The Leathers Edibility Test

I have spoken several times about the edibility test advocated by Dr. Chester Leathers, who is the president of the Arizona Mushroom Club and an emeritus professor of mycology at Arizona State University. Since this is always explained when the Club meets for its forays, I assumed everyone knew what was being discussed. But as we are now seeing hundreds of hits on this site per day from all over the world, I wanted to write down an exact protocol to follow so everyone knows what we are talking about.

The first thing to note is that this is absolutely NOT a way for you to go around testing random unknown mushrooms to see if they are safe. Even a single bite of a Death Cap (Amanita phalloides) or Destroying Angel (A. ocreata) might be enough to kill a person. Instead, this method is used once you have reliably identified a mushroom as to genus and species, in order to ensure that eating it agrees with you. This is necessary because many people may be sensitive or allergic to mushroom species that are generally considered edible– even the store-bought white button mushroom, Agaricus bisporus!

The other main point to remember is that this test establishes whether or not a given species is edible for YOU as an individual. It does not prove the mushroom to be innocuous for your wife, kids, or dinner-party guests. Each individual in your household consuming a particular species of wild-foraged mushroom needs to perform this test to establish its edibility for themselves.

Shrimp Russulas in the skilletOnce you have decided that it is safe to attempt consumption of the particular type of mushroom you have located, you’ll want to prepare it for eating.  For this purpose, it’s sufficient to sauté your mushroom in a skillet with a bit of butter or olive oil.  Wild mushrooms should be well cooked, with very few exceptions, so give it a good 7-10 minutes over medium heat.

To begin, take a single piece that fits in a teaspoon.  Chew it up and spit it out. If you are susceptible to having a true allergic (as opposed to toxic) reaction, this will typically occur in the first hour or so.

If there is no immediate allergic reaction, you can now entirely consume a single piece of the same size. However, after doing so, you must now wait eight hours before continuing. This long delay is recommended because some of the most dangerous and deadly poisonous species have a latent period that is typically 6 to 8 hours before a delayed reaction occurs.

In some cases, a knowledgeable collector may be testing a well-recognized genus such as Leccinum, Agaricus, or Russula that contains “vomiter” or “sickener” members capable of causing short-onset gastrointestinal upset, but has no deadly poisonous species in North America.  In this circumstance some people will shorten the testing period to 3-6 hours, but this is not generally recommended, and certainly not when there is any possibility of confusing your specimen with a deadly Amanita, Galerina, Lepiota, or Cortinarius.

After these first two tests, if you have not noticed any gastrointestinal distress, rash, soft tissue swelling, wheezing, shortness of breath, visual changes, or other unusual symptoms, you may now take two teaspoons’ worth.  Again, wait eight hours.

Now, if there are once again no symptoms, you may try a heaping tablespoon full of your mushroom.  As before, wait eight more hours after eating.

Assuming no symptoms, do likewise with two tablespoons, then a handful, and then two handfuls, waiting eight hours between each test.

Once you have eaten a two-handful serving with no untoward effects, you may assume that this particular species is safe for you to eat ad lib.  This will take several days, but the rewards will last for a lifetime of safe mushroom collecting and consumption.

As always, When in doubt, throw it out!

About Christopher May

Chris is a radiologist in private practice in Scottsdale. He is married to Barbara May, with two grown children, Megan and Nick.
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