In a brackish episode of the PBS Digital Studios series Reactions, narrator Kyle Nackers explains why olives can’t be eaten raw or fresh off the tree. It’s due to oleuropein, an extremely bitter natural chemical that encompasses 14% of the fruit. In order to rid the olives of their bitterness, they need to be salted and packed in a briny solution. This process can take weeks, so olive producers turned to a chemistry based shortcut that removes the chemical in far less time.
it involves soaking the olives in sodium hydroxide. Good-old NaOH is commonly known as lye and it’s used in soap making. Instead of soaking out the bitter oleuropein over time sodium hydroxide speeds up its chemical breakdown to less bitter compounds …it takes a week or so to do its job depending on the process. Caustic lye doesn’t end up in your food since the olives are then thoroughly rinsed, then they’re packed in the salt brine that helps preserve them.
Fun fact, in the 1800s olive farmer Freda Ehmann found that adding oxygen to her lye solution caused her green olives to turn black. Thus the invention of black olives.