Studying Mushrooms > Testing Chemical Reactions


Testing Chemical Reactions

by Michael Kuo

How a mushroom's surfaces, flesh, and spores react to the application of certain chemicals can be important information in the identification process. In some cases, nearly identical mushrooms can be easily differentiated by simply applying a drop of common household ammonia to the cap!

It is important to test for chemical reactions on fresh mushrooms, preferably within an hour of picking them. This is not always possible, unless you are willing to carry chemicals with you when you're collecting. But try to test mushrooms as soon as possible when you get home, remembering that the longer you wait, the less reliable your results may be.

Below are details on three chemicals commonly used by mycologists to identify mushrooms, as well as commentary on chemical testing.

Ammonia (NH4OH, Ammonium Hydroxide)

Common household ammonia, available in any grocery store, works perfectly well.

Ammonia is primarily used in the identification of boletes. Place a drop of ammonia on a fresh bolete's cap, stem, sliced flesh, and pore surface. Note any color changes that take place. Some species, like Boletus illudens, will demonstrate a quick flash of one color (for example, blue-green), then settle into another, more permanent color change (for example, grayish). Other species, like Boletus separans, may demonstrate a single color change.

KOH (Potassium Hydroxide)

A 3-5 percent aqueous solution is used to test for color changes. Consult your pharmacist for help in obtaining this chemical, or ask the mycologist at a local university (be nice!)--or purchase KOH online at a scientific equipment site like Fisher Scientific (though you may have some difficulty with this post-911).

KOH is used in the identification of many mushrooms, including boletes, polypores, and gilled mushrooms. For boletes, place a drop of KOH on the cap, stem, sliced flesh, and pore surface. For polypores, apply the KOH to the flesh and the cap surface. For gilled mushrooms, place a drop on the cap surface. Note any color changes that take place. A change to yellow is sometimes found in species of Agaricus and Amanita; magenta or olive reactions can help identify species of Russula and Lactarius; deep red or black reactions can help sort out many gilled mushrooms; black reactions among polypores are crucial separators; and various colors are produced with boletes. Don't forget that a "negative" reaction (no color change) may also be an informative character!

I have heard that liquid Drano may (may) work as a substitute for KOH; I have not experimented.

Iron Salts (FeSO4)

A 10 percent aqueous solution is used to test for color changes. As with KOH, you will need to consult your pharmacist for help in obtaining this chemical, or ask the mycologist at a local university--or purchase FeSO4 online at a scientific equipment site like Fisher Scientific (though you may have some difficulty with this post-911).

FeSO4 is used primarily in the identification of boletes and russulas. For boletes, place a drop on the cap, stem, sliced flesh, and pore surface; for russulas, place a drop on the stem surface.


Mycologists have not tried applying these chemicals to every mushroom. You may discover interesting things by simply dropping these chemicals on mushrooms you collect. This kind of experimentation has led me to discover: that eastern North America's chanterelles do not react to iron salts with the exception of one species (Cantharellus appalachiensis) which is frequently hard to separate from other chanterelles on the basis of its physical appearance (see Reactions to Iron Salts among the Chanterelles); that Rhodotus palmatus displays a striking green reaction to iron salts; that ammonia, KOH, and iron salts are absolutely useless in sorting out morel species defined by DNA (or any other means); and a few other things that I will remain silent about for now since I want to double- and triple-check results.

Bolete Frustration

While chemical testing is invaluable to the identification of boletes, you will soon find that reactions to chemicals are inconsistently recorded in the literature. It would be nice if nine reactions were recorded for each bolete: ammonia on the cap, flesh, and pore surface; KOH on these three surfaces; and iron salts. Unfortunately, things aren't that nice. Some mushrooms have been tested by publishing mycologists with ammonia only, others with KOH only, and so on . . . and there are plenty that haven't been tested and documented at all.

To add to the problem, some mycologists disagree with others on the validity of their tests. Though this comes as no surprise to anyone familiar with the academic world, it is more than a little frustrating to know that one prominent bolete authority feels that another prominent bolete authority's chemical tests are invalid because they were not performed on fresh mushrooms.

Melzer's Reagent and Iodine

The material about Melzer's reagent and iodine reactions previously included on this page has been moved; see Using a Microscope: Equipment for details about Melzer's reagent and how to obtain it; see Using a Microscope: Viewing and Measuring Spores for definitions of "amyloid," "dextrinoid," and "inamyloid" reactions to Melzer's. For details on using simple tincture of iodine as a substitute for Melzer's (not always successful), see:

Leonard, Lawrence M. (2006). Melzer's, Lugol's, or iodine for identification of white-spored Agaricales. McIlvainea 16.

Links from other pages at this site have been adjusted, but I am placing this note here to accommodate bookmarks and links from elsewhere.


Hapalopilus nidulans
KOH on Hapalopilus nidulans

Russula flavida
KOH on Russula flavida

Rhodotus palmatus
Iron salts on Rhodotus palmatus

Agaricus leptocaulis
KOH on Agaricus leptocaulis

Cortinarius croceus
KOH on Cortinarius croceus

Bothia castanella
Chemicals on Bothia castanella

Cantharellus appalachiensis
Iron salts on Cantharellus appalachiensis

Boletus separans
Ammonia on Boletus separans

Clavariadelphus unicolor
KOH on Clavariadelphus unicolor

Click the image below for a movie of the cap reaction to ammonia in Boletus pseudosensibilis.

Boletus pseudosensibilis
(WMV file - 410KB)

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Cite this page as:

Kuo, M. (2006, November). Testing chemical reactions. Retrieved from the MushroomExpert.Com Web site: