Every Barista has their own opinion as to what makes a perfect shop of espresso.  But in the end, it all comes down to the taste.  Basically, there are 6 things that contribute to and affect a shot of espresso.  The Coffee Beans, the Coffee Grind, Dose, Tamp, Water Temperature and the Pour.  Certainly, the espresso machine itself is ultimately important as it must be able to achieve the desired espresso brewing process.

While preference for coffee flavor is as individual as the baristas themselves, freshly roasted coffee beans certainly give the best flavor.  Arabica coffee beans are recommended and used mostly.

A very fine coffee grind is highly recommended to ensure quality taste, regardless of the selection of coffee bean.  The finer the grind the more coffee flavor is extracted.

The proper dose for 1 shot of espresso should be between 7 - 9 grams of coffee and double that dose for a double shot.

Generally, a 1 oz shot is considered the median and is most often recommended although, there are those who prefer 1 1/4 to 1 1/2 ounce shots.

Again, since personal preference dictates the espresso brewing time varies from 24 to 30 seconds with 28 - 30 being considered excellent timing.

Proper tamping is done adding 30 - 40 pounds of pressure to the coffee grinds in the portafilter.  The grinds must be even and leveled out which can be ensured by keeping your elbow at 90 degrees.

The water temperature should be anywhere from 195 to 200 degrees F. although there are some baristas that insist that the temperature be as high as 203 degrees F.

The preferred range of water pressure for great espresso extraction is 8 - 10 bars which generates 140 pounds per square inch.  Some baristas set their machine to lower levels to minimize the extraction of any unpleasant coffee oils.

Driving out the oils from the coffee grounds is what actually creates a proper espresso shot.  Forcing out water at 140 pounds per square inch can only be done using an Espresso Machine.  If the oils are not extracted properly, you will succeed in simply brewing coffee.

Crema is the sign of a proper espresso.  Crema attaches to our taste buds and produces a long after-taste.  The espresso shot must come out of the machine like warm honey.  You will notice the crema pour at the top of an espresso shot.

In order to achieve the perfect espresso shot each piece of equipment may require further alteration in the water temperature or the dose of coffee.  This all depends on the age, model, level of maintenance, and wear and tear that the espresso machine has endured.