So then, after all the hubbub about corn syrup we finally get to the nitty-gritty about what corn syrup does in a petit four glaze (fondant). And it only took me a week.
If you were around for yesterday’s post about what makes corn syrup thick, you’ll remember that one of the defining characteristics of this type of sugar syrup is that it has a small but critical proportion of long-chain sugars left in it. Those long spindly molecules do more than just give corn syrup a thick, gooey texture, they stop it from crystallizing. How do they do that? Well if you remember previous posts about crystallization, you know that crystals form when like molecules begin to mass into 3-dimensional shapes. Long chain sugars prevent this by simply getting in the way, like Sister Aquinata between me and Jane Kravicek at the Sophomore dance. The molecules stay separated, and so they flow.
This is the utility of corn syrup in a poured fondant, where you want some crystallization, but not so much where the whole coating hardens into one big crystal (which would shatter when you took a bite). And so you introduce a few spoilers, microscopic nuns, if you will, into the mix. While they can’t ruin everybody’s fun at one time, they can cause enough trouble such that you attain a nice mid-point between a runny syrup and crumbly, crunchy sugar: a firm yet pliable coating.