Note: First of all let’s get one thing straight, the word is “espresso,” not “expresso.”
In Italian “espresso” means “expressed,” as in “to press or squeeze out: to express the juice of grapes,” or in this case, to express the heart of the coffee bean into a small cup. The word “expresso” is an American bastardization of the word which implies speed, but which has no meaning in Italian.
This article is reproduced, mostly in tact, from one of my favorite coffee information sources, Coffee Research.org.
–Muggsy
A double espresso is a 47-62.5 mL (1.5-2 ounce) extract that is prepared from 14-17 grams of coffee through which purified water of 88-95°C has been forced at 9-10 atmospheres of pressure for a brew time of 22-28 seconds. The espresso should drip out of the porta-filter like warm honey, have a deep reddish-brown color, and a crema that makes up 10-30% of the beverage.
The best espresso should be extraordinarily sweet, have a potent aroma, and flavor similar to freshly ground coffee. The crema should be dark reddish-brown and smooth, yet thick. A perfect espresso should be enjoyable straight with no additives, yet bold enough to not disappear in milk. A pleasant and aromatic aftertaste should linger on the palate for several minutes after consumption.
The following steps describe in detail how to make espresso. You will also learn about the various factors and problems with espresso that limit its perfection. If any of these factors are off, you will not achieve a high quality espresso.
Making Perfect Espresso
Without a good espresso coffee blend you cannot have a good espresso. The best espresso coffee beans are blended to achieve the sweetness, aromatics, and smoothness desired in espresso. The espresso blend must also be fresh. We recommend using espresso within four days of roasting.
You can find great espresso at our online store! -ed.
Grinding Espresso
The grind must be continuously monitored throughout the day to achieve an extraction time of 25-30 seconds. Do not change the pressure you tamp with to compensate for a grind that has become too large or small. For more information, read the section about espresso grinding.
Espresso Grinder
A high quality burr grinder is essential for espresso. A conical burr grinder is preferred to flat burrs since the particle size is more even, they last longer, and the coffee is not heated during the grinding process. If the burrs become hot the coffee aroma will be diminished. A conical/parallel hybrid blade is considered the best design by many coffee professionals.
Dosing Espresso
Coffee must be freshly ground to achieve peak flavors. Grind and dose on demand. When someone orders an espresso grind only what is necessary for one shot, dose properly, tamp, and brew. Discard any espresso grounds that are not used within 30 seconds.
Distribution in Portafilter
Distribute the coffee evenly after dosing in the porta-filter before tamping.
Tamping Espresso
Tamp the coffee once very evenly with 5 lbs of pressure, then once with 30 lbs of pressure, and polish 720° with 20 lbs of pressure.
Water mineral content
The water used for espresso must be filtered. Some cities must even compensate for the mineral content of their water. Over time oxygen will be forced out of the water in the espresso machine leading to off tasting water. Try filling a small glass with water, letting it cool, and tasting it for off flavors. If the water tastes strange you may want to dump the tanks daily and begin with fresh water.
Water temperature
The water temperature should be stable and somewhere between 92-96°C. Choosing the best espresso machine is very important to both water temperature and temperature stability.
Temperature stabilizing
A stable temperature helps ensure that you prepare excellent espresso. For more information about stabilizing the temperature of your espresso machine, read about espresso temperature stabilizing.
Water pressure
The pressure of the water forced through the espresso should be between 9 and 10 atm. This pressure is responsible for the development of the crema.
Boiler pressure
The boiler pressure determines the amount of water to be incorporated in the steam. If your milk is not foaming correctly as described in the section on latte art, you may want to experiment with different boiler pressures. Boiler pressure, however, should only be altered by professionals. You can check your boiler pressure by looking at the boiler pressure gauge on the front of most espresso machines.
Extraction time
Extraction time to fill two 1-oz cups should be between 25-30 seconds. Despite the time the pump should be turned off if the espresso becomes slightly lighter in color. The goal is to have a dark red espresso take approximately 25-30 seconds to brew with no change in color. Fore more information, read the section on extracting espresso.
Timeliness
Act quickly, but carefully. You should spend no longer than 30 seconds for the time it takes to dose, distribute, tamp, pre-heat, and brew the espresso.
Espresso machine cleanliness
Coffee machine cleaning is probably the biggest problem with espresso today. If the machine, basket, and porta-filter are not cleaned regularly, the espresso will always taste rancid.
Espresso grinder maintenance
Everyday the burr blades should be swept clean. Between shots you may want to brush out the excess espresso that gets stuck between the burrs and the dosing chamber. The burrs must be replaced at least yearly so that they continue to produce coffee granules with a maximal surface area.
Espresso cup
The espresso cup should be pre-heated from a source other than the espresso machine. Filling a cup with water from the espresso machine prior to brewing the espresso will lower the temperature of the water in the boiler and the espresso extraction will be uneven. The espresso cup should have thick walls and a narrow mouth to retain heat and aroma, respectively.
Porta-filter and basket
The porta-filter should always remain the same temperature as the water used to brew the espresso. Therefore it should always remain in the group head. The basket should hold 16-18 grams of coffee and must be straight walled. Curvatures in the basket will lead to uneven extraction.
Environmental Factors
The humidity and temperature will change throughout the day. Since coffee is hydroscopic (absorbs moisture), the grind size must be changed throughout the day to achieve a brew time of 25-30 seconds. The temperature will not affect the espresso like the humidity, but it is important to avoid exposing the coffee to any high temperatures until brewing.
Practice makes perfect
If you want to learn to make espresso, it is essential to practice and experiment. The key to making espresso is to realize that it always has further potential. By changing any one of these factors you can improve or diminish its potential. Espresso preparation is an art that demands the precision and dedication of science. I have never achieved, nor have ever seen anyone make a perfect espresso. A perfect espresso is more of a concept than an actuality. The beauty is that espresso is volatile and difficult. If it were easy, we would develop a machine that knows how to make a perfect espresso every time. There are so many factors involved in espresso preparation that only a human mind and a passionate heart can begin to understand and control its complexity.
Reprinted from CoffeeResearch.org.