Just saw this article on bracken in the Atlantic Online. The short version is that this fern actually contains carcinogens, but in varying amounts; a piece of the stuff raw may or may not contain much in the way of carcinogens. And once you cook it, the carcinogens are rendered harmless.
The poison is called ptaquiloside; if cows eat bracken, they may get cancer or pass some ptaquiloside into their milk. Creepy, huh?
But as Hank Shaw writes in the Atlantic article above,
a very normal cooking process for fiddleheads—blanching in salty water, then shocking in ice water, then sauteeing—renders the fiddlehead close to harmless.Indeed, that's the process Maangchi uses:
This is my method of soaking kosari.Well, I'm not going to go out and buy a bunch of the stuff, but it's good to know that in the amounts I eat of it, it's not really all that bad.
- Place kosari in cold water in a pot. 1 cup of kosari will need more than 20 cups of water.
- Boil it for 30 minutes and don’t drain hot water and let it soak. Wait about 6-8 hours. I usually boil it at night and drain it next morning."Korean Cooking Ingredients:Fernbrake"