What is it about unstable cocoa butter crystals that give chocolate that soft, waxy consistency? It’s not because “unstable” fat crystals are inherently softer or more likely to fall apart, though that would be a reasonable guess. One of the many interesting things about fat crystals is that they melt at the same temperature at which they form. So if you have a piece of chocolate that’s made up of a high proportion of unstable crystals, those crystals will have a melting point that’s right around room temperature, giving your chocolate a soft texture. Stable fat crystals on the other hand are formed at about 90 degrees. A piece of chocolate with a high proportion of those type of crystals will be harder at room temperature. It will have that nice satisfying “snap” as you bite into it, but of course being largely cocoa butter, will then melt in your mouth (since the melting point of cocoa butter is just below 98.6).
Oh, there’s just no end to chocolate chemistry fun.