If you are interested in perfecting your espresso making skills and technique, you need to understand the science behind it. (the SCA-standard 9-bar espresso definition) The science behind espresso brewing is called extraction.
Coffee extraction is the process of dissolving ground coffee in water. This chemistry concept is crucial in coffee brewing because it determines the quality of your coffee, as emphasized by the Specialty Coffee Association.
Pulling an espresso shot with a Gaggia Carezza espresso machine.[/caption]