At my first cafe job, my boss sat me down with two freshly pulled espressos in separate shot glasses.
"Quick. Drink this one." I did. It was hot, syrupy, and deeply bittersweet.
"Now watch this one." We did. An amber foam slowly formed a thick layer on top of the drink. Then, we watched as the foam dissolved back into the espresso, leaving a lacy residue on the sides of the glass. The process took about a minute.
"Now drink this one." This time, the espresso was significantly cooler, yet still syrupy. But the flavor had definitely changed. The espresso tasted burned, almost ashy, and hardly palatable. I might have gagged.
"This," my boss instructed, "this is a dead espresso."
The good and the dead?
In your coffee journey, you may have heard something similar. The idea that if left to sit, an espresso will transform from the most lovely of beverages into something totally undrinkable. But what makes an espresso "die"? And do you really have to gulp down piping hot coffee in order to get the full experience?
Foam Is Where The Heart Is
It's hard to say exactly where the idea of "dead espresso" originates. It is most likely an offshoot of Italian espresso tradition. For the Neapolitan drinker, crema, the layer of foam on top of the liquid espresso, is an essential part of a great coffee. In fact, some Italian espresso enthusiasts swear that truly fine espresso should have a crema so dense that it can support a whole teaspoon of sugar for a minimum of a few seconds.
Unfortunately, time is the enemy of dense crema. The tight network of bubbles will break down as water evaporates and the emulsified lipids in the beverage interact with the foam.
But there is more to espresso than foam. What about flavor?
The new Dalla Corte Mina showing off its crema game
Heat Wave Is Not The New Craze
Temperature has a huge effect on how we perceive flavor. To me, the clearest example is an ice cold soda. When thoroughly chilled, a soda tastes refreshing and sweet. But when it is served at room temperature, the soda turns into something grotesquely saccharine – almost a cavity in a cup. This is because our body is better at detecting flavors when they are close to body temperature.
Items served piping hot or nearly frozen will be more difficult to taste in full. This does not mean a steaming hot mug of coffee is a bad thing. It just means that when a coffee is at its hottest, a drinker will experience temperature and body more than flavor.
Top competitive baristas know this well. If you watched the last few United States Barista Competitions, you may have noticed most baristas instructing their judges to wait to consume their espressos. Or they will often ask their judges to thoroughly stir their espressos to bring the temperature down. They know that if they want their judges to perceive all of their individual flavor notes, it is better to let the espresso cool.
Your author competing at the Western Regionals. Photo courtesy of Sprudge.com
A great espresso will have more flavors as the coffee approaches body temperature. A bad espresso won't be able to hide behind its heat and body as it cools. Still, there is a threshold for flavor and time.
As espresso sits, some important chemical reactions take place. All of the lovely oils and lipids that give coffee their rich body and long aftertaste will oxidize. This results in funky, off flavors of rancid fats (think musty or acrid). In addition, the mostly unperceived chlorogenic acids will continue to degrade into bitter and metallic quinic acids (think quinine in tonic water). Still, this process takes a fair amount of time to really have an effect on the beverage flavor.
Like most coffee stories, the science falls somewhat short of dogma or tradition. While your espresso will not die seconds after its pulled, the flavors will change over time. Should you use the espresso you made in the morning to make a latte in the afternoon? Probably not. But is it going to ruin your cappuccino if the espresso sits for a few minutes while you steam milk? If the coffee is quality and the shot well prepared, absolutely not.