Bracken or Fern brake (Pteridium aquilinum and other Pteridium species) is known to have carcinogenic contents, also vitamin inhibiting components that cause other symptoms, including death, in animals that graze on it. It can spread rapidly from rhizomes, and in the right climate, also widely by fine seeds or spores. However, the shoots are widely used as a vegetable in Eastern Asia, a starch is extracted from the root that makes noodles and a Japanese sweet formerly eaten by Royalty, and it also makes a superb mulch and compost for the garden (see this summary document for example). How can all these things be reconciled and understood so that we can use it safely?
I’m interested in bracken because it grows widely here in the UK. In fact it is a persistent weed for much of the world’s landmass, excluding only extremes of temperature and water logged soil; it won’t grow in marshes. I’ve been researching it more recently and believe that it is possible to use it safely if you take some precautions. I’m not an expert, just an interested amateur, so if you have heard differently please comment below and share your information.
Bracken taking over sheep grazing
I’m not going to go into the problems caused to livestock eating bracken. If someone who is interested in livestock management wants to add more information that would be great. I understand that normally they will avoid it unless there is nothing else for them to eat. This has the effect of the bracken gradually taking over meadows unless action is taken to reduce it, although trampling on the emerging crosiers can reduce the growth somewhat. Because bracken has also anti-insect properties, there is little that will normally reduce the bracken itself.
Other uses of bracken include animal bedding, insulative underthatch for roofs, various medicinal uses, a dyestuff and fibre for basket weaving, See also Bracken.
Bracken fern shoots in spring
The main carcinogen and allelopathic component in bracken is ptaquiloside (PTA). The amount of PTA in bracken varies with the part of the plant and the time of the year. There also appear to be some strains of bracken in the USA and New Zealand that are entirely PTA free (ref.) although you would presumably need to have a laboratory test your bracken to be sure of this. In general there is most PTA in the growing shoots in spring, less in the mature stems and the least in the roots. The PTA is easily destroyed by the action of heat, and water. Blanching fronds in slightly alkaline boiling water for just 2 minutes was found to reduce the PTA by 65%, boiling for 20 minutes in water reduces it by 99%, reducing it to a level considered safe. Good practice appears to be to wash the fresh fronds, rubbing off the tips and stem hairs, strain, then boil 5 mins in fresh water, dry (2 days in sun) steam ½ hour, dry again (one day in sun). The shoots can then be stored for whenever you want to eat them. When it comes to cooking them rehydrate with boiling water, leave to soak overnight, then stir fry or cook into stews.
To be honest I’m more taken with the idea of extracting starch from the rhizomes. They contain about 65% starch by dry weight, although much of the fresh weight is water so the extraction rate is more like 5% from fresh rhizomes. However the amount of bracken root has been estimated to be up to 5kg dry weight per m2 in the UK (ref.). The starch can be extracted and stored to be used as a cooking ingredient. Also apparently Maoris and other Pacific peoples, as well as North American first peoples, pit roasted and ate the rhizomes as a vegetable, although online reports suggest that this is not palatable to modern tastes. The roots were also dried by the Maoris for ease of carrying during trips.
From this paper “products, mainly those based on rhizomes, were found to contain no PTA …... Rhizomes and rhizome-based products could be considered safe concerning PTA toxicity and when prepared from rhizomes collected in winter, which seems to be the practice in China”. There is more PTA in the roots in the autumn, as the nutrients from the leaves are being stored, rather than in spring when the new shoots are growing, but generally the amount of PTA is less than half that of the shoots (ref.) . Again much of the PTA will be leached into the water whilst extracting the starch, or destroyed during the cooking process.
To extract the starch the roots need to be cleaned of mud by scrubbing and rinsing with water, the roots are then crushed or minced, the starch is then rinsed out into water and the fibrous solids filtered off. The water is then left to settle overnight and the water poured off leaving the starch. This may need cleaning by rinsing with clean water and filtering 2 or 3 times. The starch can then be dried and used for cooking. This video is one I found that shows the full process:
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Alternately, a thin batter can be made from the starch and steamed to make pancakes which are then dried, then rehydrated and sliced to make noodles (more videos showing the process: https://www.youtube.com/watch?v=miMZwMiDSN4, https://www.youtube.com/watch?v=oR7SvmM7c-Y). The worst bit of processing seems to be the cleaning of the roots.
The starch is apparently somewhat like potato flour in character and is used in Japan to made warubi mochi, a kind of jelly confectionery coated in soybean powder. Because of the expense of pure bracken starch, which is available commercially from China and Japan ( example and another example) for about £100/kg these are normally actually made from blends of other starches.
Bracken competes with other plants in various ways. First there is the canopy it forms, which shades out other plants. Bracken can grow up to 6 foot tall in the UK. In addition the PTA washing off the top growth inhibits seed germination (ref.) although it is short lived in the soil, quickly being degraded by microbial action (ref.). So mulching with fresh bracken will inhibit weed seeds from germinating, but not affect established plants, and will break down to form good compost in time: my blog post on bracken compost.
There is a possibility that PTA can leach into drinking water supplies in high rainfall areas, and also be present in milk of cows that include it in their diet, which could theoretically be of concern in some areas (ref.). Spores are released from mature plants in hot weather, but are quickly washed out of the air by rain.
I think we can make a resource out of a nuisance, however I still wouldn’t suggest introducing it onto your land if it doesn’t grow there currently. Chances are it won’t be far away anyway and the landowners there will be only to happy for someone to take some away.
I apologise for the length of this post, I just thought people might like to have the information I have gathered in one place.
Having enjoyed gosari namul/fernbrake/ bracken fern in Korean meals many times, I had no idea I was flirting with danger!
This was very interesting from the perspective of having eaten it without knowing much about the big picture of the plant. I had only really heard of it otherwise for contaminated soil remediation.
"How fleeting are all human passions compared with the massive continuity of ducks.“ — Dorothy L. Sayers
I am guessing as a pioneer plant it produces plenty of organic matter that drops to the ground.
I hope that then builds the soil quality.
I have never thought of eating it though!
Every spring, I see people in foraging/gardening groups on Facebook talking about which ferns are edible and the dangers of bracken. I keep this link queued up to paste into all those discussions. Some of my favorite Sichuanese pickles have bracken in them.
Nancy Reading
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Location: Isle of Skye, Scotland. Nearly 70 inches rain a year
Christopher Weeks wrote:Every spring, I see people in foraging/gardening groups on Facebook talking about which ferns are edible and the dangers of bracken. I keep this link queued up to paste into all those discussions. Some of my favorite Sichuanese pickles have bracken in them.
Yes that link was one I found in my searches. I did actually try a (singular!) bracken fern crosier this spring. Being the first time, I boiled, soaked and recooked it three times, which I think was overdoing it in the end! It turned out quite tasteless. Maybe I've been brainwashed into being too scared of it still.
I'm still trying to work out how to harvest the rhizomes though. I'm thinking getting paid twice - by the land owner for 'clearing' the bracken, and then £100/kg for bracken root flour! Alternatively it could be a useful starch source in hard times. I'm a bit surprised there doesn't seem to be more of a history in the UK of using it as famine food, given how ubiquitous it is. I could only find a few references to medicinal uses of the root.
Invasive plants are Earth's way of insisting we notice her medicines. Stephen Herrod Buhner
Everyone learns what works by learning what doesn't work. Stephen Herrod Buhner
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