Fishy

Mushrooms that smell of herring

The chemistry behind the fishy smell in mushrooms comes from amine derivatives (for example, trimethylamine), which the mushroom produces as it metabolizes or ages. This smell is most often found in two very particular species, described in detail by Roger Phillips and David Arora:

1. Crab brittlegill (Russula xerampelina): The classic example. A large, handsome brittlegill with a cap ranging from purple to wine red (sometimes olive). Its key feature: as it ages (or when rubbed), the flesh and stem start giving off a distinct, intense smell of herring or crab. Despite the smell, this mushroom is edible and considered one of the tastiest brittlegills. The cut flesh darkens (turns brown), which confirms the identification.

2. Weeping milk cap (Lactarius volemus): A highly prized edible mushroom (in Ukraine it is also called "pidmolochnyk"). It exudes plenty of sweetish white milk, which develops a strong smell of herring or boiled crab in the air.

3. Cucumber cap (Macrocystidia cucumis): A small woodland mushroom that, paradoxically, smells of fresh cucumbers and rotten fish at the same time. It has no culinary value.

A fishy smell as a sign of spoilage

M.Ya. Zerova warns: if the fishy smell comes not from that particular brittlegill or milk cap but, say, from an old porcini or Agaricus, it means only one thing — bacterial rot. The breakdown of proteins (forming those same amines) in old mushrooms produces a persistent smell of rotten fish. Such mushrooms are deadly dangerous because of cadaveric poison.