape before you cut. Cover each mark with a few layers of painter’s tape. Tote plastic cracks easily, and tape keeps the cut clean.
- Drill slowly. Run the hole saw at low speed with light pressure and let the teeth do the work. Pushing hard or spinning fast is how totes crack. (Some growers melt the holes instead with a heated metal can. It works, but do it outside, because melting plastic gives off fumes.)
- Smooth the edges. Sand or file the cut edges so they don’t snag your gloves or sleeves.
- Clean it before first use. Wash the inside with soap and water, then wipe every surface with 70% alcohol.
The 4 Mistakes That Make a SAB Useless
- Holes that are too big. Bigger holes mean more air rushing in every time you move. Four inches is plenty for most adult arms.
- A tote that’s too small. If you can’t fit your plates, jars and tools inside without stacking or reaching over things, you’ll contaminate work you can’t see.
- Fast movements. Every quick motion pumps room air in through the arm holes. Move like you’re underwater.
- Reaching over open work. Your arms shed particles. Keep open plates and jars to the side of your hands, never underneath them.
How to Work in Your Still Air Box
- Load everything first. Wipe each plate, jar, syringe and tool with alcohol and put it inside before you start. Getting up mid-session to fetch something lets room air in.
- Wipe down the inside with 70% alcohol and let it evaporate fully.
- Let the air settle. Close everything up and wait a few minutes so the air inside stops moving.
- Glove up and spray your gloves with alcohol. Wear long sleeves, or spray your forearms too.
- Slide your arms in slowly, then pause a moment before opening anything.
- Open things for as little time as possible, and keep lids facing down or close to the plate while open.
A safety note on flames: alcohol vapor is flammable. If you flame-sterilize a scalpel or needle, make sure all alcohol inside the box has fully evaporated first, and never spray alcohol while a flame is lit. Many growers flame tools outside the box, or use a fresh pre-sterilized blade instead.
When to Upgrade to a Flow Hood
A still air box can take you a long way. You’ll know it’s time to upgrade when the arm holes are slowing you down, you’re doing lots of agar transfers, or your contamination rate climbs as you scale up. When that happens, read our laminar flow hood buyer’s guide before you buy.
For everything else, from agar to grow bags, see the full equipment list.
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