Apple Cider Vinegar

Apple cider vinegar is one of the few ingredients whose government name and nickname are basically the same. It's apple juice that's been fermented twice: first into cider, then into vinegar.

Superhero or supervillain?

Superhero. Its superpower is acetic acid, the part that makes vinegar taste sour.

What it does in my shampoo bars

Apple cider vinegar is a classic in shampoo bars, and a lot of soapmakers add it for how hair feels on the rinse. In a soap-based bar, the lye reacts with the acetic acid and turns it into sodium acetate, a salt that can help the bar harden a little. That's also why the vinegar smell doesn't stick around.

The supervillain rumor

"Vinegar makes the shampoo bar pH-balanced." Not quite. Soap is alkaline, and a little vinegar in the bar gets used up by the lye, so the finished bar is still alkaline. An acidic vinegar rinse after washing is a separate step, and a different thing from vinegar inside the bar.