Ferran Adria’s espresso foam, named “Espesso”, is indeed a fascinating concoction, created in cooperation with coffee producer Lavazza. The word espesso is a combination of espresso and the Italian word spesso, meaning thick. Just luck at the thick lucious foam.
Espesso has been available in Europe since 2002 (anyone know where?), but was just recently introduced in the US. Appearantly, the foam is served warm in Europe, but has been served cold in Chicago, at Lavazza’s three locations there.
According to the reports, espesso is made from espresso and a “secret” ingredient. The ingredients are mixed and left to settle for 12 hours under pressure. The product is then dispensed from the iSi Gourmet Whip (more info here, the propellant gas is nitrous oxide, N2O). As a chemist I certainly wonder what the “secret” ingredient is? If it is true that espesso has been served both warm and cold, they would need to use a thickening agent which is not very sensitive to temperature. Also, it appears that the foam once served is not stable for more than a couple of minutes.
My best guess would be xanthan and guar gum, or possibly a combination of the two. These hydrocolloids show thixotropic properties – when subjected to pressure/agitaion they soften, but then they jellify again afterwards. In other words – they could be easily dispensed through a siphon and would then solidify in the cup. Also, xanthan and guar gum are relatively temperature independent with regard to their thickening properties. Check out the INICON manuals on texture for great (and FREE!) information on these and several other hydrocolloids.
Update: The Lavazza homepage now features a video and a tool to find your nearest Espesso!