This doesn't answer your question, but I thought you might find it
interesting.

I watched an episode of "SurvivorMan" on Discovery last night. It's a show
narrated by a guy who likes to lose himself in the wilderness and test his
survival skills. In this episode, he found an edible root (looked more like
a bulb to me) - can't recall which plant it was - and tried cooking it to
make it more edible/digestible.

First, he put a root on a stick and roasted it over the fire - but it
retained all of it's bitterness. It softened and puffed up just like a
marshmallow, but - at least to him - it was still inedible.

Then, he boiled the roots in his hat (I kid you not). First time I've seen
someone actually accomplish this feat. The hat (obviously waterproof) was
filled with water (like a hide might have been), and heated rocks were
added until the water started to boil. He would cover it, let it simmer for
awhile, add another rock, let it simmer, and so on. Eventually, the root
was very soft, and had lost much of it's bitterness. He still grimaced at
the taste, but it apparently satisfied his hunger.