What is Espresso?
Coffee connoisseurs disagree over the exact definition of what qualifies as espresso. The simplest way to understand it is to think of espresso as coffee concentrate. Of course, that hardly does it justice. Espresso is the result of forcing hot water (190°-196° F/88°-91° C) through finely ground coffee at extremely high pressure (around 9 bars, or 130 Psi). The high pressure extracts the most flavour possible out of the beans. This produces a small amount (1.5-2 oz) of very strong, rich coffee.
When done right, espresso is smooth and syrupy with a layer of golden crema. It can be enjoyed straight as something of a “coffee shooter”, but more often it is used as the base for a whole range of specialty coffee drinks. The most common are Lattes, Cappuccinos and Americanos.
There are several brewing methods that produce small amounts of very strong coffee; some folks have tried to pass this off as espresso. Such methods include the Moka Pot and the AreoPress® coffee brewer. While these methods make great coffee, they do not make true espresso. These methods are not capable of producing enough pressure to extract all the flavours out of the beans. Thus what they make would be better described as “espresso-style” coffee.