Vegetable Fats in a Bar

Soon after I moved into my apartment I noticed the telltale signs of rodents, tiny little fecal pellets littering the stove, counters, and drawers. There was even a dirt smudge on the wall at the point where a gap between the sink and counter afforded a convenient place for the mice to dive out of site. I bought some snap traps and baited one with peanut butter. I immediately caught an enormous Peromyscus leucopus, more commonly called a white-footed mouse. I spent a summer live trapping mice in northern Michigan and had to weigh probably hundreds of animals, and I would estimate that this particular mouse might have tipped the scales at about 30 grams (i.e. a little over an ounce).  

Made with vegetable and animal fats since 1879After that I ran out of luck. The mice were able to lick the peanut butter off the treadle without tripping it. Every time I came into the kitchen to find the trap stripped clean and unsprung, I also noticed that a little more of the Ivory soap bar that I kept next to the sink had been gnawed away. Why were the mice eating the soap?

As it turns out Ivory soap, like a lot of commercial soaps, is made with a mixture of vegetable and animal fats. In the case of Ivory the animal is a cow and the vegetable is a palm tree (coconut palms, among others). In the simplest sense soap is made by mixing triglycerides (three fatty acid chains bonded to a glyceride) with a strong alkaline, usually lye (sodium hydroxide, historically derived from the ashes of hardwoods). The mixing the lye with the triglycerides strips the glyceride from the acids and puts it into solution as glycerine. The fatty acids in the soap are apparently an appealing source of calories for white-footed mice.

I placed the bar of soap in a high cabinet and baited the trap with a little piece of soap stuck fast to the treadle. In three days I caught (killed) four more mice. All of them were much smaller than the first one. I suspect that I wiped out a mother and her brood. So goes the war.  

All this got me thinking about soap making. It is an artisan practice in this area and the small batch locally made stuff is expensive. A little research revealed that historically both animal and vegetable fats were used to make soap with the Babylonians being the oldest reference, although their soap was apparently for treating wool not human hygiene. The Egyptians made soap to clean themselves, as did the Greeks and Romans.

After the fall of the Roman Empire soap manufacture seems to have become rather limited. The Crusaders are credited with reintroducing soap to Europe in the 10th century. They brought back a vegetable fat-based soap that came to be called “Aleppo soap” after its city of origin in Syria. It was (and is) made with a mixture of olive and laurel oils. Laurel oil proved difficult to find in medieval Europe (Laurus nobilis, the laurel tree, is found scattered throughout the Mediterranean region, but in small numbers) and a pure olive oil soap tradition evolved in both southern France and central Spain so that they became known as “Marseille” and “Castile” soaps, respectively.

Aleppo soap stacked for dryingFrom the Middle Ages to the Industrial Revolution the production of soap remained a small-scale regional industry, with higher quality, more expensive soaps being made entirely or largely from vegetable oils because they are milder to the skin, especially when “super-fatted” with supplementary oils during the saponification (soap forming) process.

Animal fat-based soaps tended to be those made at home by poorer people. Tallow (beef fat) and lard (pork fat) were both by-products of the butchering process, and by-products were not to be wasted. Before the advent of refrigeration it was advisable to use tallow and lard to make something before it “went off.” Mixing the fats with wood ashes produced a crude, harsh soap that was an effective cleanser, but left the skin raw.

The industrialization of soap production in the 18th century standardized the chemistry of saponification and was often carried out at higher temperatures, which sped up the process and cut down on the presence of residual lye. When meat packing became part of the industrial economy it increased the amount of animal fat by-products available and drove down the price of soap.

Dr. Bronner's is made with olive oilCastile soap, however, never quite went away, and with the rise of vegetarianism and animal rights consciousness has increased in popularity over the last 30 years or so. Dr. Bronner's Castile soap is well known to earthy-crunchy types everywhere as the potent liquid soap in the containers with all the tiny, cryptic printing on them. It has been manufactured in this country since 1929. The industrialization of cattle raising has made even non-vegetarians concerned about residual growth hormones and other chemicals stored in the animal fat that is then made into soap, and vegetable fat-based soap popularity continues to grow.