How Mushrooms Turn Blue: The Science Behind It

Mushrooms are fungi that produce psychotropic compounds, which can cause hallucinations and alter human perception. Some mushrooms, such as those from the Psilocybe genus, instantly develop a blue coloration when they are cut or bruised. This phenomenon, known as bluing, has puzzled scientists for decades. Recently, researchers have made significant progress in understanding the chemical reactions that lead to this colour change. German researcher Dirk Hoffmeister and his team identified the source of the bluing reaction in psychoactive mushrooms, involving the activation of two enzymes, PsiP and PsiL, which convert psilocybin to psilocin. These enzymes are similar to those in the human liver that catalyse psilocybin to psilocin, resulting in a psychedelic experience. While the mystery of why magic mushrooms turn blue when damaged has been largely unravelled, further research is likely ongoing to fully comprehend the complex nature of these colourful fungi.

Why do magic mushrooms turn blue?

Magic mushrooms, or Psilocybe, are fungi that produce the psychotropic compounds psilocybin and psilocin. They are psychedelic drugs, which means they can affect all the senses, altering a person’s thinking, sense of time, and emotions. They are also hallucinogenic and can cause a person to see or hear things that do not exist or are distorted.

Magic mushrooms are one of several species that instantly develop a blue coloration when they are cut or bruised. This phenomenon has puzzled scientists for decades. The mechanism that underlies this ‘bluing’ is well known for some mushrooms, but not for psychedelic mushrooms that contain psilocybin.

Recently, chemists have unraveled this mystery, revealing that the dark blue pigments are similar to indigo, the dye used to produce blue jeans. The pigment is not just a single compound but a complex mixture of linked psilocybin oxidation products. All of the six mushroom pigments identified are products of a cascade reaction starting with psilocybin. A phosphatase enzyme takes off its phosphate group, converting it into psilocin. An oxidizing laccase then creates psilocyl radicals, which combine to form C-5 coupled subunits and then further polymerize via C-7.

Scientists have also isolated two enzymes that give psilocybin-laden mushrooms their blue color. It has been hypothesized that the blue pigments might serve a protective role, acting as an on-demand repellent against predators. The compounds might produce reactive oxygen species, which are toxic to any insect nibbling on the mushrooms.

The chemical reaction behind the blue colour

The blue colour of some mushrooms has puzzled scientists for decades. However, recent research has revealed that the phenomenon is caused by a complex mixture of linked psilocybin oxidation products.

Psilocybin is a psychotropic compound found in certain types of fungi, specifically the genus Psilocybe, which includes Psilocybe cubensis and Psilocybe azurescens. When these mushrooms are cut, bruised, or damaged, they instantly develop a dark blue colour at the site of injury. This colour change is known as "bluing" and is a result of the oxidation of psilocybin.

The oxidative coupling of psilocyl residues occurs primarily via C-5, as indicated by in situ 13C NMR spectroscopy. MS and IR spectroscopy further revealed the formation of a heterogeneous mixture of psilocyl 3- to 13-mers, suggesting multiple oligomerization routes depending on oxidative power and substrate concentration. The blue pigments produced are not a single compound but a complex mixture of linked psilocybin oxidation products, most of which are quinoid psilocyl oligomers. These oligomers share structural similarities with indigo, a deep blue pigment used in dyeing jeans.

While the chemical reaction behind the blue colour has been elucidated, the exact function of these pigments remains a mystery. One hypothesis suggests that the blue compounds may serve a protective role, acting as a repellent against insects or other predators.

Different types of blue-bruising mushrooms

Mushrooms that bruise blue include the Boletus campestris, Psilocybe cubensis, and several other yellow-pored boletes. These mushrooms are commonly known as "magic mushrooms" due to their psychedelic properties. They contain the psychotropic compounds psilocybin and psilocin, which are responsible for the hallucinogenic effects experienced by consumers.

The blue bruising in Psilocybe mushrooms results from a complex mixture of linked psilocybin oxidation products. Most of these compounds are quinoid psilocyl oligomers, structurally similar to indigo, the dye used for blue jeans. The oxidation of psilocybin by an enzyme creates psilocyl radicals, which combine to form subunits that further polymerize, resulting in the blue coloration.

While the exact purpose of the blue pigments remains unclear, one hypothesis suggests they may serve a protective role. The compounds could produce reactive oxygen species, which would be toxic to insects attempting to feed on the mushrooms.

It is important to distinguish blue bruising from blackening in mushrooms. Heavy blue bruising may appear black, but if the mushrooms develop black spots with an unpleasant smell, it indicates mould or rot, rendering them unsafe for consumption.

In addition to the blue-bruising varieties, some mushrooms exhibit other colour changes when bruised or cut. For example, the Agaricus bisporus (white button mushroom) typically bruises pinkish, while the Russula rubescens bruises reddish before slowly turning black.

Are blue-bruising mushrooms always psychoactive?

Blue-bruising mushrooms are not always psychoactive. While some blue-bruising mushrooms are indeed psychoactive, such as Psilocybe azurescens, not all blue-bruising mushrooms contain the psychoactive compounds psilocybin and psilocin. In fact, several non-psychoactive strains of mushrooms are known to develop blue bruises. However, it is believed that the bluing reaction in these mushrooms is somewhat different, leading to different shades of blue and produced by different compounds than those found in psychoactive mushrooms.

The blue colour in mushrooms is caused by a complex mixture of linked psilocybin oxidation products, which are similar to indigo, the dye used to produce blue jeans. This colour change occurs when mushrooms are cut or bruised, and it is well known for some mushrooms, but the mechanism underlying this "bluing" puzzled scientists for decades.

The blue pigments' function remains a mystery. However, it has been hypothesised that it might serve a protective role, acting as an on-demand repellent against predators. These compounds may produce reactive oxygen species, which are toxic to insects that nibble on the mushrooms.

While blue bruising is a common way to identify mushrooms, it is not always reliable. It is important to use other identification methods as well, as not all blue-bruising mushrooms are safe to consume. For example, a common rule for boletes is to avoid consuming those with red pore surfaces that bruise blue, as many of these are toxic.

How to identify blue-bruising mushrooms

While identifying mushrooms, check for bruising by nicking the top and bottom of the cap and observing any colour change. This process of bruising is also known as "bluing". It is believed that bluing occurs due to the decomposition of some of the psychoactive compounds in magic mushrooms. Bluing is incredibly common and has been discussed extensively, however, it is still unclear why this happens. It is widely believed that bluing occurs due to the degradation of psilocin by enzymes within the mushroom's cells in response to oxidation.

Some species of mushrooms that have been confirmed to contain psilocybin do not bruise at all, hence, not all magic mushrooms will experience bruising. Bluing should not be confused with blackening, as heavy blue bruising can sometimes appear black. If mushrooms develop black spots that smell unpleasant, this is a sign of mould or rot, indicating that they may no longer be safe for consumption.

To identify blue-bruising mushrooms, it is important to note the exact colour and the part of the mushroom that stains. Observe whether it is the stem, cap, gills, or pores that are staining. Some mushroom gills stain, but their stems and caps do not. Timing how long it takes for the mushroom to stain is also important, as some mushrooms take longer than others. Most identification guides use 5 minutes as the marker.

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

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