Blackening

Hazel boletes, birch boletes and melanin

In the "Key to the Fungi of Ukraine," M.Ya. Zerova notes darkening all the way to black as the main distinguishing feature of the genus Leccinum (birch boletes, orange boletes, hazel boletes).

The chemistry of this blackening is well understood. The flesh of these mushrooms is rich in the amino acid tyrosine. On contact with air (a cut) or under heat (cooking), enzymes oxidize the tyrosine, and a chain of chemical reactions produces the pigment melanin — the same pigment responsible for the black color of human skin or hair.

Roger Phillips gives the most striking examples:

1. Hazel bolete (Leccinum carpini): Its flesh is the record-holder for color change. Cut this mushroom and it first turns pink, then lilac-gray, and within 10-15 minutes takes on a deep, almost black color.

2. Red-capped scaber stalk / orange birch bolete (Leccinum aurantiacum): The thick stem of this mushroom darkens quickly when cut, passing through stages from pink to dark purple and black.

David Arora describes another remarkable gilled mushroom for which blackening is the main diagnostic feature — the blackening brittlegill (Russula nigricans). It's a large, firm mushroom whose damaged flesh first turns red and then becomes completely and irreversibly charcoal black (and stays that way, even as a dried-up mummy in the forest, until the next spring).

What blackening means in the kitchen

Blackening flesh has nothing whatsoever to do with toxicity. Melanin is completely safe for human health.

The black color does, however, have a big effect on how dishes look:

- Soup made from hazel boletes or birch boletes will always be dark and cloudy.

- Fried mushrooms will take on a charcoal tint.