The Scientific Reason Syrup Is Sticky
If you've ever been to a sugar house and watched the maple syrup production, you may have been surprised to learn that syrup is essentially just water and sugar. Molasses is the same, as is honey — just water and sugar. So why are these substances so sticky, when a few tablespoons of sugar dissolved into a cup of water is not?
According to Mental Floss, it's all about science. Water molecules are relativity slippery, so they slide against one another and against other items. Sugar molecules, meanwhile, are larger than water molecules and have a tendency to stick together. When you add only a small amount of sugar crystals to water, the sugar molecules detach from one another and latch onto the water molecules, so everything stays fluid and liquid. But when the sugar concentration is higher, as it is in syrup, you end up with some sugar molecules trying to stick to other sugar molecules, too, not just the water molecules.
The result is something not quite entirely a liquid, not quite a solid. The syrup is thick because the overabundance of sugar slows down the water molecules' movements and creates stickiness. However, syrup's chemistry is also affected by a few other factors that can cause the sweet fluid to behave differently.
When syrup is no longer sticky
You can use sugar and water to make other food items in addition to thick syrups. From thin simple syrup that flavors your favorite cocktail, to a rock candy science experiment that produces smooth, slippery hard candies, what makes these syrupy ingredients lose their stickiness?
While you can simply add less sugar to your sugar-water mixture for a more fluid simple syrup, you can also increase the viscosity of a concentrated mixture to make it less sticky. According to Chemistry World, the substance will only remain sticky until a certain viscosity threshold is reached. At this threshold, called the glass transition, the substance will transform into an amorphous solid and lose its adhesive quality. For example, if you cook most of the water out of simple syrup, more of the sugar will latch together to form a more stable, more solid, less sticky result — as seen when making caramel popcorn or honeycomb candy (via Food Crumbles).
As it turns out, water and sugar mixtures are incredibly versatile. The role they play in syrup's stickiness is all explained by chemistry.