The Marble Slab Paradox

At the Fudge House, we were told, the first batch of the day seems to take forever to get firm, but once a few batches of fudge have warmed up the marble slab, the fudge begins to set faster.

It seemed pretty strange to us that fudge would set faster on a warm slab of marble than on a cold one. After all, as the fudge cools, sugar molecules start coming out of solution and forming solid crystals. Since crystallization is what turns fudge from liquid to solid, shouldn’t more rapid cooling lead to more rapid solidification?

To solve this mystery, we talked to Dr. ZoeAnn Holmes, professor of nutrition and food management at Oregon State University. She confirmed the phenomenon and explained that when fudge cools slowly on a warm slab, more crystals have a chance to form. With a higher number of microcrystals, the sugar has more sites on which to crystallize, and so crystallization ultimately happens faster.

In comparison, fudge cooled quickly on a cold slab has less time to form the tiny seed crystals that will grow as the fudge cools. With fewer crystals to work with, the sugar in solution actually takes longer to solidify.
What does this mean for the home fudge chef? Our experience is that we get pretty eager for fudge once we’ve started cooking it, and we hate having to wait for it to cool down to lukewarm before beating it, as instructed in most recipes. A few of us have attempted to help the cooling along by putting the hot fudge in the fridge. But according to what we learned from Professor Holmes, instead of helping to speed things along, this probably prolongs the time it takes to reach the "beating" stage of fudgemaking.

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