Common contamination signs in mushroom culture work

A clean plate gives you a record of what happened after a transfer. If a new patch appears away from the intended growth, set the plate aside and record when you first noticed it. A photo and date help more than trying to name an organism from one color.

Mold-like growth

Fuzzy or powdery patches can develop green, black, or other pigment as they mature. Growth that starts at a plate edge may point you toward a seal or handling step, but the position alone does not prove the cause. Avoid opening a suspect plate on the clean bench to take a closer look. Keep it closed while you decide how to discard it.

Wet or spreading patches

Bacterial contamination can appear as wet, shiny, or spreading growth around a transfer. Grain may look slick or develop an unusual odor. Smell is a poor diagnostic method because opening a contaminated container can spread material. Use your visual record and review how the grain, tool, and culture entered the container.

Yeast-like colonies

Smooth, creamy colonies may appear on a plate. They can look different from the mycelium you intended to grow. Appearance gives you a reason to separate the plate from clean work; it does not establish a species or a single source of failure.

Trace the handling sequence

Write down the sequence before changing equipment. Note the culture source, sterilization cycle, cooling time, bench setup, tool handling, and when the container stayed open. If multiple plates from one batch show the same problem, compare the shared steps. If one plate fails after a single transfer, focus on that transfer.

A fan filter unit can lower the amount of airborne material reaching an open work area. It cannot correct a contaminated source culture or a tool that crosses the clean air path. Work on the handling step you can identify before replacing an entire bench.

For work involving hazardous organisms, use appropriate containment and training. A clean-air bench is built to protect material being handled, not the operator. CDC distinguishes clean benches from biological safety cabinets.