The phrase "edible foam" either conjures up images of overwrought and overplated kitchen chemistry experiments or the top layer of a freshly poured beer. But it also describes the most standard of foods: bread. Because bread is also a foam.
In the latest Lucky Peach, Harold McGee author of the food science classic On Food And Cooking gives a tidy explanation of what foam is, and why bread (and ice cream, as well) both fit into the category:
It is, because foam, essentially, is air bubbles trapped in different phases. The foam on top of a beer—those are air bubbles surrounded by liquid. When you churn an ice cream mix, you are driving air bubbles into it. And then the mix freezes and you end up with a bunch of bubbles inside a solid matrix. The same is true of bread. You end up with bubbles inside a semi-solid matrix in the dough. Then you bake the dough and solidify the matrix, and you end up with a solid foam. Gluten is the thing, in the case of bread, that allows you to trap those bubbles and make that foam.
You can read the whole thing, including some of the chemical background of our old (and unreasonably delicious) friend gluten, right here.
Image: Scott Bauer, U.S. Department of Agriculture.