Ha! A web page where a geophysicist explains how fudge works. Finally I can use my degree to understand why yesterday's batch of coffee penuche was grainy.
(The answer was that I didn't wash down the sides of the pan, and then furthermore I cooled the fudge in the pan, giving the crystals on the edge plenty of time to take over my whole batch of fudge. I'm new at this. But hey, I've finally turned a corner on breadmaking. Maybe one day my candy will be up to par, too.)
P.S. The penuche is still good to eat, just not "right."