[Brake Fern, Fernbrake; Gosari (Korea); Warabi (Japan); Pteridium aquilinum]
A common fern in temperate climates, immature Bracken fronds are eaten as a vegetable in many parts of the world and particularly in Korea, Japan and parts of China. Native Americans dug up, cooked and ate the rhizomes from which the fronds sprout. These are still used in Japan, Sichuan, China and elsewhere, as a starch source (see noodles, below).
Bracken Fern is toxic to livestock when a significant part of their diet. For humans, fresh fern should be cooked (simmered 10 minutes) and eaten in moderation. One of the toxins is a thiamine inhibitor that can cause a vitamin deficiency if consumed for an extended period.
Bracken also contains a substance identified as a carcinogen
(ptalquiloside), and has been placed in the same risk category as
Coffee and Sassafras by the American Cancer Society. Study is ongoing,
and there appears to be some cancer correlation for Korean and Japanese
populations who eat fernbrake on practically a daily basis.
Ptalquiloside is volatile and destroyed by heat. Currently there is
insufficient data as to how much may remain in fresh boiled fernbrake,
or dried, boiled, soaked and cooked fernbrake. Basically, cooked
fernbrake seems safe enough for occasional use. Some varieties of
fernbrake, particularly in New Zealand, do not contain this substance.
The photo specimens are water packed and dried examples from a local Korean market. The dried is most used in Korea, because young fernbreak fronds are seasonal.
Water Packed These were up to 11-1/2 inches long and the largest stems were just under 0.25 inch diameter. I have found it best to trim fronds to 9 inches because beyond that they are likely to be hard and fibrous.
Dry Fernbrake: These were purchased from a Korean market in Los Angeles in a 6 ounce plastic bag, at 2015 US $3.99 for 6 ounces ($10.64 / pound). They take boiling and a long soak (see below), but provide an interesting flavor.
Yield: Dried fernbrake, boiled and soaked by the method given below: one ounce dried produces 6.1 ounces rehydrated. The fernbrake is reasonably tender after the boil and cool, but the yield is 5.4 ounces per ounce, so it clearly can still benefit from the 8 hour soak.
Korean cooking maven Maangchi recommends this procedure:
Fern Root Noodles