Coffee beans themselves have little to no taste at all. The flavor, the aroma of coffee: it all comes from the roasting process which releases a large number of chemicals from the tiny bean. In fact, the average cup of coffee contains more than 1,000 chemicals. To transfer those delicious chemicals to the hot water in our cup, we run water over those roasted beans. To increase our success, we both grind the beans to increase their surface area (and thus more exposure of those chemicals to the water) and heat the water since higher temperatures (and thus energies) speed up the removal of molecules from a solid.
Lucky for us coffee drinkers, smaller and more water soluble molecules like acids will get extracted first and those tend to be the tastier, less bitter flavors. Coffee drinkers are well aware that not every cup is created equal. I have rarely met a cup of coffee that I won’t drink (a little soy milk goes a long way) but I know others who won’t touch, say a gas station brew and insist upon espresso.
The difference lies not in the beans themselves but in the preparation. For espresso, the beans are very finely ground (almost to the texture of powdered sugar) and the brewing time is much shorter than for regular drip coffee. The way to decrease brewing time is to push the water through the ground coffee faster so espresso machines can reach up to 15 atmospheres of pressure to move a cup’s worth of water in less than 30 seconds.