There has been some talk of using brewing roasts for espresso, some going so far to say brewed results can be matched in the machine.
For brewing, I roast to just before the end of first crack. Sweetness is intense, aroma vibrant, acidity balanced, body syrupy, with little to no roast flavors. I can easily say my brewed coffee is the best I've had.
For espresso, I roast to just before the beginning of second crack. As espresso, the espresso roasts are, well.... like espresso. Viscous tongue coating body, balancing between acid and bittersweet, tending toward a bittersweet finish. It's what most people would call good espresso.
As espresso, the brewing roasts require a very fine grind and are a different animal altogether in the cup. Heavy, almost dead weight body sitting squarely on the center of the tongue. Acidity in balance with sweetness (no pucker face), aroma intense with the origin flavors loud and clear. The experience is fantastic.... but the body is not the emulsification that in my perception defines espresso.
Obviously I show preferences to the clarity of a brewed roast as espresso. However I'm hung up on the body. Is it possible to get a viscous tongue coating emulsification of coffee oils from a very dense city roasted bean? Is it simply necessary to embrittle the bean with the density/cell structure change that comes from darker roasts in order to make espresso (as defined by being an emulsification) from it?