For many years, I have wondered how soap can clean dirt and grime away when it is made from grease and lye. How can these two unlikely chemicals produce the soft, fragrant, effective cleaning agents used in our bathroom, kitchen and laundry every day?
This short description is the result of brief research taking me to our public and community college libraries, online and personal communication with a local home soap maker.
Soaps are classified as types of detergents. They are made by a chemical reaction between lye, commonly known as sodium hydroxide, the major component in Drano, and animal fat, vegetable oils or grease that are heated to nearly boiling in a process called saponification. Historically, pioneers made soap by boiling beef fat (suet) with lye water created by mixing wood ashes from fireplaces with rain water.
The chemical reaction between lye and beef fat to produce soap is closely watched.
Photos by Robert Ungerer
Two bars of the author’s homemade soap look like butterscotch brownies.
Ancient records hint the Phoenicians used soap in 600 BC. In 1790, a French chemist produced cheap lye allowing inexpensive soap production and more universal use. In the middle 1500-1600s, soap was expensive and since the general European population had a common distain for cleanliness, it was only a luxury for the wealthy that used soap mainly as a cosmetic.
In the early 1800s, soap manufacturing became a thriving industry. During World War II, when animal fats were used in the war effort, artifical soap called detergents were made from vegetable oils and petroleum products. They unfortunately were not biodegradable and clogged sewage systems. By 1965, a biodegradable detergent had been created.
My personal experience soap making followed the pioneer methods with the specifics of the recipe available online. Lye was made by adding distilled water to hardwood ashes from my living room fireplace then letting it sit overnight in a plastic pail to leach out the lye.
The next day, the water was allowed to drip out a spout through several layers of cheesecloth into another plastic kitty litter pail. The fat was prepared by melting one pound of beef kidney suet in a frying pan in the kitchen. The lye concentration was tested by making sure a fresh egg would float in it. In my case, initially, the egg did not float so the lye required boiling to make it stronger.
A small amount of lye water was added to the melted beef fat and heated to near boiling in a stainless steel pot stirring frequently. More and more lye water and fat were added together until the mixture turned muddy and thickens indicating the chemical reaction was complete and soap was formed. At this stage, a fragrance - gardenia essential oil - was added.
The soap was poured into a parchment paper-lined 9-by-12-inch baking pan, cooled slowly, and usually aged one month to let the soap dry out becoming harder so it lasts longer in the shower. This project was an all-day affair for pioneers only done once or twice a year.
A simpler and more reliable home soap making recipe uses commercially available pure lye and lard heated on the stove until it resembles custard or pudding, adding fragrances and pouring into molds.
Briefly, for the curious, the mechanism of soap's action is as follows. The soap molecule has a derivative of lye on one end which mixes with water and a derivative fat on the other end which repels water but is attracted to oil or grime. This end attaches or surrounds oil which has dirt attached like on our hands. The mechanical action or rubbing of our hands with soap loosens the soap-grime combination which can be flushed away with water.
Soap acts like a bridge between the water and the dirt attached to the oil or grime on a surface. If enough soap is added to a jar of vinegar (mostly water) and oil salad dressing, shaken vigorously, the oil floating on top of the vinegar mixes with the water and disappears as if it dissolved in the water.
The next time you lather up your hands or hair with soap, appreciate the chemical reaction occurring as dirt is lifted off your body and washed down the drain.