Synseplaum dulcificum.

Miracle Berries.

The berries contain a protein called “miraculin” (really), which in and of itself also sounds kind of Potter-ish. Miraculin itself is tasteless, but once you eat it, it binds to your tastebuds. For the next fifteen minutes to an hour, the miraculin tricks your tastebuds into thinking that typically sour foods are, in fact, sweet.