This article is the first of a series of articles about espresso preparation. Espresso has the potential to be the ultimate form of coffee, but is too often sour, bitter, and overpowering. To prepare espresso properly a number of factors must be monitored. The espresso must be freshly roasted, freshly ground with a sharp conical burr grinder, properly dosed and distributed, tamped correctly, and monitored closely during extraction. If done correctly the resulting espresso will be smoother, more aromatic, and more flavorful. The crema will be darker and thicker and the bitterness will be minimized. This article will focus on the grinding, dosing, and tamping of the espresso. Future articles will describe espresso extraction, latte art, roasting, and blending.
To extract espresso properly it is essential to use a burr grinder and to grind per order. The two major types of burrs used are flat and conical. Conical burrs are desirable because they increase the surface area of each coffee particle and the amount of flavor that can be extracted from the coffee. Since conical burrs have longer cutting edges, the burrs can rotate at a lower speed, which reduces the heat created. Flat burrs should be replaced after a total of 600 pounds of coffee has been ground and conical burrs should be replaced after a total of 2000 pounds of coffee has been ground. Espresso quality burr grinders can range in price from $500-$5,000.
Espresso is ground to a size in which the extraction process takes 23-28 seconds. It is important to only adjust the grind and not the pressure one tamps with to control the flow rate. In addition to particle size, the humidity plays a dramatic role on extraction time. Since coffee is hydroscopic, it absorbs moisture from the air causing a tighter pack and longer extraction time. Thus, the grind setting must be changed slightly throughout the day as the barista perceives changes in extraction time.
Coffee is freshest immediately after it is ground. After grinding the volatile oils that were previously protected inside the bean are exposed to the air, which oxidize and stale the coffee. This effect occurs immediately after grinding so it is important to tamp and extract the espresso as quickly as possible. The grinder should be activated for 15-20 seconds every time a shot is desired so that only freshly ground coffee is used.
While grinding, preheat and warm the group head by turning on the pump for several seconds. Remove the porta-filter, dump out the espresso, and wipe the basket dry with a clean towel. Wiping the basket dry will prevent water from finding a path of least resistance and will help ensure an even extraction. To dose the freshly ground coffee the barista should pull several times until the entire basket is filled with ground coffee. To reduce wasting coffee use a timer to determine how long you must let the grinder run to fill the basket.
Tamping Step By Step
Now that the coffee has been dosed properly the barista must tamp the coffee to prepare a tight pellet of espresso. It is important to remember that water under pressure in the porta-filter will try to find the easiest way out. If the espresso is unevenly tamped, loose, or jostled during the tamping or extraction procedure the espresso will be unevenly extracted. Tamping is one of the easier methods of espresso preparation to master and a properly tamped coffee will improve quality considerably.
After the ground coffee has been dosed into the porta-filter it is unevenly distributed. It is necessary to take hold of the porta-filter in one hand while using the other hand to quickly, but gently, level the coffee. This is usually accomplished by pulling the coffee to one side of the basket with a slightly curled pinky finger, then pushing the coffee back to the opposite side of the basket. The key is to evenly distribute the coffee without pressing into the grounds or leaving any empty space on the sides of the basket.
Once you are done distributing the grounds it is time for the first tamp. Without moving the porta-filter, hold the tamper so that the base of the handle fits into the palm of your hand. Your wrist should be straight, and the tamper should be a straight extension of your arm. Press gently on the coffee with five pounds of pressure. You will notice that some of the grounds will stick to the side of the basket. Therefore, you must gently tap the basket with the handle on the portafilter to knock the grounds onto the flat pellet you just formed.**
EDITOR UPDATE: This has become a highly debated point, but the trend has moved away from the side tap. Just brush the loose grounds off by hand.
The next step is to apply the finishing tamp. The shape of the pellet has already been formed, and the finishing tamp confirms this impression. With the tamper held as before, press on the pellet with exactly thirty pounds of pressure. It is useful to tamp on a bathroom scale until you become comfortable with the amount of force necessary to achieve the appropriate pressure. After tamping turn the tamper 720° to polish the surface.
Make sure you tamp evenly. An uneven tamp will result in an uneven extraction.
The above steps should be carried out in about twenty seconds. Although speed is important, it is necessary to be careful not to bump the basket during this process. Sharply hitting the basket will unevenly distribute the grounds allowing shortcuts for the water to pass through. If there are any weak spots or holes in the espresso pellet the water will push through this area, over extracting this portion of coffee while under extracting the rest of the pellet. Improper tamping will result in a twirling pour or white crema.
The use of the proper tamper is essential. The first action you should take is to throw away the plastic round bottom tamper that you currently have. The tamper should be made of aluminum or similar light metal and should have a diameter so that it fits firmly into the basket. Marzocco baskets are 58mm, so order the appropriate size. Without a flat packing surface you create indents which cause uneven extraction.