with the emergence of many roasts that are vastly different from the traditional italian espresso roast in the last decade or so this is a question i have pondered a lot
for me it isn’t taste. I’m happy for espresso to be bright & fruity, or dark and verging on sooty. it isn’t the presence of robusta. it isn’t necessarily a dark roast either. I’m pretty flexible on all of those elements
for me the critical element that must be present for a coffee to be called espresso is mouth coating
for a coffee to be called espresso it must be sufficiently dense and syrupy to ensure a coating of the inside of your mouth
when this occurs you should be able to taste the espresso in your mouth a full 30 minutes later, assuming you don’t eat or drink anything else after the shot
if the coffee is too lightly roasted this mouth coating doesn’t occur. you just get a short shot of filter coffee from an espresso machine instead
so while light roasts are ok, there is a bottom limit; the degree of roast must be sufficient for the oils in the coffee to be driven out into the cup during the extraction process
are you drinking espresso, or filter coffee roast put through an espresso machine?