Contamination reference

Compare a suspect bag against these examples before you mark it. When in doubt, isolate the bag and check again in 24 hours.

Healthy mycelium

Normal growth

Healthy

Overview: healthy colonized bag

Close-up: rhizomorphic strands

Look: Bright white. Either ropy, branching strands (rhizomorphic) or even, cottony fluff (tomentose). Spreads outward from the inoculation point.
Smell: Earthy, like fresh mushrooms. No sour or sweet notes.
When: Visible within 3–7 days and grows steadily until the bag is fully white.
Note: Blue staining where the bag was handled is bruising, which is normal in Psilocybe species.

Nothing to do. Log the colonization progress and keep conditions steady.

Trichoderma (green mold)

Trichoderma spp.

Discard

Overview: Trichoderma patch on a bag

Close-up: powdery green spores

Look: Starts as a dense white patch, often mistaken for mycelium, that turns forest-green and powdery within 1–3 days.
Smell: Musty and damp, like a basement.
When: Most often on the casing or surface during late colonization or fruiting.
Test: The green colour is the test. Healthy mycelium never turns green.

Do not open the bag indoors. Seal it in a second bag, remove it from the room and sterilize the shelf. Flag siblings from the same grain jar.

Cobweb mold

Hypomyces / Dactylium

Treat early

Overview: cobweb mold on the surface

Close-up: grey wispy growth

Look: Grey, wispy and very fine, like a cobweb. Grows above the surface and can cover a bag overnight.
Smell: Usually little or none.
When: During fruiting, when humidity is high and fresh air exchange is low.
Test: Mist with 3% hydrogen peroxide. Cobweb collapses; healthy mycelium does not.

If it is a small patch, spot-treat with hydrogen peroxide, then increase fresh air and lower humidity. If it returns or spreads, discard the bag.

Bacterial wet spot

Bacillus spp.

Discard

Overview: wet, slimy grain

Close-up: cloudy grain kernels

Look: Grain looks wet, slimy or cloudy, grey to yellow-brown. Mycelium stalls and does not grow into it.
Smell: Sour, like rotten fruit or old socks. Often the first sign.
When: In grain jars and early colonization, usually from grain that was too wet or under-sterilized.
Test: Smell the filter patch. A sour odour with stalled growth is enough to confirm.

Discard the jar or bag. Check grain prep: soak, simmer and dry to field capacity, and confirm full sterilization time.

Contamination reference

Compare a suspect bag against these examples before you mark it. When in doubt, isolate the bag and check again in 24 hours.

Healthy mycelium

Normal growth

Healthy

Overview: healthy colonized bag

Close-up: rhizomorphic strands

Look: Bright white. Either ropy, branching strands (rhizomorphic) or even, cottony fluff (tomentose). Spreads outward from the inoculation point.
Smell: Earthy, like fresh mushrooms. No sour or sweet notes.
When: Visible within 3–7 days and grows steadily until the bag is fully white.
Note: Blue staining where the bag was handled is bruising, which is normal in Psilocybe species.

Nothing to do. Log the colonization progress and keep conditions steady.

Trichoderma (green mold)

Trichoderma spp.

Discard

Overview: Trichoderma patch on a bag

Close-up: powdery green spores

Look: Starts as a dense white patch, often mistaken for mycelium, that turns forest-green and powdery within 1–3 days.
Smell: Musty and damp, like a basement.
When: Most often on the casing or surface during late colonization or fruiting.
Test: The green colour is the test. Healthy mycelium never turns green.

Do not open the bag indoors. Seal it in a second bag, remove it from the room and sterilize the shelf. Flag siblings from the same grain jar.

Cobweb mold

Hypomyces / Dactylium

Treat early

Overview: cobweb mold on the surface

Close-up: grey wispy growth

Look: Grey, wispy and very fine, like a cobweb. Grows above the surface and can cover a bag overnight.
Smell: Usually little or none.
When: During fruiting, when humidity is high and fresh air exchange is low.
Test: Mist with 3% hydrogen peroxide. Cobweb collapses; healthy mycelium does not.

If it is a small patch, spot-treat with hydrogen peroxide, then increase fresh air and lower humidity. If it returns or spreads, discard the bag.

Bacterial wet spot

Bacillus spp.

Discard

Overview: wet, slimy grain

Close-up: cloudy grain kernels

Look: Grain looks wet, slimy or cloudy, grey to yellow-brown. Mycelium stalls and does not grow into it.
Smell: Sour, like rotten fruit or old socks. Often the first sign.
When: In grain jars and early colonization, usually from grain that was too wet or under-sterilized.
Test: Smell the filter patch. A sour odour with stalled growth is enough to confirm.

Discard the jar or bag. Check grain prep: soak, simmer and dry to field capacity, and confirm full sterilization time.

Healthy mycelium

Trichoderma (green mold)

Cobweb mold

Bacterial wet spot

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Healthy mycelium

Trichoderma (green mold)

Cobweb mold

Bacterial wet spot