On Eating Raw Mushrooms

© David Campbell

Original publication: Mycena News, November 2008

There seems to be an ongoing temptation amongst mycophagists and chefs to serve mushrooms raw or barely cooked. Generally speaking, this is not the best of ideas.

The mycochitin composition of mushroom cell walls, as opposed to cellulose walls of plant cells, is difficult for humans to digest. Our stomachs resent indigestible items, and often forcibly reject them without further ado. The cooking process helps break down fungal cell walls, rendering mushroom flesh not only more readily digestible, but also releasing significant nutritional value contained within the cells.

Further, many mushrooms considered edible contain irritating or toxic components readily destroyed or eliminated by cooking. Therefore, common and valid mycophagal wisdom dictates that all edible mushrooms should be cooked prior to consumption. Exceptions are made only if one has specific knowledge that a particular pristine species is safe to eat raw. With these few au naturel exceptions, the “pristine” part becomes especially important. Environmental or microbial contaminations to the mushroom flesh may pose potential health hazards. By dramatic example, a few free-spirited youths in Hawaii a few years ago blithely consumed blue-staining Psilocybes as they went collecting from cow patties. What a downer it must have been a short while later, when the doctor told them they had nematodes!

Bear in mind, there is much yet to be learned about eating mushrooms; wild or tame, cooked or raw…the research is in progress, and we the mycophagists are, by default, the guinea pigs. What we know of mushroom edibility is primarily the result of shared anecdotal information, as compiled and recorded over the course of human history. Hardly do we rest on hard science or a complete body of knowledge when we decide whether or not to eat a given fungus. In fact, another good general reason for cooking one’s mushrooms is the blind stab it represents at protecting us from the unknown.

The list of edible mushrooms considered safe for raw consumption is quite short. Even species commonly eaten raw, especially the ubiquitous button mushroom, Agaricus bisporus, have their drawbacks. Buttons, and many other edible mushrooms contain various hydrazines, a group of chemical compounds generally considered carcinogenic. For the most part, these compounds are heat sensitive, readily volatilized and expunged from the fungal flesh by proper cooking. This basic understanding is employed by some more adventurous mycophagists to justify eating the false morel, Gyromitra esculenta, a deadly poisonous mushroom according to every published description I’ve read. Those who so indulge in this species believe the hydrazine compounds present (naturally occurring gyromitrin converts to monomethylhydrazine, or MMH when heated) to be effectively removed, at least to a large degree, by thorough cooking, provided one stands well clear of the fumes during the cooking process. The more conservative mycophagists consider this practice questionable, at best, and argue that gyromitrin is never completely eliminated, that there may well be harmful cumulative factors associated with repeat false morel consumption….I say, “To each his own,” in decisions such as this, cautioning only that the innocent and unaware should never be arbitrarily included in mycophagal experimentation.

The kicker with Agaricus species, including the buttons, is that one of their primary hydrazine components, along with gyromitrin, is “agaritine,” a substance somewhat resistant to cooking heat, with a significant percentage (25–75%) of agaratine material typically remaining after being subjected to various methods of cooking. So, the question as far as avoiding hydrazines in Agaricus is concerned, actually becomes whether to eat members of this genus at all.

We need to keep in mind that lab tests and subsequent conclusions drawn concerning carcinogenic or mutagenic health hazards of hydrazine involve massive doses of isolated extracts administered to mice in a concentrated time frame. Similarly disturbing test results are likely to be found with many substances present in many, many foods humans commonly eat without suffering or even worrying about any particular health concern. The relatively unblemished human history of consuming edible Agaricus species suggests we may continue to do so. The science may suggest we should not over indulge, but we already knew that. As I know of no one stricken by cancer or any other malady as particular result of eating Agaricus, and since the genus includes some of the most delectable of all edibles, there are several wild Agaricus species that remain firmly ensconced on my preferred edibles list.

Unfortunately, the button mushroom industry routinely promotes the use of their product raw, especially on salads, perpetuating the myth that mushrooms need not be cooked. I presume such promotion to be a profit driven policy. A recent Poison Control Center response incident with Gyromitra montana purchased at a Whole Foods store demonstrated the broader danger of public misconception about the safety of eating store-bought mushrooms raw. The blithe and unwitting “victim” reportedly took a nice chomp from her just purchased bull’s nose as she walked out of the store! As far as I know, this mushroom contains hydrazine compounds that may be quite similar to those found in Gyromitra esculenta, but in sufficiently reduced concentrations to be listed in many published mushroom guides as edible, if cooked. In this case, the immediate effects induced by consumption of the raw Gyromitra flesh easily trumped any long-term health concerns.

Cooking of mushrooms generally reduces the likelihood of gastro-intestinal irritation, and allergenic reaction. Popular comestibles such as morels (Morchella sp.), hedgehogs (Hydnum repandum) and oyster mushrooms (Pleurotus sp.) will almost certainly make one ill if eaten raw. Chanterelles (Cantharellus cibarius, C. formosus, etc.) are generally considered stomach irritants in the raw. King boletes (Boletus edulis) are known to cause many people gastro disturbance even when cooked, but are nonetheless popular raw in the hard-button stage. Diners served a raw porcini salad are well advised to eat just a tat…or else.

Some small and/or gooey mushrooms are often eaten raw, mostly because they hardly lend themselves to cooking. The witch’s butters (Tremella mesenterica, T. foliacea, Dacromyces palmatus) and toothed jellies (Pseudohydnum gelatinosum, Phlogiotis hellvelloides) are good examples of fungi commonly eaten “as is,” sans ill reported effect, or at least I’ve heard no dire reports. Part of the safety in occasionally consuming oddball species such as these is we never really eat all that much. In fact, the key to safe consumption of any and all mushrooms, aside from proper ID and sufficient cooking, is moderation.

Somewhat ironically, given the nefarious reputation of the genus at large, the most readily digestible, or at least most innocuous, mushroom to eat raw, by my experience, is the coccoli (Amanita lanei). I generally eat these mushrooms raw because they so remind me of oysters (mollusks, not the fungus), in that the more you cook them, the less desirable they become. In all fairness, I should mention that I do chemically cook my coccoli salad with lemon juice marinade…I have never suffered any discomfort, nor have I heard complaints from those who have consumed my “coccoli ceviche.” Of course, you are not likely to see edible Amanita specimens for sale in the market, nor should you, methinks. Our markets and the public both lack the knowledge and sophistication to safely trade a product so easily confused with its lethal cousins!

Other methods of chemical cooking, aside from citric acid, involve brining or pickling. I lack personal experience with this form of mushroom processing, but I have heard and read it is used to apparently satisfactory effect in many cultures, notably Russia, where many kinds of freshly collected Russula and Lactarius species are reportedly tossed collectively into the brine barrel, to be directly retrieved and munched later. Of interest with this method is that some of these species so prepared are considered poisonous when cooked by conventional heat application.

As stated above, cooking with heat destroys many toxins and irritants found in mushrooms. Toxins present in various redsponged species of the genus Boletus, for instance, may allegedly be neutralized with prolonged cooking. Ibotenic acid and related toxic compounds present in Amanita muscaria are not heat-sensitive, but are soluble in boiling water. This mushroom may be rendered edible by properly leaching the mushroom toxins into boiling water, tossing the water, and eating what’s left of the mushroom. I have been party to this process several times while participating in David Arora’s annual Mendocino seminars, where we often served properly processed fly agaric, sliced and boiled, to the assembled throng, free from toxic effect.

Make no mistake, however. Deadly amanitin toxins present in the death cap and destroying angel (Amanita phalloides, A. ocreata, etc.) are oblivious to heat and leaching processes, retaining their virulent properties regardless of cooking methods applied. Cooking or not makes no difference with these toadstools; they remain fully capable of killing any sad soul who egregiously partakes, regardless.