I was curious, and found the ingredients for a 1992 bar of zest from an eBay photo. It was a mix of soap with the detergent sodium cocoglyceryl ether sulfonate. The current recipe is all soap but they added a couple of chelating agents: Pentasodium Pentetate, and Tetrasodium Etidronate. The problem with the new recipe is these chelating agents suck. The only thing that can jail Mg/Ca2+ faster than soap scum forms is sodium triphosphate, but that is no longer allowed and doesn’t belong in bar soap. It makes no sense that they changed the recipe.

Detergent products have gotten so bad that I have started mixing my own. I add STP to laundry and dishwasher powder and I never rinse dishes before putting them in the dishwasher. They come out sparkling. The whole phosphate thing is overblown. Phosphates promote algae growth, but the algae also breaks down loads of other contaminants. The problem can be mitigated with a simple fountain in the discharge pond.

Removal of STP from everything is great for plumbers as pipes are now all lined with sticky soap scum which means periodic snaking.