Reader Bailey wants to know why she should go to the trouble of making actual poured fondant for her black and white icing instead of just using a simple powdered-sugar-and-water mixture. It’s a terrific question and the answer is all related to crystals. Sucrose crystals to be precise.
Icings are forms of crystalline candy that flow…at least for a while…until they set. Their consistency, the way they feel in the mouth, is a factor of the size of the crystals they contain. The smaller the crystals the smoother the icing feels on your tongue, and the more consistently it behaves as a topping.
Simple icing is made by — simply — stirring powdered sugar into water. This makes a sort of slurry of small sugar crystals and a thin syrup of water and free sucrose molecules (plus a little corn starch, the anti-caking agent that’s in powdered sugar). It has a pourable consistency when you first make and apply it, but shortly the forces of crystallization — random crystallization — take over and the texture starts to change. The sucrose molecules in the solution start to find one another and stack up like LEGOs forming all sorts of odd shapes, many of them very large. As this occurs, water is forced out from between the crystals and evaporates. The icing becomes firm, then brittle and crunchy. The once-smooth and glossy finish turns dull as the syrup in it disappears, and starts to warp and buckle. The end result is a top coat that looks worse the longer it sits and shatters and crumbles when you bite into it. It also feels grainy in the mouth.
Fondant gives a much different result because it’s made differently. It starts out as a dense, hot sugar syrup, a so-called supersaturated solution which is created with heat. Boiling water, you see, will accommodate a lot more dissolved sucrose that cold water will, over twice the amount. So right away you’re dealing with a syrup with a much lower moisture content (only about 13%).
But that’s not where the advantages end, oh no. For if you cool a supersaturated sucrose solution and then agitate it briskly, you get a controlled crystallization that produces crystals of a size so small that they don’t register on the human tongue. Better still, those tiny crystals end up floating in a dense syrup of invert sugar (basically non-crystallizing glucose and fructose molecules) and water. That small crystal-syrup combination keeps the fondant not only smooth and uniform but pliable even after it’s been applied. Sure, it’ll still form a bit of a crust when it sits for a while, but it won’t lose its luster and/or crack like a coating of simple icing will. Plus is feels silky when you eat it.
Is poured fondant absolutely indispensable for a doughnut or a black and white? Not for home cooks it isn’t, no. But black and whites with real poured fondant absolutely do taste better. ‘Nuff said.