When certain mushrooms are cut or bruised, their flesh can undergo a noticeable color change, often turning red. The visual transformation, which can range from subtle pink to deep crimson, is a distinct characteristic of particular mushroom species. This article examines the scientific basis for this reddening, identifies common mushroom varieties that display it, and discusses important safety considerations.
The Biological Basis of Reddening
The color change observed in certain mushrooms when their tissue is damaged is primarily due to enzymatic reactions. When the mushroom’s cellular structure is disrupted, compounds within its cells are exposed to oxygen, triggering an oxidation process. The enzymes involved, predominantly tyrosinases (also known as polyphenol oxidases), catalyze the oxidation of specific colorless or lightly colored compounds present in the mushroom’s flesh, such as phenolic compounds or certain psilocybin derivatives.
Tyrosinases are copper-containing enzymes widely distributed in fungi. They facilitate two main reactions: the hydroxylation of monophenols to o-diphenols and the subsequent oxidation of these o-diphenols to o-quinones. These o-quinones are highly reactive and can then undergo further non-enzymatic reactions, including polymerization, to form colored pigments. These pigments often manifest as red or reddish-brown compounds, which are a form of melanin or related products. The speed and intensity of the color change can vary depending on the specific mushroom species, the concentration of the reacting compounds, and environmental factors like pH and temperature.
Common Mushrooms Exhibiting This Trait
Many mushroom species exhibit a reddening reaction when their flesh is cut or bruised, providing a distinctive identification feature. Among the boletes, a group of mushrooms characterized by pores instead of gills, several species are known for this trait. For instance, Neoboletus luridiformis, often called the scarletina bolete, has flesh that turns rapidly blue-black upon damage, and its stem can show red coloration that deepens when cut. Another example is Boletus erythropus, also known as the dotted-stem bolete, whose yellow flesh quickly changes to an intense blue upon cutting, with some red tones in the stem base. Its pores are typically red and also blue when bruised.
The genus Lactarius, commonly known as milk-caps, includes species that exude a colored latex when injured, with some producing red liquid. Lactarius sanguifluus, the bloody milk cap, releases a blood-red to purple latex when cut or bruised. Its cap is orangish to reddish-brown, and the gills are pinkish to purplish. Lactarius semisanguifluus produces an orange latex that turns wine-red within minutes.
Some Russula species also display reddening when damaged. The “blushing and blackening” russulas, such as Russula nigricans, will bruise or slice to a reddish color that then progresses to gray or black. The gills of Russula nigricans are initially cream-colored but slowly stain red before turning dark gray to black with age and damage. Additionally, some Agaricus species, such as Agaricus sylvaticus (blushing wood mushroom), are known for their flesh turning bright red when scratched or broken, a characteristic that helps distinguish them from yellow-staining Agaricus species.
Edibility and Safety Considerations
The reddening reaction in a mushroom’s flesh does not reliably indicate whether it is edible or toxic. For example, some boletes that turn blue or red upon bruising are edible when cooked, but others are toxic. Relying solely on a color change for identification can lead to dangerous misidentification.
Consuming any wild mushroom requires positive, expert identification, and foraging without sufficient knowledge of local species carries significant risks. Even experienced foragers exercise extreme caution, adhering to the principle of “when in doubt, throw it out.” A mushroom’s appearance, including its color change upon injury, is just one of many features that mycologists use for identification. Other important characteristics include spore print color, habitat, smell, cap shape, gill attachment, and the presence or absence of a ring or volva. Always consult field guides, expert mycologists, or local foraging groups for accurate identification before consumption.