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How do we know what to eat?

By Eric Boa

Exposed potato tubers accumulate more toxins in sunlight (in the field or in storage).



We’re coming to the end of mushroom season here in the UK. My most recent find was Lepista nuda, commonly known as blewits, sprouting in a Surrey woodland. My friend Steve and I had it in a rather nice sauce he prepared to go with steak. And yes, to borrow a phrase from Stephen Sondheim, “I’m still here”. In Africa the mushroom season is just starting. From Zimbabwe to Angola and Malawi to Tanzania, people are waiting – once the rains have started – for the appearance of edible mushrooms in woodlands. They are sold by the roadside and in markets and provide a useful extra income.

Some valuable species are traded internationally. The demand for Boletus edulis, known variously as penny bun, porcini (Italian), cèpe (French) and Karljohanssvamp (Sweden), cannot be met by local collectors in Italy, a major producer. Italian companies, many of which are based in the small town of Bogo Val di Taro, not far from Parma, import porcini from China. The owner of a mushroom stall in Emilia Romagna told me he was sceptical about these non-Italian porcini: “They don’t taste as good”.


Over half the porcini produced in Italy come from other countries, mainly China.



I doubt many will notice the difference when they open a packet of dried porcini and use them to impart a delicious flavour to pasta and other dishes. A more successful way to disparage the Chinese porcini might have been to question whether they were all the same species. A paper published in 2014 by the Royal Botanic Gardens Kew discovered three other species in a packed of porcini sold in London. My mycologist (a person who studies fungi) friend Enrico has told me the same thing.


Does this matter? Your packet of porcini will have been produced by a registered food company and bought in a licensed, regulated shop. Sales of porcini continue to rise. But as the authors themselves pointed out, “accurate diagnosis of components of our food … is essential for regulating global food trade and identifying food frauds”. Food fraud is a much bigger issue than you might imagine. White and black truffles are hugely more valuable than insipid truffle species, including Tuber sinensis. And yes, this comes from China.


I’ve studied and worked with wild edible mushrooms for over twenty years and consulted publications in and from many countries. The more I read the more I was astonished at the number of species eaten around the world. The latest estimate is around 3000 wild edible mushrooms. Note the ‘wild’: the vast majority will only grow in nature, often associated with trees, and cannot be cultivated. I didn’t appreciate either the variety of opinions on what was edible, or the passions this might arouse.


An Italian mushroom enthusiast was outraged that I’d published a book in which I reported the false morel to be edible. “I have asked FAO (the Food and Agriculture Organisation of the UN, the publisher) to withdraw the book.” I told him that I’d eaten false morels. A bit gritty and not particularly interesting. They were bought in a tin manufactured in Sweden. I was obviously still here. He persisted in telling me that false morels were “deadly poisonous”, as is clearly stated in all Italian mushroom guides I’ve ever consulted.


He's correct, but with an important caveat: false morels are poisonous when raw. As are many other foodstuffs, such as cassava and kidney beans. Cashew nuts are surround by a toxic oil which is removed during processing. In 1979 pupils at a London school were poisoned by potatoes. They’d been stored during the summer holidays and had accumulated natural toxins*. A friend was recently poisoned by courgettes grown from rogue seeds. I had my own glancing encounter when tasting a pasta dish my wife had prepared. We abandoned the pasta dish before it was served and suffered no harm.



The only way to tell if a courgette is bitter and unpleasant to eat is by licking a slice before cooking.


There has been no decline in eating courgettes or potatoes. Some will be aware of the risks and follow the advice to gently lick a cut end piece of courgettes before cooking, and to cut off ‘the green bits’ of potatoes. Others will blithely continue eating these vegetables. We easily cope with poisonous plants because they’re either processed or cooked, rendering toxins harmless. We regularly plant poisonous plants in our garden, such as laburnum, and celebrate ancient yews in churchyards with their pretty yet poisonous berries.


Wild mushrooms elicit a more hesitant and often hostile response. “Is it poisonous?” I was asked a few weeks ago, as a fellow visitor saw me examine mushrooms in a nearby arboretum. I had no intention of eating them; I was enjoying nature’s diversity. The fact the ink caps were probably edible was in my favour, but I really wanted to explain that poisonous mushrooms count for a tiny minority. Most wild mushrooms are simply not worth eating, either because they’re too tough to eat or simply tasteless.


My long encounter with mushrooms has made me ponder how human beings figured out what plants could be eaten. It is a remarkably haphazard and unscientific process, one based on the ‘lick it and see’ method. Or seeing someone else eat a berry, fruit, leaf or other plant part without apparent ill-effect. The same applies to animals and fish, even insects. A friend who worked in a game park in Nigeria rattled through the beasts he had sampled, a by-product of poaching and culling. Gazelles and other antelope were good; lion was unpleasant. Now you know.

Cooking and processing have played an important part in identifying foodstuffs, or we’d still be ignoring olives. There is no scientific test for determining what can be consumed but over the years a set of rules have emerged. The Universal Edibility Test was published by the US Army and adopted by trekkers and ramblers who may find themselves stranded in nature. It’s a common-sense approach of lick a little, chew a little, chew a bit more and so on. If, at the end, you’re ‘still here’ then it’s food, even if the taste is uninspiring.

Things can still go wrong. I found a type of oyster mushroom when out foraging in the north of Scotland with fellow mycophile, David. We cooked it when we returned home and ate a few. Tasted fine. “It’s an oyster mushroom”, I said, “and none are poisonous”. They’re sold in supermarkets, though not this particular species. David looked up Pleurocybella porrigens (Angel Wings) on Google, mainly out of idle curiosity, and discovered a mass poisoning in Japan in 2004: 59 people in nine prefectures in Japan became sick after eating the mushroom, of which 15 died from acute encephalopathy. A bell rang: I had read about it but had forgotten. Another person died from eating them in 2009. The average age of people who died was 70 and all were “medically compromised”.



Angel wings (Pleurocybella porrigens) collected in Darnaway Forest, Scotland.



It's still not clear what happened in Japan. The most likely reason was the build-up of a toxin under unusual conditions, much like the toxic potatoes eaten by the school children in London. We still eat potatoes, but history has been less forgiving of Angel Wings. All field guides mark P. porrigens as “poisonous”. Yet David and I still have our kidneys.

*School potato poisoning: https://www.smithsonianmag.com/arts-culture/horrific-tales-of-potatoes-that-caused-mass-sickness-and-even-death-3162870/

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