using slippery elm to prevent oil rancidity...

So, I was up the other night, herb-nerding out by randomly browsing through King's American Dispensatory, hoping to find something profound, when I stumbled across the entry for Ulmus fulva (slippery elm). It's an herb I've always thought of as rather straight forward: useful, mostly, as a protective, nutrient rich mucilage for dry and enflamed digestive problems. But I figured I'd see what King's had to say...

...and, look what I found, not under "Action, Medical Uses, and Dosage", but under "Chemical Composition":

"Dr. C. W. Wright states that, when fatty substances are heated for several minutes with slippery-elm bark, in the proportion of 1 part of the bark to 128 parts of the fat, and then the fat be removed by straining, this has acquired the property of not undergoing rancidity (Amer. Jour. Pharm., 1852, p. 180)."

Wow... that's rather fascinating...

I inquired on Henriette Kress's herblist, and was delighted to get a reply back from Susan Strasser (who I had the pleasure of meeting and sharing a nice lunch & nicer conversation with at the International Herb Symposium), who wrote back, saying, "I have the AJP from 1852 from the American Periodical Series, a database that the university I work for subscribes to. Here's the gist of the article, reprinted from the Western Lancet:

"Charles W. Wright, MD, of Cincinnati was talking to an early settler about what the Indians living there used to do, and mentioned that they had preserved bear's fat by frying it out, then melting it again with slippery elm bark, "finely divided," either fresh or dry, about one drachm of bark to a pound of fat. "When these substances are heated together for a few minutes, the bark shrinks and gradually subsides after which the fat is strained off an put aside for use."

He tried it with some other fats, and says it worked every time. "One specimen of butter, (an article which it is well known becomes rancid sooner than any other kind of fat,) prepared in this way more than a year ago, is as sweet, and as free from disagreeable odor, as the day it was made, having been exposed all this time to the atmosphere and change of temperature. Hog's lard may be preserved in the same manner.

This fact will be of much importance in the preparation of cerates and ointments, which can be thus protected from rancidity."

(again...) Wow.

So, practically speaking, by heating one ounce of slippery elm bark in a gallon of oil, we can prevent that oil from going rancid; seemingly indefinitely...

A good night of herb-nerding, eh?