That fantastic question from reader Frans. Fantastic because that word gets thrown around all the time when people talk about food science, but no one usually bothers to explain it. To be wholly accurate, starch doesn’t really “gelatinize” (it technically takes protein to make gelatin), it gelates, though the effect is largely the same. Which it to say it causes liquids to thicken, even to the point that they become semi-solids.
In the kitchen, starches are delivered to us in the form of very small granules. Wheat flour or corn flour, which are nothing more than tiny pieces of endosperm (the energy storehouse of a seed). Tiny as these granules are, they’re made up of hundreds or even thousands of individual starch molecules. Think of them as bundles of very long reeds or strings.
Combine them with water and heat them and something very interesting starts to happen. Water molecules begin to work their way between the strands, prying them apart. That makes room for still more water, and the granule swells. As it does, individual starches start to break off, and the long stringy molecules disperse into the water where they begin accumulating like webs. They don’t chemically bond to one another like proteins in gelatin, but the tangling effect is just as good. The flow of the water molecules becomes restricted and mass begins to solidify.
That in a nutshell is starch gelation, and it’s as crucial to the formation of the crumb of cakes and breads as it is to the formation of a gougère. Pretty cool when you think about it, or am I just a nerd?