Still air box vs flow hood

What it is

Grain, agar and supplemented sawdust are rich enough that mould and bacteria grow on them quickly, so inoculating them calls for lab-like conditions¹. Straw, logs and wood chips are low in nitrogen and can be inoculated in open air with clean hands and a clean table¹.

UF/IFAS describes the two ways to get there. Labs work under a laminar flow hood, which blows filtered air across the bench; at home the authors suggest a still-air transfer box, which simply stops the air moving while you work². A commercial lab uses HEPA filters for the same reason¹.

A still air box is a clear plastic tote turned on its side or upside down, with two arm holes. A flow hood is a fan pushing room air through a HEPA filter so a steady stream of clean air flows toward you. The box costs little and fits on a shelf; the hood costs much more but gives you room to work at a normal pace.

What it suits

Every species. This is a workspace, so it matters for any tek that starts from agar, liquid culture or grain you make yourself.

Equipment

• Still air box: a large clear storage tote, a way to cut two arm holes, isopropyl alcohol spray, gloves
• Flow hood: a HEPA filter and matched blower in a housing, a sturdy table in front of it
• Either way: a flame or alcohol lamp for tools, parafilm or tape, a clean room with the windows shut

Time to first harvest

No harvest of its own. The box or hood is where you make cultures and spawn. Grain spawn inoculated this way colonised in about 10 to 20 days in the UF/IFAS method².

Contamination and other risks

• Airborne mould spores and bacteria landing on open plates, jars or bags. UF/IFAS recommends doing transfers inside a still-air chamber to limit this².
• Contamination from hands and sleeves. UF/IFAS strongly recommends gloves².
• Dirty tools. UF/IFAS flame-sterilises tweezers immediately before each transfer².

Steps, in overview

1. Set up. Shut windows and fans so the room air is still. Wipe the box or the bench in front of the hood with isopropyl alcohol.
2. Let it settle. Give the air a few minutes to stop moving before you open anything. With a hood, let it run first.
3. Work slowly. Gloved hands in, small movements, lids open as briefly as possible. Keep your hands downstream of the open plate or jar when using a hood.
4. Flame tools. Flame-sterilise tweezers or a scalpel right before each transfer².
5. Seal and label. Seal plates with parafilm or tape after inoculating² and write the date and strain on each one.

Common mistakes

• Cutting arm holes so large that air pumps in and out every time you move.
• Moving quickly inside the box, which stirs up the air you just let settle.
• Working behind the open dish in a flow hood, so air passes over your hands before it reaches the culture.
• Lighting a flame while alcohol from your wipe-down is still evaporating.