Not a recommended beverage
In The Kentucky Warbler, James Lane Allen writes an amusing anecdote about a young man, ignorant of nature, who ventured into a Kentucky forest. He was unable to identify most of the trees, but he was sure he would recognize a Kentucky coffeetree (Gymnocladus dioica).
There was one tree he curiously looked around for, positive that he should not be blind to it if fortunate enough to set his eyes on one —the coffee tree.
That is, he felt sure he'd recognize it if it yielded coffee ready to drink. of which never in his life had they given him enough. Not once throughout his long troubled experience as to being fed had he been allowed аз much coffee as he craved.
Once, when younger, he had heard some one say that the only tree in all the American forests that bore the name of Kentucky was the Kentucky coffee tree, and he had instantly conceived a desire to pay a visit in secret to that corner of the woods. To take his cup and a few lumps of sugar and sit under the boughs and catch the coffee as it dripped down . . . No one to hold him back ... as much as be wanted at last . . . The Kentucky coffee tree — his favorite in Nature!
Source: The Kentucky Warbler (p.126-127) by James Lane Allen
This young fellow (had he been a real person instead of a fictional character) should have looked for a tree with large, heavy, purplish or reddish-brown pods. Inside a big pod from a coffeetree, he might have found up to 6 or 7 flat beans, as large as a quarter in size.
When dry, the coffeetree's beans take on a greenish-brown color. Perhaps the brownish color is what made the early settlers think that the beans -- roasted, ground, and brewed -- might yield a coffee-like beverage.
It seems that the coffeetree beverage was abandoned as soon as possible. In 1869, John Claudius Loudon wrote, "The seeds were, at one time, roasted and ground as a substitute for coffee in Kentucky and Tennessee; but their use in this way has been long since discontinued." (Source: An Encyclopaedia of Trees and Shrubs, p. 255)
Julia Ellen Rogers, writing in 1905, was a little more descriptive. "The pioneers of Kentucky made out of the seeds a beverage to take the place of coffee. We may well wonder how they ever ground these adamantine beans, and how they ever drank a beverage as bitter as it must have been." (Source: The Tree Book, p. 338)
The native Americans roasted the beans and used them as food. Roasting the beans seems to be an essential preparation before consuming them. Cystisine, a toxin found in the beans, is probably broken down by the heat during the roasting process.
Sprouts, leaves, pods, and beans of the Kentucky coffeetree are poisonous to livestock, and cystisine is suspected to be the toxic agent. If a pasture contains a Kentucky coffeetree, it is wise to place a fence around it. The tree is rare, so it should not be destroyed, but livestock, pets, and people should be prevented from consuming any part of the tree.
A good image of a Kentucky coffeetree pod
A good image of Kentucky coffeetree beans