Lye comes from running water through wood ashes. I have no idea how they knew if the lye water was strong enough. My mom said that their soap was made from pig fat, not beef tallow, due to the fact that all their cows were milk cows. According to the soap information that I have, pig fat makes soap harder, but it doesn't suds as well as beef fat. There are all kinds of fancy soap recipes to be had on the internet, and lots of people really like making and getting the hand made soaps. Kathy