File' (pronounced fee-lay) is the traditional table condiment used on gumbo.  Because of this, sometimes it is called "gumbo file".  The early Cajuns learned to use file' from the Choctaw Indians of the Gulf coast, who evidently used it to thicken soups.  File' is ground sassafras (Sassafras albidum) leaves. 

Sassafras albidum (for more complete information)
Sassafras is a small inconspicuous deciduous tree.  The tree usually grows to 20 to 30 feet tall, however some specimen may get much taller under ideal growing conditions.  Sassafras has light green to medium dark green leaves.  The leaves are very characteristically lobed.  The leaves range from entire, to bilobed to the characteristic trilobed leaves.  As an aside, sassafras root and bark are sources of the flavoring for root beer. If you dig up roots and peel back the bark, it will smell like root beer.  Parts of the sassafras plant contains safrole, which may be carcinogenic.  However, the leaves do not contain safrole so they are save for making file'.  Sassafras can be harvested in its native range throughout the southeastern US, with its range extending into East Texas.

Sassafras albidum
Sassafras albidum
Sassafras leaf shapes
Range of leaf shapes: from entire to the characteristic trilobed leaf.

I have a former graduate student who is from East Texas, and sometimes he brings me a bundle of sassafras leaves in the fall, which I use to make fresh file'.  Recently I found a small population of sassafras trees growing along a creek bank on our hunting club in northern Brazos county.  It is about a mile from the Navasota River and has pockets of sandy soil.  So I now have a local source of sassafras to make small batches of file'.

Make your own file'
You can make your own file'.  In Tony Chachere's Cajun Cookbook, he says it is best to harvest the leaves during a full moon.  I harvest small limbs in the fall of the year before the leaves start turning color.  I make file' as follows.
How to Make File'
Harvest young shoots
Cut small limbs from the tree in the fall before the leaves start turning color.
wash leaves
Clean the leaves
Spray off the leaves with water.
Dry leaves
Dry the leaves
Hang the limbs in a cool, shady place to slowly dry.   I usually hang them indoors at home or at work. Do not dry the leaves in bright sunlight, which can cause fading.
remove leaves from stem
hand crush leaves
Remove leaves from the stem
Remove the leaves from the stems.  If you are patient, remove the petioles (stalk of the leaf) from the leaves.

Crush the leaves by hand.

put leaves in blenderblend leaves in blender
Grind the Leaves - Small Batches
For small batches, I use a blender. The dried leaves are ground until you get a fine powder.
sift ground leaves
file' - ground sassafras leaves
Sift the Ground Powder
Sift the ground powder to remove larger pieces (larger veins, petiole pieces, etc.)
grind in Wiley mill
Grind the Leaves - Large Batches
For large batches, I use a Wiley mill to grind the leaves.  A Wiley mill is used to grind plant tissue for laboratory analysis.  It does a much better job than a blender, and you can make the powder as fine as you want, and the finer the better.
bottle of file'
Store the file' in a well sealed jar.  File' can be stored for a long time, as long as it is kept dry.  File' tends to loose some of its flavor over time, so I try to make a fresh batch every year. I also store it in the refrigerator to keep it as fresh as possible.

The one branch of sassafras shown above yielded this amount of file.  It does not take a lot of leaves to make a jar full.  A small jar of file' goes a long ways, because not much is used in a bowl of gumbo.

How to use file' as a table condiment on gumbo
bowl of gumbo
File' is sprinkled on the surface of  your gumbo at the table.  File' makes the gumbo thick if you let it set for awhile.  Don't add file' to the gumbo during cooking or else it will make the gumbo thick and stringy.  You can add a pinch to the pot at the very end of cooking to thicken the gumbo - but don't add too much or add it too early while the gumbo is still boiling.
©David Wm. Reed