Reader Rainey writes in to ask me to expound a little on the phenomenon of crystallization, specifically in sugar (marshmallows) but also in chocolate. Those who know me know that if there’s one thing I like to do, it’s expound. So let’s take the first part first.
Sugar crystals can be a blessing or a curse depending on the outcome you’re after. They’re great for, say, rock candy, but not so great for marshmallows. Marshmallows are made from table sugar (sucrose), which is especially crystal-prone for the simple reason that its molecules are so similar to one another. When you have a lot of similar molecules in very close proximity to one another you get a sort of LEGO effect: the molecules stack up on each other and whammo: crystals. To prevent that from happening you need to bring some random flotsam and jetsam to the party: molecular junk that will get in between those very small, similar molecules so they won’t be able to lock together. This is the service that corn syrup performs. It’s made up of a hodgepodge of longer-chain sugars which get in between those little sucroses, preventing them from arranging themselves in orderly stacks.
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