WOODS TO KNOW: Kentucky Coffeetree

WOODS TO KNOW: Kentucky Coffeetree

Kentucky Coffeetree (Gymnocladus dioicus)

by Peter MacSween

Most woodworkers think of exotic woods as having come from overseas, perhaps from some tropical rainforest. But the forests of North America are home to many non-commercial species that find there way into the workshops of curious craftsmen. Kentucky Coffeetree is one of these woods and is worth considering for many woodworking projects. 
Kentucky Coffeetree grows in a wide range from southern Ontario south to Louisiana and Kentucky as well as Pennsylvania west to Oklahoma and south Dakota. The tree is capable of growing to 100 feet with diameters approaching 3 feet. The trunk can be short since it has a tendency to branch at heights above 10 feet.  It's easily recognized by its large leaves which are the largest of any tree in North America. The leaves are compound, up to 3 feet long with many leaflets  The tree sheds its leaves very early in the fall and will remain dormant for 6 months. 

Kentucky Coffeetree gets its name from the practice of roasting the seeds to produce a coffee substitution. Roasting is essential since the leaves, sprouts and seeds are poisonous. Roasting inactivates the poison in the seeds rendering them edible. The seeds are encased in a pod that is incredibly hard, often compared to 'jawbreaker' candy. Animals will not eat these seeds, and they are too heavy to be transported by the wind. This probably accounts for the trees scarcity as the seeds will stay close to the mother tree where it is difficult for young trees to grow.
Some biologists now believe that extinct mammoths and mastodons were able to crack the seed pods with their powerful jaws releasing the seeds. Similar behaviour is seen with African elephants today.  Mammoths and mastodons are extinct, so the Coffeetree depends on the seed pods decaying naturally, a process that takes a minimum of 2 years. The tree will also propagate via root suckers which give rise to small groves of trees interspersed within its range. 
The wood dries well with little degrade, but it can be prone to ring shake. This is a separation of the growth rings within the tree. Once dry thought, it is considered stable  The wood is hard, dense and ring porous, resembling ash, the oaks and especially honey locust. The grain is usually straight with a coarse texture. The very small yellowish-white sapwood is distinct from the heart. The heartwood is a subtle reddish-brown to a more colourful orange-brown. The pith of this tree can be quite large and this may contribute to formation of open knots in lower lumber grades.

Kentucky Coffeetree end grain
Coffeetree is considered easy to work and machine. Irregular and figured grain is rare so planing and routing should be easy. It is dense, so it can quickly dull tools. It glues, screws and nails well.  Watch clamp pressure carefully during glue-ups to prevent squeeze out and starved glue joints. Being ring porous it stains beautifully. It can produce a highly polished surface although grain filling may be required. 
Coffeetree has many uses. It is durable so it has been used for large building timbers, fence posts and railway ties. It has also been used for interior trim, cabinetry and makes beautiful interior paneling. It is scarce; but reputable wood dealers within its range should have some. It is a little pricey for a domestic species but is less expensive than imported woods.
Woodworkers looking for a new material to work with other than the usual suspects of walnut, cherry, maple and oak should consider Coffeetree. Incorporating new species is interesting and fun for woodworkers and gives each new piece an interesting story. Many native North American trees are overlooked and using species such as Kentucky Coffeetree can deepen our appreciation of the diversity of the North American forests.
Average Dried Weight42 lbs/ft³A measure of its weight at 12% moisture and an ambient temperature of 70°F.
Specific Gravity.67A measure of the ratio of its density compared to water (at 12% MC)
ShrinkageRadial: 4.1
Tangential: 7.6
Volumetric: 11.9
Radial (the amount of crosswise shrinkage);
Tangential (the amount of lengthwise shrinkage);
Volumetric (the total amount of shrinkage.)
T/R Ratio1.9A measure of the uniformity of tangential to radial shrinkage.
Janka Hardness1,390 lbfA measure of resistance to denting and abrasion.
Crushing Strength6,600 lbf/in2A measure of compression strength parallel to the grain.
Heartwood an orange to reddish brown. Yellowish white sapwood is very narrow and well defined against heartwood. Overall appearance and grain pattern similar to ash or oak.
GrainStraight and porous.
TextureCoarse and uneven.
Coffeetree has good working characteristics, and nearly every machining operation can be done with good and expected results. Glues, stains, and finishes well.
Furniture, cabinetry, fence posts, and utility wood.
PriceSupplies can be erratic. Check with your local dealer.
Photos and Specifications Courtesy of: The Wood Database