Thursday, August 02, 2012

Gels are not just protein-based

The American TV Chef Alton Brown was recently asked his opinion about the famous "Cupcake-Frosting-Is-A-Gel" incident, in which a TSA agent confiscated a woman's cupcakes because 1) the frosting was a gel, and 2) the amount of the gel was over the legal limit of 3 ounces.

Alton had this to say:
"You know what: Icing is not a gel. By definition, icing is not a gel. Because a gel—we get that word from gelatin, which implies coagulated proteins, so it is not. Technically frosting is a condensed syrup, so I would argue with TSA that they were out of their freaking mind."
I admire Alton quite a bit. His TV shows are both entertaining and informative, but in this case, Alton is clearly wrong. While it is true that the word gel does have its origins in the gelatin , the word has expanded it's meaning well beyond those limited origins. As was noted in the link above, hair gel as a word arose in the late 1950's, and many hair gels are not protein based. Further, Paul Flory in his Introductory Lecture ($) to the 1974 Faraday Discussions noted that there were 4 different types of materials that were considered gels"
  1. Well-ordered lamellar structures, including gel mesophases
  2. Covalent polymeric networks; completely disordered
  3. Polymer networks formed through physical aggregation; predominantly disordered, but with regions of local order
  4. Particulate, disordered structures
What this really means is something that rheologists have known too well for too long - gel is a poorly defined scientific term, one that is used to describe materials with similar macroscopic physical behavior even as the underlying microscopic physiochemical make-up varies wildly. This is approach taken by the TSA - they are concerned about materials with macroscopic gel-like properties, not what the chemical constituents are.

Lastly, it is possible that the frosting on these cupcakes was in fact a gel, as royal icing has egg whites in it. Egg whites have lots of water, but also the protein albumin, meaning that even under Alton's limited definition of gel, it would be a qualify.


Bend said...

Thanks for highlighting Brown’s comments (an aside, I’ve found it interesting to note the interest in gastronomy among those with professional chemical education). Thank you also for highlighting the broad class of materials that are gels. Going by Flory’s definitions, the TSA was clearly correct in identifying the frosting as a gel, but their enforcement of the limited gel rule seems inconsistent and perhaps capricious. I can think of several other “gels” (by Flory’s definition) that I’ve gotten past TSA with full security approval: my gel insoles for my shoes, the rubber outer soles of my shoes (gels by definition #2), my leather belt (by definition #3 and, as it was tanned, #2), the dookie in my toddler’s diaper (much more than 3 oz!). I’m sure you can come up with some more that TSA routinely ignores. By the way, I would gladly have left that dookie with security had they made a fuss.

John said...


The TSA appears to be only interested in soft gels, but it's smart on their part to not get into a fight about what is soft vs. hard.

The superabsorbant polymer in your toddler's diaper is also a gel. I imagine that any one diaper alone would exceed 3 oz., and parents always have backups, so that is also overlooked. Dido for adult incontinence diapers.