What exactly is espresso?
Well, besides being delicious and aromatic, simply put, espresso is finely ground coffee that’s brewed under pressure. Espresso beans are roasted, finely ground, measured into the portafilter, and tamped down to compress it tightly. 200 degree water is pushed through the coffee with added pressure for 25-35 seconds.
The result is 1 oz. of shot of bold, well rounded, full-bodied, concentrated coffee, with a rich flavor. The roasting process brings out more oils in the beans, so it can have a heavier feel. There are two layers to a shot of espresso. — the crema (carbon dioxide bubbles surrounded by water and oils) — liquid (made up of soluble solids, gases and insoluble solids)

But Is There More Caffeine in Espresso Than in Coffee?
Espresso 63 mg of caffeine in 1 ounce
Regular coffee 12-16 mg of caffeine in 1 ounce
So ounce for ounce, espresso has more caffeine. But if you drink 8 ounces of regular coffee, you get 96 to 128 mg of caffeine. Take in to account that all brew methods, proportions, beans, and roast levels have differing amounts of caffeine as well.
Espresso is coffee...the major differences between espresso and coffee: the roast, the brewing process and the grind. Espresso beans are roasted longer, ground finer, compressed and brewed under pressure. Refining and tweaking the brewing process is an art form, that requires knowledge, dedication and talent. And that's half the fun. The other half, of course, is drinking it!
