It's amazing the things people have learned over the millennia about how to work with things that grow on the earth.
Take olives for example. They're quite bitter right off the tree. You wouldn't want to eat one unless you're a glutton for gastronomic punishment. Over the years, many ways to deal with that bitterness have been developed.
You can use lye to cure olives. Lye was a common ingredient in soap for many hundreds of years, so you would have some around. Lower grade lye can...