While cream has an inherent structure of fat and protein to hold the foam intact, other ingredients require a little extra support. We wanted to create an aerated Brie cheese. We thought that its richness and smooth flavor would taste delicious lightened up as a foam. Our first experiment went flat: although it had a beautiful aerated texture when we first sprayed it from the can, it slowly collapsed on the plate. In order to create structure in our aerated cheese while still keeping a soft, melting texture, we looked towards agar, which would form a gel at a relatively high temperature, thus ensuring that our bubbles remained trapped in the cheese. The downside to using agar by itself is that it has a hard, rubbery texture and can fall prey to syneresis--expulsion of liquid--over time.