Contamination is any organism in your grow that is not your mushroom. It arrived on a particle of air, a dirty needle, a hand, or inside a culture that was never clean. Most of it is easy to identify once you have seen it, and the response is almost always the same: seal it, bin it outside, and work out how it got in. What you should never do is open a contaminated bag indoors to "check", because that is how one bad bag becomes six.

The usual suspects

Green mould (Trichoderma)

The big one. Starts as white, fast, fluffy growth that is easy to mistake for mycelium, then turns forest green in patches as it sporulates. Aggressive, fast and spreads by spores. In a sealed grain bag or substrate: bin it immediately. On agar: cut away from it fast or bin the plate. Favours warm, wet conditions and substrate that was not fully sterilised.

Blue-green mould (Penicillium)

Blue-green to grey-green, often with a white edge, and a musty smell. Slower than Trichoderma but just as terminal in a bag. Bin it.

Black pin mould (Rhizopus, Mucor)

Grey fuzz that grows fast and tall with tiny black dots on the tips. Loves warmth and high humidity. Bin it.

Black and yellow mould (Aspergillus)

Powdery black, yellow or green patches. Some species are a respiratory hazard: do not open, bin sealed.

Orange or pink bread mould (Neurospora)

Bright orange to pink, extremely fast, and it will escape through a filter patch that was weak. Bin it in a second bag, outside.

Bacterial wet spot

In grain: kernels that look wet, grey or translucent, often slimy, with a sour, rotten smell at the filter. The mycelium will not grow across them. Caused by bacteria that survived sterilisation or came in on the syringe. Bin the bag; test the culture on agar.

Cobweb (Dactylium / Hypomyces)

Grey, wispy, cobweb-like growth that spreads across a fruiting surface in a day and collapses pins. Looks like mycelium but greyer, thinner and much faster. Usually appears in fruiting tubs with stale, very humid air. A small patch can sometimes be treated with 3% hydrogen peroxide; a large one means the tub is finished.

Lipstick mould (Sporendonema)

Pink to red, slow, chalky. Rare in sealed bags, seen on exposed casing and old blocks. Bin.

Yeast

Glossy, round, cream-coloured dots on agar or a sheen on grain, often with a fermented smell. Bin and test the culture.

Is it contamination or mycelium?

• Mycelium is white, advances in an even front, and smells clean, earthy or like mushrooms. Metabolites can stain it yellow where it is stressed; that is not contamination.
• Colour of any other kind is contamination, full stop. Green, blue, black, grey fuzz, orange, pink.
• Texture: mycelium is fibrous and knits kernels together. Contaminants are powdery, slimy, wet or cobwebby.
• Smell: sour, sweet-rotten, musty or sharp means something else is living there.
• Speed: anything that visibly spreads in a day on a bag is not your mushroom.

What to do with a contaminated bag

1. Do not open it

   Sealed, it is harmless. Opened indoors, it releases millions of spores.

2. Double bag it

   Put it in a bin liner, tie it, and take it to the outside bin.

3. Clean the area

   Wipe the shelf and anything near it with 70% alcohol. If it was in a tub, wash the tub with hot soapy water and bleach.

4. Find the cause

   Which step let it in? A culture that was never tested, an unflamed needle, an open bag outside the still air box, a substrate that was pasteurised rather than sterilised.

Preventing it

Start sterile

Fully sterilised grain and substrate in sealed filter-patch bags. The difference from pasteurised is exactly this.

Test the culture

A drop of any new liquid culture on a low-nutrition plate shows bacteria in days.

Flame and wipe

Needle flamed to glowing, port wiped with alcohol, every single time.

Keep bags closed

Open bags only inside a still air box or in front of a flow hood, for seconds. SAB guide.

Spawn heavier

A 1:2 ratio colonises before contaminants can establish. Ratio guide.

Fresh air in fruiting

Stale, saturated air grows cobweb and bacteria. Air changes several times a day.

Harvest on time

Overripe mushrooms dump spores that feed the next contaminant.

Separate dirty and clean

Do not store spent blocks or compost near colonising bags.

Written by the Aus Myco Kingdom crew. Everything here is general growing information for gourmet and medicinal species; your room, your climate and your culture will have the final say.