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Flesh color change

Yellowing

Turns yellow — mushrooms with the trait «Turns yellow»

Mushroom flesh turning yellow when cut or when you press the cap is a relatively rare feature in the world of mycology. Yet for one particular group of mushrooms (namely Agaricus) it is the single most important danger warning.

24 species in the database.

Yellowing in Agaricus

In "Mushrooms Demystified," David Arora divides wild Agaricus into two groups by how they react to damage: those that redden and those that yellow. The yellowing group is the trickiest, since it contains both the finest delicacies and toxic species.

Roger Phillips stresses a fundamental difference in the nature of the yellowing:

1. Poisonous (rapid) yellowing:

The emblem of this group is the yellow stainer (Agaricus xanthodermus). If you cut through the base of its stem (the bulb) or scratch the cap hard with a fingernail, the flesh instantly turns a bright chrome or canary yellow. This lightning-fast reaction comes with a sharp, unpleasant smell of phenol (like a pharmacy or ink). These mushrooms are poisonous and cause severe stomach upsets.

2. Edible (slow) yellowing:

Some first-rate woodland species, such as the wood mushroom (Agaricus silvicola) and the prince (Agaricus augustus), also turn yellow. But their reaction is quite different: the cap or stem stains yellowish or ochre when touched, very slowly and dully. What's more, they have a wonderful sweet smell of almond or anise.

Yellowing in boletes

M.Ya. Zerova notes that yellowing also occurs among some pored mushrooms of the family Boletaceae. For example, in the saffron bolete (Leccinum crocipodium), the white flesh may first turn saffron yellow when cut, then redden and finally blacken. This is a perfectly normal process for this edible mushroom. Some Xerocomus species may also show a slight yellowing before turning blue.

Questions and answers

If an Agaricus has turned yellow but doesn't smell of phenol, can you eat it?
Be careful. In cold or very wet weather, the poisonous yellow stainer (Agaricus xanthodermus) may barely smell at all. Try putting a piece of the yellow flesh on a hot frying pan: if a sharp chemical smell appears, the mushroom is poisonous.
Why don't white supermarket mushrooms turn yellow?
The store-bought button mushroom (Agaricus bisporus) belongs to a different section of the genus. Its flesh may only turn slightly pink or stay white in the air or when pressed. It never turns bright yellow.
Are there amanitas that turn yellow when cut?
Most amanitas (including the deadly death cap) don't change the color of their flesh. The absence of yellowing or reddening is one of their characteristic features (their flesh always stays white).

Sources

  1. 1.Зерова М.Я. та ін. Визначник грибів України. 1979
  2. 2.Roger Phillips. Mushrooms (Roger Phillips)
  3. 3.David Arora. Mushrooms Demystified
  4. 4.Index Fungorum