Mycelium metabolites or mushroom pee

Yellow mycelium or Yellow liquid on mushroom mycelium: contamination or mycelium piss

Sometimes you can observe healthy mycelium with small amount of clear yellow, yellowish, orange or brown liquid forming on the surface of the mycelium. Examples in short video:

It can be noticed in spawn jars during colonisation period.

Yellow liquid appeared on the mycelium, mycelium turned a yellowish color, strange yellow-brown line appeared on the mycelium. What could it be? Contamination or mycelium metabolites aka mycelium piss?

It can be noticed on mushroom cake during top layer colonisation or fruiting period

What is it? Is there something to worry about?

What are mushroom metabolites

Secondary mycelium metabolites (aka mycelium exudate, mushroom urea, mycelium piss, mycelium pee) — it is a waste products of fungal metabolism or mushroom exudate.

🔬 Biochemical analyses of the exudates showed that acid phosphatase, β-glucosidase, acid and alkaline protease, RNase polygalacturonase and cellulase enzymes as well as oxalic acid and ammonia were present

In short and simple metabolites consist of acids, exopolysacharides, waste products and antibiotics, which are naturally secreted by mycelium cells. They can be found on different species of mushrooms: wild mushrooms, magic mushrooms, gourmet and edible mushrooms.

Metabolites are the natural immune response of mycelium to stress or pathogens.

Symptoms of mushroom piss

✅ Color of liquid: yellow, orange or brown

✅ Liquid is transparent

✅ NO slime

✅ NO smell, except smell of bulk substrate and mushrooms.

Main causes of mycelium metabolites

Metabolites is a reaction to environmental stress or immunity response to contaminants:

🆘 over misting, water pools on mycelium

🆘 direct sunlight

🆘 high temperature

🆘 extremely dry mushroom cake

🆘 aged mycelium (aged spawn jars)

🆘 lack or excess of nutrients in the substrate

🆘 a symptom that mycelium is fighting with pathogenic microorganisms (bacteria, mold)

🆘 this also happens if you mix several strains of mushrooms. Their colonies struggle with each other and create yellow/brown borders between them

🆘 stroma and overlay are accompanied by mushroom pee

🆘 mycelium tissue damage

🔴 Recommended: Fruiting period. Pinhead initiation. Growing parameters for Psilocybe Cubensis

What is the strange yellow-brown line on the mycelium

Let's figure out one case from Shroomok Discord Community. This is a great example to show you metabolites sectoring.

Question: Strange yellow-brown line on the mycelium. Anyone know what this could be?

Answer from Shroomok:

Here are mushroom metabolites and sectoring process. Why did this happen?
In this way different colonies of mushroom mycelium or bacteria/mold can temporarily share territory and useful nutrients in the substrate. Since we are dealing with two different microorganisms or different mushroom colonies that compete with each other, usually clear boundaries form between them where they cross aka sectors.
I don't see bacterial or mold contamination so far. Just a struggle between mushroom relatives. As a result we see such immunity reaction of mycelium — metabolites.

On the photo below more intense metabolites. It is a sign of struggling with pathogens (i.e. mild bacterial contamination). Spawn can be used for the next steps of cultivation, but you should check it thoroughly (smell, color) and remove weird areas.

Yellow mycelium as a type of metabolites

Occasionally, snow-white mycelium can turn beige, yellow or even brown during colonisation period in the jar or during fruiting period in the fruiting chamber. It is also a kind of fungal exudate — waste products of mycelium.

This case can be as a reaction of fungal immunity to a minor contamination. It means mycelium struggles successfully! Observe and be attentive.

Minor fungal pigmentation is very common in mushroom growing and nothing to worry about! When mycelium contact and digest other materials from bulk substrate (coco coir, hay, straw, sawdust etc.) it can pick up some amount of matter that change its color. In most cases, yellowish or beige mycelium is not harmful and won't affect its ability to produce healthy mushroom fruit bodies.

Mycelium metabolites or contamination

If mycelium ingests excess of anything that may become toxic enough to eventually harm, disable or kill it, mycelium produces waste exopolysaccharides as antimicrobial agents, acids, excrete enzymes and tries rid itself off that excess.

Metabolites exude is a reaction to stress or response to mild contamination. Mushroom metabolites is a natural mushroom antibiotic and immunity reaction. This means your mycelium is fighting off pathogens or stress. It’s not a contamination itself!

If mushroom mycelium struggles with contaminants, such mushroom cake requires close attention. Very often mycelium copes with mild contamination successfully.

However there are several examples of contaminations are easy to confuse with metabolites. What are they?

Bacterial contamination

It is easy to identify bacterial contamination in mushroom cake by slimy liquid and the specific smell.

Fermented, rotted, cider, sweet and sour, stale, yeasty, smell of dirty socks — those are clear signs of bacterial (also yeast) contamination. Healthy mycelium has an 'earthy' or mushroom smell.

However, it may be hard to feel the smell in a spawn jar/bag. Here is an example with a sign of bacterial contamination in spawn jar:

Wet Bubble disease

Newbie cultivators often confuse secondary metabolites with Wet Bubble disease aka Mycogone.

It seems similar to metabolites, but Mycogone has specific features. An amber liquid with a rotten smell oozes from pins, primordia and clots of mycelium.

Check out full guide: Mycogone contamination aka Wet Bubble disease

Aspergillus yellow mold

Newbie cultivators confuse pigmentation with Aspergillus yellow spp. (Aspergillus flavus). This mold has yellow powder without any liquid on mycelium.