The current boiling recommendation for handling false morels is not entirely foolproof. According to a report by the Finnish Food Authority’s Risk Assessment Unit, even after boiling the mushrooms twice, nearly one-fifth of the original toxin content remains. The report, based on literature sources, examined Finnish exposure to gyromitrin in false morels, the associated health risks, and compared different processing methods to reduce the mushrooms’ toxicity.
Gyromitrin and its breakdown products found in false morels can cause poisoning, with symptoms such as nausea, vomiting, and diarrhea. In severe cases, gyromitrin can lead to neurological symptoms, liver damage, and even death. While recommended processing can reduce the amount of toxin, no method completely removes all gyromitrin. Even mushrooms treated according to the boiling guidelines still contain residual toxins.
The Risk Assessment Unit estimated Finnish exposure to gyromitrin using data from the total harvest of commercially collected false morels, common recipes, and concentration data compiled from literature. Exposure was calculated for both properly processed and unprocessed mushrooms. In a good false morel season, Finns are estimated to consume up to three million false morel meals.
The harmful effects of gyromitrin have been studied in animal experiments, primarily by determining the dose that kills half of the test animals. However, such results are poorly applicable when trying to determine harmful levels for humans. Additionally, the toxicity of gyromitrin’s breakdown products has only been studied through inhalation exposure, which differs significantly from absorption through the digestive tract. As a result, no safe threshold level for gyromitrin or its toxic metabolites has been established for human consumption.
Animal studies have also shown that gyromitrin and its breakdown products can cause various cancers in test animals. However, due to shortcomings in the experimental setups, these findings cannot be generalized to humans. Current understanding suggests that gyromitrin is not carcinogenic to humans, but this assumption is based more on a lack of data than on definitive proof of safety.
Drying only halved the toxin content
The study also reviewed literature to determine the most effective method (boiling, double boiling, or drying) for reducing the toxicity of false morels. According to current guidelines, false morels should be boiled twice in plenty of water (one part mushrooms to three parts water) for five minutes each time.
Double boiling proved to be the most effective method for removing the toxin. However, even then, about 18% of the original toxin content remained in the mushrooms on average. Drying was less effective, with up to half of the toxin potentially remaining in the mushrooms.
There are gaps and some contradictions in the data on the toxicity of false morels. Although false morels have been consumed in Finland for a long time, there have been no deaths from false morel poisoning in recent decades, and severe poisonings are rare. Based on animal studies, a person would need to consume several kilograms of false morels to suffer a fatal poisoning. On the other hand, the Finnish Poison Information Centre receives several calls each year about milder poisonings caused by eating false morels.
To better assess the health risks of false morels, more research is needed on their gyromitrin content and the effects of gyromitrin and its metabolites in humans.
More information:
Researcher Petra Pasonen, tel. +358 29 520 4007, firstname.lastname@ruokavirasto.fi
Read more:
Assessment of health risks of gyromitrin and methods to reduce it in false morels (Finnish Food Authority Reports 1/2025, in Finnish)