Since I've answered the question, "How?" about culinary foams for you, the next questions become, "Why? Why? Why?" The answers can be found in Spain. Spain is a rascally ground breaker that invented California and circumnavigating, so it makes sense that they also put food foam on the map. A modern, deconstructive Spanish chef named Ferran Adriá popularized culinary foam in an effort to help Spain start discovering things again like they did in the good old days.

Adriá nosed out that using flavored foam (sometimes ambrosially referred to as espumas) on his creations enabled him to add or intensify taste without changing the essential composition of his dishes. In other words, you can plop a little flavorful foam on top of a piece of beef and it won't go running like bulls all over what you just worked so hard to put together, as sauce is wont to do.

Literally a mouth watering foam?

Culinary foam is part of a broader movement called molecular gastronomy. If you're interested, there's a book called "Molecular Gastronomy" that goes on and on and on about it. The book's author is named Hervé This. If my last name were This, I would have felt compelled to name Margot, my older daughter, Thatanne Theotherthing This. And little Greta's first and middle names might have been, Now Hear. Anyway, in short, molecular gastronomy is a way of making your meal look more like the colorful cubes and spheres that they ate off trays in the cafeteria of the Starship Enterprise: 

Didn't an intense fight break out right about now in this scene?