Long before kitchen grease was used for biofuel, it was and still is used to make soap.
35 years ago when I started working in the restaurant business, the grease had always
been collected in a barrel out back when it was time to change the fryers. and about once
a month a company would collect the contents of the barrel to go towards the production of soap.
Been that way for the last 35 years.
When I first read the above, I was horrified. Then I realized that it actually said soap, not soup like my mind substituted.