How Espresso Works

By: Madeline Bullock  | 
Cup of cappucino
Espresso is a process of extracting the flavor from ground coffee beans by a combination of not-quite-boiling-hot water and pressure.

­In the early 1960s specialty coffee shops in the United States were virtually unknown, but today, in many U.S. cities, you see them everywhere. According to this article in Business Week Online, the well-known specialty coffee outlet Starbucks has grown from an initial 17 shops in Seattle in 1987 to well over 5,500 locations worldwide.

Today, you can buy an espresso almost anywhere, from specialty sit-down coffee shops to small drive-thru buildings or trailers. Lots of cafeterias, book stores and other establishments now offer espresso drinks and most malls have espresso carts or kiosks. There are many assorted flavors of syrups you can add and a multitude of different ways to enjoy your espresso. Latte, cappuccino, Americano… What is the fascination with these little cups of very strong coffee?


In this article, we'll examine what espresso is, and what factors are taken into consideration to make a "perfect" espresso consistently time after time.

What Is Espresso?

Simple camping-style espresso machine. When the water is heated over a fire, pressure builds inside the vessel, and the only way for it to escape is up the tube, through the coffee and out of the tube in the top. Since the end of the tube is under water, the pressure forces the hot water up through the tube.

­Espresso does not refer to a particular type of bean, but rather a process of extracting the flavor from ground coffee beans by a combination of not-quite-boiling-hot water and pressure. The word can also refer to the product resulting from this process -- as in "I'll have a cup of espresso, please."

Pronounced ess-press-o, not eX-press-o, espresso is an Italian word, shortened from caffè espresso. Although many people believe the word espresso is an adaptation or translation of Italian for "express"(as in "fast") because espresso is made and served immediately, that's not the case. It's actually the past participle of the word esprimere, which means, "to express" or "to press out." So caffè espresso literally means "pressed-out coffee." Espresso is generally attributed to originating in Italy around the 1900s, when Luigi Bezzera filed a patent for a machine that forced boiling water and steam through coffee grind into a cup.


In Italy, good espresso brewing is defined by "the four Ms:"

  • Miscela
  • Macinazione
  • Macchina
  • Mano

This loosely translates in English to:

  • Blend or mix of coffee beans
  • The grind or grinding process
  • The machine
  • The person making the espresso

In order to understand the espresso phenomenon, it's important to have an understanding of the espresso experience. Almost all espresso afficionados will tell you that flavor is key. The appreciation of a good cup of espresso is more about flavor, which is a melding of the aroma and taste of the espresso, rather than just the taste alone. To prove this to yourself, hold your nose the next time you drink espresso. You will taste the bitterness of the caffeine, but you will not experience the full flavor of the coffee, which is a characteristic of smell.

Let's take a closer look at the defining elements that can create the perfect espresso experience.



Espresso -- note the rich, reddish crema floating on top

Beans designated for espresso are roasted longer than regular coffee beans, so that the oils are brought to the surface of the bean. The selection of the best type of bean is open to debate, although Arabica beans are credited with providing the most balanced compromise between flavor, acidity and bitterness. Robusta beans, although attributed to being a lower quality bean, provide more crema (the reddish-golden creamy foam floating on the top of a perfect espresso), and make an excellent augmentation to Arabica beans.

Without crema, espresso is nothing but thick, strong coffee. The crema also slows the dispersion of the volatile oils into the air after brewing, contributing to the distinctive aroma of espresso.


For the best espresso, try to use the freshest beans. Old beans may appear very oily, and have a stale odor. You should always store your beans in an airtight container in a dark, dry place. Do not store beans in the freezer, as this will crystallize the moisture, and deteriorate the porous structure of the beans, which may result in a lower quality flavor.


Coffee beans (left) and ground coffee(right). The beans are ground very finely -- much finer than for drip coffee makers. Note that the consistency is almost like powdered sugar.

One espresso requires 7 to 9 grams (about ½ tablespoon) of ground coffee beans per 2 ounces (4 tablespoons) of water. This produces a 1.5 oz. shot of dark coffee concentrate possessing a strong, slightly bitter-sweet flavor and an almost syrupy consistency. Once ground, the oils in the coffee beans are exposed to air, beginning to oxidize and lose flavor almost immediately. This also affects crema. To ensure maximum flavor and aroma, beans should be ground as close to brewing as possible.

Espresso grind is much finer than regular brew coffee. Almost powder-like, yet slightly gritty, like the consistency of superfine sugar. This provides the proper resistance to the water being forced through it. It is generally agreed that blade grinders (the kind that, as a button is depressed, a blade rotates) produce a very poor quality grind, because they chop and pulverize the beans, rather than grind them. Burr grinders are better. Whether hand-crank or electric, a burr grinder slices the beans into controlled, sized pieces, optimizing the flavor extraction.


Inside a Burr Grinder
Photo Courtesy Sweet Maria's Coffee Roastery

After the proper amount of ground beans is measured or dosed, the grind is gently, but firmly packed into the gruppa, a metal cup with holes in the bottom. Next, the grounds should be tamped to evenly interlock the bean granules. Unless they are compacted, water will flow too quickly through the grounds making the resulting coffee too weak. There are quite a variety of tamping tools available. While most people prefer the flat bottom type, there are a few others that like the rounded bottom. Like so many other components to the fine art of espresso making, there is an optimum density of compactness to strive for; not too hard, not too soft, but just right. Finally, the key to proper grind is extraction time. With proper dose and tamp, one shot of espresso should optimally be extracted in 25-30 seconds.



Moka Pot
Photo Courtesy Sweet Maria's Coffee Roastery

There are two ways to make espresso, steam and pump. The steam models are the stovetop boilers and many countertop pressure units. The stovetop boilers, called Moka pots are fairly inexpensive, small, two part espresso pots. Widely used in Europe, they are considered inferior by many espresso connoisseurs today, because they produce a pretty bitter espresso. The higher temperature of the steam-driven, boiling-hot water that is forced through the grounds is the culprit. There is no crema, and the resulting product can sometimes have an almost burnt flavor. The countertop pressure machines are fairly lightweight and have a steam wand for frothing milk. These units produce an acceptable cup of espresso and are best for those folks who want espresso on an occasional to semi-regular basis.

Pump units are the types of machines used in espresso bars, and are the best investment for the true espresso addict. The water is kept at slightly below boiling temperature (approximately 192°F), with a buildup of steam pressure measured in atmospheres. The steam is then forced through the coffee grounds by hand or machine pumping. This produces the most consistent and flavorful espresso.


Espresso machines can range in cost from as little as $50 for a small Moka pot into the thousands of dollars for a top of the line pump model.


Espresso Machine
Photo Courtesy Sweet Maria's

An espresso is only as good as its maker. A conscientious espresso maker will strive to use the best beans, ground to the proper consistency in a good machine.

Cleanliness is a very important factor. Residue from old grinds will contaminate the flavor, producing a mediocre to lousy espresso. Grinders should be thoroughly cleaned at least weekly, using a stiff brush like a toothbrush or stiff bristle paintbrush to clean the grinding plates, and a clean soft rag to wipe down all parts. NEVER use water to clean an electric grinder! Espresso machines should be thoroughly cleaned daily, or immediately after use to prevent a buildup of oils that could affect flavor.


Ways to Enjoy Espresso

Cappuccino (left) and Espresso (right)

If straight-up espresso doesn't appeal to you, there are several other espresso drinks to try. Most establishments like to have a signature drink that only they produce, but there are some basic recipes that remain the same wherever you go:

  • Espresso: A strong, one and a half ounce shot of coffee served in a demitasse cup. After an initial sip of water to cleanse the palate, this is traditionally enjoyed with a light sprinkling of sugar on top, not breaking the crema surface, or served with a slice of lemon peel after a meal.
  • Ristretto: 1oz prepared, vs. 1.5oz for espresso.
  • Cappuccino: One third espresso, one third milk, one third milk foam, traditionally with a generous sprinkling of cocoa powder on top.
  • Latte: One-third espresso, two-thirds milk. For many Italians, this is a morning only event. According to Italian tradition -- no milk in your coffee past the noon hour.
  • Americano: Tastes like a cup of really strong coffee. An espresso shot with enough hot water to fill the cup.
  • Macchiato: Espresso shot with a small dollop of frothed milk.
  • Mocha: Latte with a spoonful of chocolate and whipped cream on top.
  • Fantasia: Mocha with swirl of flavored syrup.


Milk Matters

About espresso and milk: Milk can hide many sins of less-than-perfect espresso. Frothing milk correctly is a fine art in itself, with its own set of specifications. Basically, you don't want to heat the milk past about 150°F, almost too hot to touch in a metal container. The result you want is lots of foam at the top. This will take about 30-45 second for 6 ounces of milk (enough for 2 cappuccinos) with a steam wand, and a slight up and down motion of the container.

True espresso fanatics will roast their own beans, and debate about proper tamping pressure, crema criteria, proportions, desirability of mineral over distilled water, and the advantages of pump over steam methods. But you don't have to embrace the extremes in order to enjoy good espresso at home. The key to perfecting the art of espresso is PRACTICE! The more familiar you become with making and drinking espresso, the better.


For more information on espresso and related topics, check out the links on the next page.

Frequently Answered Questions

Is espresso just black coffee?
Espresso is a type of coffee that is made by forcing hot water through coffee grounds at high pressure. This results in a strong, concentrated coffee that has a slightly bitter flavor.