I remember when I was little, getting a candy called Zotz at Halloween (they still make it, though it's changed); it's a hard candy that, when you get through the outer shell, fizzes. It's a real surprise if you don't know it's coming. It gave me the idea of making a chocolate that would have a similar surprise.
Zotz fizzes because of a reaction between malic acid (slightly apple-like in flavor) or tartaric acid (slightly grape-like) with sodium bicarbonate. Neither apple nor grape seems right to go with chocolate, so I decided to go with citric acid, which is lemony; it's a stronger acid, so the fizzing reaction is more powerful and that's why it's not used in Zotz.
I tried using other substances besides baking soda, like baker's ammonia (ammonium carbonate) - the horrible stench of ammonia was overwhelming. After all, it's the same thing as "smelling salts."
The challenge is keeping the acid and base from reacting before you eat it, which means keeping them from getting wet. Neither dissolves in fat, so I made a center of melted cocoa butter and coconut fat and added the reactants. It took several tries before I found how cooled and solid the fat had to be before I could incorporate the other ingredients; then it's a race to mix them before completely solid.
Then I thought I'd increase the surprise with popping sugar. The online suppliers were too slow to deliver, so I found a local store that sold Pop Rocks, which one can get now in chocolate flavor (though, alas, not lemon) and added them to the mix.
The last step was to enrobe the centers in chocolate, so I tempered chocolate and added lemon oil, as a hint of what was to come when one reached the center.
|Not my photo. Dipped chocolates all look the same.|