Since it came up in the Oyster Stout post I thought I would make an ingredient post on the subject.
I have brewed a beer using Horesradish Root (peeled).
I prepped the root by peeling and slicing paper thin using a razor blade.
Seems like it was on the order of 1/4 to 1/3 cup of root slices.
I then covered them in a pint canning jar with Everclear for a week long soak.
The everclear tincture was added to the Secondary.
There was some heat derived from the root in the venue of peppery/radish heat style.
Taste of the beer at the last sampling was a forward note of Turnip root.
So If you like sliced turnips this beer ingredient is for you.