There is a common misconception that espresso is a bean or a roast. Actually, the word espresso refers to a brewing method. Espresso simply describes coffee that has been made in an espresso machine. Beans are finely ground before they receive quick dose of high pressure (about nine bars) and warm water. This pressure and water combination extracts a small quantity of dense, flavor-rich coffee. A shot of espresso refers to about 7 to 9 grams of ground coffee, which results in about 2 ounces of brewed coffee. A double shot is simply a double quantity of ground coffee brewed to produce twice as much. If the thought of getting just a straight shot of espresso sounds dull, remember that they act as a barometer for the barista’s skill. As Gabrielle Rubinstein, co-founder of Joe the Art of Coffee in New York City says, "… The most challenging beverage to pull off is a straight shot of espresso. It's completely naked and any possible flaws that milk can hide are gapingly obvious."