Dan Souza asked: “What’s the difference between bread and ice cream?”
Good tricky question!
Bread and ice cream are only occasionally seen together—those occasions being ice cream sandwiches and a surprisingly delicious rye-bread-infused ice cream that I learned to make from Francisco Migoya (author of Frozen Desserts and Modernist Bread) and have never forgotten. It’s not like you’d confuse one for the other. They are both wonderful foods with more differences than similarities.
Until you take a look at their internal structure. For, as you well know, Dan, bread and ice cream are both foams.*
The leavening in bread inflates thousands of tiny gas bubbles during the rise, turning a stodgy, solid dough into a porous, light, eatably soft structure, which baking then sets in place. Without that unsung ingredient air, bread would be hard to bake and too dense to eat (except as crackers).
Ice cream gets its air whipped in by the churning process, which makes it soft enough to eat. Half a pint of ice cream may be air (called “overrun” in the business); more expensive ice creams or gelati tend to contain less air, maybe 35 percent. Without air, ice cream would be a tasty treat that you would cut with a knife and chew off the cone.
Other culinary foams are more obvious: whipped cream (air held by milk fat), meringues (air held by egg whites), marshmallows (gelatin), the head on your pint of beer (dissolved protein from the malt). Mousses and soufflés, too, and even puffed rice and popcorn: Examine them under a microscope, and they turn out to be starch-based foams.
Swiss cheese? Arguable.
* The word “foams” got a lingering connotation from the work of avant-garde chef Ferran Adria starting in the mid-1990s. As part of his tireless experimentation with textures in food, he discovered that putting a savory sauce in a whipped cream whipper turns it into a savory foam. It’s a good technique, but it’s become shorthand for silly frothy culinary play..