How Does an Espresso Machine Work?

How Does an Espresso Machine Work?

Richly aromatic, highly-concentrated, extra-viscous coffee with delicious crema on top. Nothing quite compares to a freshly-brewed cup of espresso!

Developed in Italy in the late 1800s, espresso is the most common form of coffee found in Southern Europe. It has enjoyed widespread popularity across the rest of the world with the rise of home espresso machines

Moreover, espresso is a core element of several popular coffee beverages, including cappuccinos, macchiatos, lattes, flat whites, and Americanos. These machines are capable of making our favorite java beverages all in a matter of seconds.

Have you ever wondered how an espresso machine works to create these delectable beverages? You're not alone. For instance: 

  • Why does it take such a comparatively large device to produce such a small cup of coffee? 
  • What steps are involved in brewing espresso?
  • What are the various parts that make up the machine's inner workings?
  • What role does each part play? 

While the myriad of tubes and softly whirring parts on the inside and outside of most espresso machines might seem too complicated to comprehend, the truth is that understanding how an espresso machine works is easy once you break it down into steps.

Keep reading for a full run-down of how an espresso machine works, from the individual parts inside most machines to how those parts work together to meet your caffeine needs each morning.

The Short Answer

Before we get into the specifics, let's briefly summarize how an espresso machine works. A better understanding of the basic process of brewing espresso will help you gain a greater appreciation for the role and function of each part within the machine. 

All espresso machines, regardless of their complexity, require a water source and a heat source to brew espresso. They also require a hardened, tamped-down “puck” of finely ground coffee beans. Finally, all espresso machines need a reservoir to store the finished espresso or a nozzle through which the espresso can drip into a waiting cup. 

In the most basic terms, an espresso machine works by using steam, pistons, or pumps to force hot water through the puck of coffee beans. The high pressure inside an espresso machine and the low water ratio to coffee give espresso its distinctive thick consistency. Higher-end and more expensive espresso machines may have additional features that contribute to the overall flavor profile of the beverage. 

Now that we've set the scene and de-mystified the baffling complexity of espresso machines (somewhat), are you ready to dive a little deeper? Let's move on toward a more complete understanding of how an espresso machine works by covering the various forms and functions in greater detail.

What are the Differences Between an Automatic and Semi-Automatic Espresso Machine?

In researching how an espresso machine works, you may have come across two distinct categories of espresso machines: automatic and semi-automatic.

Most pump-driven espresso machines use sensors, valves, and grinders to complete the brewing process with little to no manual effort. They are therefore referred to collectively as automatic espresso machines. Within this category are several subclasses of automation: 

Semi-automatic

Semi-automatic machines include the most basic pump-driven models. These use an electric pump rather than manual force to send the water through the machine, releasing any leftover pressure using a three-way valve. The brewer is still responsible for grinding and compressing the coffee and determining how much water to put into the machine and how long the brew time should be.

Automatic

Automatic espresso machines differ from semi-automatic machines in that they also automate the volume and brew time. This level of automation is accomplished by adding a flowmeter to the group head, which is the faucet-like device the espresso passes through on its way into your cup. When the flowmeter detects that the desired amount of water has passed through, it sends a signal to the pump to turn off.

Super-automatic

The super automatic espresso machine carries automation one step further by incorporating elements that automatically grind and tamp down the coffee beans before extracting your perfectly-measured shot of espresso. Some super-automatic models can also automatically froth and dispense milk for more complex beverages like lattes and cappuccinos. 

The only responsibility you have as the brewer when using a super-automatic machine is to load the beans into the grinder and occasionally empty the compartment that contains the used-up grounds.

The Five Main Parts of a Pump-Driven Espresso Machine

Both commercial cafés and home espresso setups most commonly utilize the pump-driven model, meaning this type of espresso machine is the one you're most likely to encounter. Although pump-driven devices come in a wide variety of shapes, sizes, and levels of automation, certain elements are common to all of them.

Let's take a step-by-step look at the various features and functions that come together to explain how an espresso machine works. Here are the main components you want to familiarize yourself with: 

1. The Water Source

Since espresso is made of two simple ingredients, water and coffee, it follows that all espresso machines must have some water source. Some machines have water chambers that need to be filled manually each time you brew espresso, while other machines can hook up directly to your home or business's plumbing system through a water line. No matter which method is used, it's obvious that water is a key element of how an espresso machine works.

There are advantages and disadvantages to both types of water source. For instance, direct water lines streamline the brewing process and give you less work to do. However, manually filling the chamber means you can use filtered water instead of whatever comes out of your tap, leading to more control over the taste and overall quality of the espresso. 

Most commercial machines use direct water lines for greater convenience, while many home machines favor the use of manually-filled reservoirs as their water source. Home espresso makers often prefer to filter their water to remove the taste of chlorine and other water treatment methods used by most cities. While considered safe to drink in the amounts in which it's usually present in drinking water, chlorine can have a noticeable and negative effect on the flavor of a finished cup of espresso.

Some espresso machines give you the best of both worlds by utilizing water reservoirs and direct water lines. This lets you decide which type of water source you would like to use, depending on your specific needs. These flexible models are referred to as hybrids.

2. The Pump

You can think of the pump as the heart of your espresso machine since its job is to circulate water through the machine in the same way your heart pumps blood throughout your body. Two types of electric pumps are used in most pump-driven espresso machines: vibratory and rotary vein pumps.

The vibratory pump design uses an electromagnet to move a piston back and forth at an astonishing rate of nearly sixty pushes per second. The piston then pushes the water into the grounds at the roughly 130 psi necessary to create a perfect cup of espresso.

Rotary vein pumps are mechanical rather than electromagnetic. In this pump design, a spinning, motorized disk presses several tubes (called “veins”) into the sides of a chamber, creating pressure that then pushes water through the machine.

Both types of pumps are highly effective, with vibratory pumps being less expensive and rotary vein pumps providing more consistent pressure. Vibratory pumps may need extra maintenance over time, and rotary vein pumps are often found in larger machines that may take up too much counter space.

3. The Boiler

By this point in your journey into discovering how an espresso machine works, you've probably deduced that heat is a necessary component. All devices must incorporate a boiler to heat the water and steam to their necessary temperatures. Whereas simple stove top machines can be placed directly on top of your burner, pump machines utilize an electric heating element as part of their boiler systems.

Home espresso machines can have four different types of boilers, each with its own unique abbreviation for easy reference. In order from simplest to most complex, the categories are:

SB and SB/DU boilers are typically found in the simplest, least expensive pump-driven machines, while HX and DB or DH machines tend to be more expensive and provide a higher-quality product.

The other way in which boilers differ from one another is the method by which the machines determine their desired temperatures. The simplest machines use a device called a pressure stat, automatically calibrated to a certain temperature and cannot be reset to accommodate outside factors. Pressure stats are found in the least complex models and often struggle to produce consistent results over time.

More intricate boiler systems use digital temperature controls or proportional-integral-derivative controllers to give brewers more control over the temperature of the water. These devices are miniature computers that connect to the heat source and a temperature probe within the boiler. The computers can then receive continuous information about the exact heat of the water at any given moment, allowing them to cycle the heat source on and off as necessary to adhere to a pre programmed algorithm and ensure the water remains at a perfect temperature for brewing espresso.

4. The Steam Wand or Steam Chamber

While straight espresso is the caffeinated drink of choice across much of Europe, Americans tend to prefer espresso drinks that incorporate steamed milk in various quantities. This means that commercial and home espresso machines commonly utilize an element such as a steam wand that allows the user to create the heated, textured milk used in drinks such as lattes, flat whites, and cappuccinos.

Although steam wands are not integral to how an espresso machine works, they are nevertheless an important part of creating the ideal concentrated coffee beverage for many people around the world.

Steam wands can be purchased as add-ons to single-boiler and single boiler dual-use machines, though the steam wand cannot be used while the machine is brewing espresso. The more complex models, such as dual boiler and dual heater machines, come with one boiler for water and one boiler for steam, with a built-in steam wand protruding from the steam boiler.

5. The Group Head

The final element of how an espresso machine works is the group head, a collection of nozzles and valves the water passes through on its way to becoming espresso. There are four major components to any group head design:

  • The portafilter
  • The place where the portafilter locks in
  • The area for turning on the pump
  • A channel for the water to move from the boiler to the portafilter

Additionally, there are three major types of group heads: the E61, saturated, and semi-saturated models.

E61

In the E61 group head, the water leaves the boiler chamber and passes into the first area of the group head, called the filter chamber. Next, the water travels through a nozzle into the brewing channel. 

At this point, the water flow diverges into two paths: one that goes up and into the waiting coffee grounds and one that travels down into the pre-infusion chamber. This stage gives the coffee time to stabilize with the hot water before the pump turns on and introduces pressure into the brewing process.

As water moves through the system, it gradually flips the brew lever into the “up” position. At this point, the pump activates and starts to push pressurized water through the machine. The pre-infusion valve seals so that the only pathway for the water to travel is through the ground coffee.

When the brewing cycle is finished, the lever flips back into the “down” position and the pump turns off.

Saturated and Semi-Saturated

Saturated and semi-saturated group heads differ from the E61 in that the group head has direct access to the boiler, causing it to heat up much more quickly. They are also operated by tiny internal computers, while E61 group heads are largely mechanically-operated. Saturated group heads are open to the boiler, while semi-saturated heads include an area above the dispersion block that is separated from the boiler.

What are the Different Roles of the Parts in an Espresso Machine?

Each specific part plays an important role in how an espresso machine works. They're each vital to the overall quality and flavor of the end result. Carefully cleaning and maintaining your device will prolong the machine's life and ensure that each cup of espresso tastes exactly as it should.

For instance, if the water line or tank isn't kept clean, it could grow mold, adversely affecting the flavor of your coffee and your health.

The pump is the most complex moving part in most home espresso machines, so it often needs the most maintenance. Vibratory pumps are particularly prone to wear and tear and may even need to be replaced after a few years of use. The pump is an integral part of how an espresso machine works and if the pump breaks down, the water won't be able to move throughout the machine.

The steam wand also needs to be cleaned regularly, which may involve detaching your wand from the machine and cleaning out the tube it attaches to. Your steam wand is responsible for heating up and frothing milk to go into various espresso beverages. It should be cleaned thoroughly after each use to prevent bacteria from multiplying. Studies have shown that dairy-loving bacteria can flourish in temperatures as high as 50 degrees Celsius. Hence, a warm steam wand with milk residue is a prime breeding ground for disease-causing microbes.

Finally, the group head should also be kept clean since its role as the main pathway for water through the machine means its various parts and channels come into contact with your espresso throughout the brewing process. Even if every other part of your machine functions perfectly, your espresso could have a bitter flavor if the group head isn't properly cleaned.

In Conclusion

After glancing over the intricate and complex parts often involved in creating that perfect cup of espresso, it's only natural to wonder how an espresso machine works. If you're used to using a standard drip coffee machine or French press in your home, you may be overwhelmed by all the tubes and tunnels incorporated in an espresso machine.

Fortunately, how an espresso machine works is easily understood once you break these complicated devices down into their specific parts. Learning the specifics of how complex devices function is a rewarding experience, and often enhances our enjoyment of the products those devices provide. 

Now that you're armed with a greater understanding of how an espresso machine works, you'll be better able to determine which model is right for you if you ever want to get into home espresso brewing yourself. Happy brewing!