Espresso is created by using pressure to force hot water through a very finely ground coffee. This pressurized brewing system creates a very concentrated and intense product, which is why coffee espresso can form the basis of other drinks, including Americanos, lattes and cappuccinos. If you were to add extra water or flavorings in that way to a cup of standard coffee, you would be left with a very weak beverage. Intense does not, however, necessarily mean more caffeine. In fact, a shot of espresso, (approx. 1 ounce) has only half the caffeine of a cup of drip coffee (approx. 6 cups). Both drip coffee and espresso have an equivalent extraction: generally 20% of coffee grounds are extracted into the coffee beverage, but espresso is more concentrated simply due to less water being added. To create this intense beverage, pressure, generally a 9 BAR minimum, is used to force the small quantity of water through the grounds. Coffee espresso makers that claim to be espresso machines but rely on steam pressure, such as the Moka Express by Bialetti and only achieve a maximum pressure of 1.5 BAR and are not able to produce true espresso.