Espresso can be wildly delicious, but it takes a lot of effort. Practically any commercial coffee shop can produce one, but the art of espresso extraction is not a forgiving one, and many purveyors of this drink execute and serve espresso with significant taste faults. Great espresso is difficult to make because it is a very small, highly concentrated beverage, and as such the tolerances involved are extremely tight.
Consider that most double espressos are dose between 17-20 grams, which is roughly the amount need to produce 14 ounces of drip coffee. So the same acids and sugars and other solubles and other flavoring material are packed into such a smaller yield. The result is flavor amplification, which is a wonderful trait of espresso. But it also means that extraction problems are highly noticeable. The margin for error in espresso preparation is very small.
Defining Espresso
Simply put, espresso is a small, made-to-order, concentrated coffee that consists of liquid topped by crema.
Another way to define espresso is by its brewing method: pressurized infusion.
Pressurized infusion is simple one of several brewing methods (others include steeping, drip filtration, vacuum filtration and more). In this method, pressurized water of between 2 and 10 atmospheres of pressure is forced through the coffee grounds, which are compacted into a small cake in the brewing chamber. The combination of heat and force extracts soluble flavoring materials, emulsifies insoluble oils and suspends both ultra-fine bean fiber particles and gas bubbles. The result is a beverage with an extremely high solubles concentration. To produce a uniform beverage using pressurized infusion, rapid brewing times are necessary.
Four Phases of Espresso Extraction
From beginning to end, espresso changes throughout the brewing process. A good barista understands how and when espresso changes throughout extraction. These changes can be divided into four distinct phases.
Note: To understand these phases, pull a shot of espresso and catch the flow in a new cup every 10 seconds. Then sip and consider the product using the table below as a guide.
| Phase One (1-10 seconds) | Extraction starts slowly and this portion likely won’t yield much liquid. Initial liquid will appear dark, with a viscous and textured mouthfeel, intense, concentrated and somewhat muddled flavor characteristics. |
| Phase Two (10-20 seconds) | As flow starts to quicken, the extraction yields more liquid and color begins to lighten as the coffee develops more complexity, brightness (or, acidity) and sweetness. |
| Phase Three (20-30 seconds) | Flow continues at a quicker pace, and color continues to lighten. Sweetness is more dominant, and body is becoming lighter, although still somewhat viscous. |
| Phase Four (30-40 seconds) | Most or all of the coffee’s desired solids are gone at this point, and body is considerably thinner, like water. Color is light yellow or blonde and flavor is weakened and bitter. |
Consider phase four (30-40 seconds). Does that sound like an appealing drink? Nope. That is why all espresso extraction should occur within the initial three phases.
The Barista’s Role
When preparing espresso, a barista’s basic goals should be to:
- Create a dose of consistent mass every shot.
- Choose the grind setting that will provide the desired flow resistance.
- Distribute the dose evenly to provide uniform resistance to the water.
- Tamp with enough pressure to eliminate void spaces within the coffee bed and to seal the surface of the bed.
- Ensure the brewing water is of the desired temperature.
- Complete all of these tasks efficiently.
