Espresso is created using a process called extraction, during which hot water is forced under pressure through a compressed cake of ground coffee.
The entire espresso machine, with the exception of the steam wands, is designed to facilitate this process.
The dispersion screen spreads water evenly over the top of the espresso cake, and pressure forces the water to permeate the coffee cake and extract soluble material from the ground coffee.
The espresso then exits small holes at the bottom of the portafilter basket, into a waiting receptacle.
Only so much desirable flavor is available in coffee, and if this extraction goes on too long or forces too much water through the coffee, undesirable compounds will be extracted into the beverage.
For this reason, amount of water and extraction time are strictly controlled by the barista.
Because this process happens under pressure, it is crucial that the coffee is compressed evenly within the portafilter basket.
This even packing helps prevent uneven extraction.
To achieve this, the barista performs an operation known as "tamping," using a specialized, hand-held piston to "tamp" the coffee into the portafilter.
PROCESS In order to make proper espresso, a specific, regular procedure must always be followed.
Each step performs an important function, and each is crucial to creating great tasting espresso.
The 12 steps are:

1. Preheat the ceramic cup by rinsing or soaking.
   
2. Remove portafilter from group head and dry portafilter basket.
   
3. Fill the espresso basket with fresh ground coffee from the grinder; grind only what you need to avoid waste! (Dose coffee into basket using 'sprinkler' arm technique to aid even coffee distribution)
4. Using quadrant distribution technique, distribute the ground coffee evenly within the basket and eliminate excess grounds.
   (With practice, 'excess' grounds should be minimized to control waste.
   )
5. Tamp the grounds firmly using quadrant tamping technique and wipe the top edge of the basket clean
6. Flush grouphead for 3 seconds to regulate temperature and eliminate used grounds
7. Insert the portafilter into the group head of the espresso machine
8. Immediately start the pump on the espresso machine
9. Observe the flow for quality characteristics of espresso (5 signs; see below)
10. Serve the espresso immediately, or use it to make the required beverage within 10 seconds.
    
11. Unfix the portafilter and knock out the spent grounds into the knockout box.
    
12. Rinse or wipe the portafilter clean and reaffix it into the grouphead so that it will stay hot.
    

THE 5 SIGNS OF PROPER EXTRACTION

1. Time - A proper shot should pull between 20-30 seconds.
   Slower or longer extractions will likely taste 'off,' so if a shot time falls outside this window, the grind must be adjusted.
   
2. Pour - When the shot is being extracted, the flow should start off slowly streaking, then become fuller and lighter in color while jumping slightly as it extracts.
   It should look like molasses as it pours - a slightly interrupted flow that is neither too thick (like a pencil), or too thin (like a needle).
   
3. Crema - Crema is a sweet, buttery substance that forms on the top of a shot, and is one of the sure signs of a properly extracted shot.
   It resembles the foamy head of a freshly pulled draft beer.
   
4. Color - extraction should start slowly, first appearing with streaking and darker color, and then become fuller and lighter as extraction proceeds and crema is produced.
   There should be both dark and light colors intermingling within the crema; it should exhibit reddish tones, or speckling, across the surface.
   
5. Taste - Above, all, the final analysis is ultimately dependent on taste.
   The espresso should taste slightly sweet and smoky, very robust and multi-dimensional.