Field of Science

Sweet secrets

No one wants to run the cotton candy machine at the school fair, and now I know why. The plant booth is serene under the trees, the bake sale treats are neatly packaged up, even the lemon mom has only sticky hands. I am covered in pink, blue and violet spun sugar from head to foot. Really, I was seeing the world through rose colored glasses. And it gave me a lot of time to muse about sugar -- why is it so sticky?

What my recipe book calls sugar a chemist calls sucrose (or in very formal situations: [beta]-D-fructofuranosyl [alpha]-D-glucopyranoside). The stickyness of sugar is related to its hygroscopic nature (it will pick up water out of the air), which is a function of its molecular structure (for example the polar nature of the groups on the surface of the molecule - lots of OH groups.) and the physical form of the sugar (why cotton candy noticeably more hygroscopic than granular table sugar).

Biologically, the stickyness of sugar has certain advantages, as an article in Journal of Molecular Biology last year suggests.

And yeah - I'll do the cotton candy again next year!


  1. Table salt (NaCl) is also hygroscopic, but it doesn't get sticky. So, stickiness can't be just because of that.


  2. True, the ability to bind water is only part of the reason for sugar's adhesive qualities.


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