Identifying Mushrooms Through Bruising and Bleeding

Of the fungus, that is. Not yourself!

Another feature to consider when identifying mushrooms is whether there is bruising or bleeding when they’re cut.

Certain mushrooms will change colors when damaged or injured. Cutting into a mushroom and observing any color changes can be very important when trying to determine what it is.

A bolete bruising blue — This bolete stains blue when bruised.

Please note that color change alone is one of the least reliable ways to go about mushroom identification. There are always variations, and color changes may not be trustworthy depending on the age of your fungus. Use mushroom bruising as just another tool in your identification arsenal.

Let’s examine identifying mushrooms through bruising and then through bleeding. We’ll end with a quick list of some well-known examples. For more mushroom identification features, see this page.

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Mushroom Bruising and Staining
Steps For Analyzing Bruising and Staining Mushrooms
Mushroom Bleeding
Identifying Mushrooms: Bruising and Bleeding Examples

Mushroom Bruising and Staining

While identifying mushrooms, check for bruising by nicking the top and bottom of the cap and watching for any color change. Try this within 30 minutes of picking, as specimens that are not fresh won’t give a reliable result.

Note the blue coloring when the cap is sliced — on this bolete species the flesh slowly turns blue.

bolete turning blue when cut in half — Bolete turning blue when cut in half.

Why does this happen? The color change is caused by a chemical reaction that occurs when certain compounds in the cell walls of the mushroom are exposed to air.

Once you nick the cap and break the cell walls, oxygen in the air mingles with these compounds and changes them. Take Gyroporus cyanescens for example. When exposed to air, the variegatic acid in this mushroom is converted to the blue-colored molecule quinone methide.

bolete staining dark blue when cut — The (L) bolete stains dark blue almost black while the (R) bolete is lighter blue with some reddish tints.

bolete staining light blue when cut — The (L) bolete stains dark blue almost black while the (R) bolete is lighter blue with some reddish tints.

There are many famous blue-bruising mushrooms. A common rule for boletes is that you shouldn’t eat one that has a red pore surface and bruises blue. Because so many blue bruising boletes are poisonous, it’s best to avoid them altogether.

Steps For Analyzing Bruising and Staining Mushrooms

Time how long it takes to stain — some are very slow and can take up to an hour. Most identification guides use 5 minutes as the marker. It either turns color in less than five minutes, more than five minutes, or doesn’t change color at all.
Notice the exact coloring — is it dark blue, blue/green, red, pinkish, or brown? It makes a difference for identification.
Is the the stem, cap, gills, or pores that stain? Some mushroom gills stain but their stems and caps don’t.

bolete with dark blue bruising — The spores and stem turn deep blue/black when cut.

Some people think that all blue bruising mushrooms are safe to eat or are hallucinogenic. The bolete rule above proves that is not true. This myth is an example of why identifying mushrooms through bruising alone is a bad idea!

examples of bruising and bleeding — Saffron milky caps on the left, bruise green when handled. Bolete on right turns blue when sliced in half.

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Mushroom Bleeding

Certain mushrooms will exude a milky liquid substance when they are cut. This is not real “blood” of course but natural latex that’s produced when the mushroom is injured.

Milky cap bleeding white latex. — A milky cap with white droplets of milky latex when the gills are cut or damaged.

The exact reason for the latex is not fully understood. It is believed to be a method of defense, due to its bitter taste and the fact that it dries to form a protective coating around the injury. This keeps out bacteria and other contaminants.

Some of the most famous bleeding mushrooms are those in the Lactarius genus. These are called the milky caps due to the milky latex they exude upon injury.

Bleeding tooth fungus on left bleeds red; milky cap on right bleeds white.

If you’re observing any bleeding during mushroom identification, be sure to note both the initial liquid color and the final dried color. These will sometimes be different.

An example is the green bruising and orange bleeding Lactarius deliciosus, the saffron milk cap. When bruised, the mushroom turns green. However, when the gills are cut, this mushroom bleeds orange and it doesn’t change color.

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Identifying Mushrooms: Bruising and Bleeding Examples

Below are some examples of bruisin’ and bleedin’ mushrooms. This list is by no means exhaustive:

Agaricus bisporus (white button mushroom) – Usually bruises pinkish. Stick your thumb into a grocery store-bought one to test.
Boletus campestris – Bruises blue or blue-green. Many yellow-pored boletes bruise blue.
Psilocybe cubensis – The stems bruise blue or blue-green. This is a hallucinogenic mushroom, but note that not all hallucinogenic mushrooms bruise blue.
Russula rubescens – Bruises reddish, and then slowly turns to black.
Mycena haematopus – Bleeds purplish.
Lactarius helvus (maple syrup milky cap) – Bleeds colorless latex that smells like maple syrup.
Lactarius chrysorrheus – Bleeds white latex that dries to a deeper yellow.

So the next time you’re identifying mushrooms, don’t forget to check for bruising and/or bleeding. While no identification is guaranteed, it can be an important piece of information!