Soap as the backbone of civilization

Question

The world order went down and humanity was pushed back into an post apocalyptic society (no nuclear fallout). Most of humanty vanished. Only the old ones can remember how it was to have electricity. (6-7 generations)

Right after the collapse, most things were gathered such as food cans, drinking water etc. Over the time, people got independent from this gathering in terms of food, metal works, construction etc. The biggest cities have about 50.000 habitants.

A mid aged man, which never saw humanity at its peak, remarked that the supplies found went to a minimum. In his childhood, food was plenty compared to now, but people found a way to work around that. The only thing he misses is hygienics. People forgot how to handle waste, disease and filth.

He knows he can't change the world, but wants to start somewhere. So he decided to reinvent "soap". (It's not like he knows how to and the name, but it's about something so people are (easier) able to clean them self and their surroundings)

The question is, how to produce Soap in such a setting? What could happen, so he gets the first clue, how to do it?

Answer 1

There is a Roman legend that soap got it's name from Mount Sapo, where the fat and ashes from animal sacrificed there were washed into the river by rain. People washing clothes in the river found their clothes were easier to clean. Maybe your inventor washes his clothes downstream from a place that butchers and smokes meat.

Fat or oil mixed with alkali from ashes is one of the earliest formulas for soap. The things your inventor needs to make soap are ashes from a wood fire and tallow (fat) from an animal.

Water poured through potash (hardwood ash) produces water with lye (alkali). When mixed with fat and boiled, they combine and produce soap mixed with glycerine. The complete process is described at https://en.wikipedia.org/wiki/Soap and http://www.humantouchofchemistry.com/how-was-soap-invented.htm.

Answer 2

Don't get too wrapped around the axle about soap. Proper hygiene also consists of getting filth and waste products away from your dwellings and more importantly away from your water supply. The practice of using human and animal waste in the fields as fertilizer will have to be carefully controlled as well. Depending on the local climate, leaving it to "bake" in the hot sun will go a way to sterilizing it, or plowing it under and then planting a cover crop like clover to prevent it from washing into the river during the rainy season, and leaving the field fallow for a year before planting a crop will make it harder to spread diseases through consuming contaminated plants.

The ancient Greeks and Romans did not have soap at all, and generally washed with clean water, and then had their skin oiled and the layer of oil "scraped" off using a device similar in effect to a spatula. Many other ancient civilizations were generally hygienic without the use of soap either.

So if your guy is interested in better living, inventing or enforcing garbage collection, ensuring human and animal waste is safely disposed of away from water sources and even just rinsing off in clean water (hot is nice but not absolutely essential) will go a long way to dropping disease rates and making life that much better.