Still Air Box: How to Build and Use One for Mushroom Growing

A still air box (SAB) is the cheapest way to work clean when you grow mushrooms. It is simply a clear plastic tub with two arm holes. Inside the box, the air does not move, so spores and bacteria settle down instead of landing on your work. In this guide, you will learn how to build a still air box, how to use it and when a flow hood is the better choice.

Why Sterile Work Matters

Most contamination comes from the air around you. Every movement stirs up dust, mold spores and bacteria. The box blocks that moving air. As a result, you can open an agar plate or a jar for a short time with a much lower risk of contamination. For beginners, it is the best first step before buying expensive equipment.

How to Build a Still Air Box

You only need a few simple items:

• A clear plastic storage tub of about 60 to 100 litres
• A marker and a tin can or round template of about 10 cm
• A heated knife, soldering iron or hole saw
• 70% isopropyl alcohol and paper towels

First, turn the tub upside down, so the lid becomes the floor. Next, draw two circles on the long side, about a hand width apart and halfway up. Then cut the holes slowly with the hot knife. Finally, smooth the edges so they do not tear your gloves. Some growers also add arm sleeves for an even better seal.

How to Use a Still Air Box Step by Step

1. Wipe the inside of the box with 70% alcohol.
2. Wipe every item you put inside, such as plates, syringes and bags.
3. Put on nitrile gloves and a face mask, then spray your gloves with alcohol.
4. Place your hands inside and wait a few minutes for the air to settle.
5. Work slowly and keep plates and jars open for as short a time as possible.

Safety tip: never use an open flame inside the box. Alcohol fumes collect in the closed space and can catch fire. Use pre-sterilized needles instead of flaming them.

What Can You Do in an SAB?

An SAB works well for small, quick tasks. For example, you can pour or inoculate agar petri dishes, transfer mycelium between plates, and load a syringe from a liquid culture vial. In addition, it is a good place to inject liquid culture into grain bags through an injection port.

Still Air Box vs Laminar Flow Hood

A still air box keeps the air still. A laminar flow hood, on the other hand, blows a constant stream of HEPA-filtered air over your work. That clean airflow pushes contaminants away, even while you move around. As a result, you can work in the open, keep plates open longer and handle larger batches.

• Still air box: very cheap and easy to build, but small and slow to work in.
• Flow hood: fast, roomy and very clean, but it costs more.

Many growers start with an SAB and upgrade once they make a lot of grain spawn or agar work. If that is you, have a look at our Envirco MAC 10 fan filter unit or the full range of laminar flow hoods.

Common Mistakes to Avoid

• Moving too fast: quick hand movements stir up the air inside the box.
• Skipping the wipe-down: every surface and item must be cleaned with alcohol.
• Working in a dusty room: do not work right after vacuuming or near an open window.
• Leaving lids open: open each plate or jar only for a few seconds.

Want to learn more about sterile work? Read our guide on growing mushroom cultures on agar petri dishes. For the science behind clean airflow, see the Wikipedia article on laminar flow cabinets.