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Smell

Sour

Sour — mushrooms with the trait «Sour»

A smell of acid, vinegar or sour milk always makes a forager suspicious. In the mushroom kingdom, a sour smell can mean two completely different things: either it is a natural genetic trait of a particular species, or it is a warning that the mushroom is unsafe to eat.

2 species in the database.

A natural sour smell

M.Ya. Zerova notes in her "Key to the Fungi of Ukraine" that some genera of macromycetes have a faint, slightly sour aroma as their physiological norm. Most often this applies to the brittlegill family (Russulaceae), namely the milk cap genus (Lactarius).

David Arora describes this smell in more detail in "Mushrooms Demystified":

- Many milk caps exude a white milky latex that, when exposed to air, can take on a faint smell of sour milk or a fruity tang.

- The beefsteak fungus (Fistulina hepatica), which grows on old oaks, often has not only a sour taste thanks to its high ascorbic acid (vitamin C) content, but also a faint, slightly sour aroma.

A sour smell as a sign of spoilage

However, Roger Phillips warns: in 90% of cases when you find a bolete (porcini, slippery jack or birch bolete) or an Agaricus mushroom that reeks sharply of acid, it is a sign of bacterial rot.

Mushroom fruiting bodies are made of protein and water. With warmth and moisture, bacteria multiply in them quickly (just like in a forgotten piece of meat). As they live, these bacteria release acids (butyric and acetic in particular), which creates a sharp sour and later a putrid smell. Old, overripe mushrooms with a soft, spongy "sponge" under the cap almost always start to smell sour.

Questions and answers

If a porcini smells sour, can you eat it after boiling?
Absolutely not. A sour smell in a bolete means bacterial breakdown of proteins is already underway. Even long boiling will kill the bacteria, but it will not neutralize their toxins (ptomaines). Eating such a mushroom will lead to severe food poisoning.
How can you tell a natural sour smell from the smell of a spoiled mushroom?
A natural slightly sour smell (for example, in some milk caps) is faint, fresh and often comes with fruity notes. The smell of spoilage is sharp, unpleasant, vinegary or reminiscent of soured cabbage soup, and it always comes with a change in the mushroom's texture (the mushroom becomes limp, dark, slimy or too soft).
Why can picked mushrooms go sour in a bag?
Never collect mushrooms in plastic bags! Mushrooms "breathe," giving off moisture and heat. In a closed bag with no airflow, a greenhouse effect builds up, triggering an instant explosion of bacterial growth. Even fresh, firm mushrooms in a bag can go sour and become dangerous to your health in just 2-3 hours. Collect mushrooms only in well-ventilated baskets.

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