How Does An Espresso Machine Work? Former Barista Explains

Published on 02/14/2024 · 9 min readDive into the mechanics of your morning brew! A former barista explains how an espresso machine works, from water heating to coffee extraction!
Ethan Hauck, Coffee Expert
By Coffee Expert Ethan Hauck

Photo by Rawpixel

No matter their design or marketing, espresso machines are often seen as intimidating to learn. While this can be true (to an extent), a proper espresso is just as much an art as fine dining: It requires passion, time, and — perhaps most importantly — a few mistakes along the way.

While this guide is here to smooth the process, it’s important to remember that this is a craft in which perfection won’t come easily. If you’re stuck, be sure to reach out to a Curated Coffee and Espresso Expert for personally tailored guidance from someone in the know.

What You’ll Need

Brewing an ideal cup of espresso requires high-quality beans that are ground to what I like to call the “Goldilocks zone” — not too fine and not too coarse, but just right. After that, you have to tamp and measure your coffee properly, fine-tune the extraction time, and get a feel for frothing milk (only if you want a creamy latte, cortado, or cappuccino, of course).

Now, let’s get into the nitty-gritty of how to use an espresso machine at home. First things first, we’ll need to gather our equipment. Namely, we’ll need a(n):

  1. Espresso tamper
  2. Portafilter
  3. Scale and bowl
  4. Water
  5. Coffee beans and an espresso grinder

While the espresso tamper, beans, and grinder are all personal to an extent, your water and portafilter are not. Ensure your espresso tamper and portafilter are the same size to allow a proper tamp and move to the next items. Each user’s water will vary by their location, though it’s best, as a general rule, to use filtered water. Even if the water in your home tests well, a filter removes any minerals or subtle flavors it’s picked up along the way.

The scale (the Zwilling Enfinigy is a solid budget choice) and bowl are simple; you’ll want to measure your coffee for two reasons. First, it ensures consistency when fine-tuning coffee. Second, and arguably more vital, this will be your starting point in learning what you specifically enjoy.

As for your coffee beans and espresso grinder, those are entirely up to you. While the industry standard is leaning further toward a medium roast (rather than dark) for espresso, that doesn’t really matter at home, does it? Whether you like a strong, ultra-dark roast or something on the lighter side, go for it! Just be sure to use a high-quality grinder like the Espressione Conical Burr grinder or Breville Smart Grinder Pro.

With our gear gathered, let’s make some espresso!

Steps in Using an Espresso Machine

1. Always Begin With Water and Heat

Specifically, preheat your machine, top up its water reservoir with filtered water, and pull a shot of just hot water through your portafilter to get it nice and toasty.

2. Measure and Grind Your Coffee

Most professionals advise around 8-9g for a single shot and around 20g for a double shot.

Photo by Antonio Diaz

3. Fill the Portafilter and Tamp Your Espresso

Using the proper tamping technique, apply an even, level 30lbs of pressure to your espresso.

Photo by Narong Khueankaew

4. Place the Portafilter in Your Espresso Machine

You’ll generally need to rotate your portafilter between 60-90° clockwise to insert and lock it into place with a counterclockwise motion. This will vary from machine to machine, so don’t be discouraged if it isn’t immediate.

Photo by Anastasia Ness

5. Pull Your Shot

Once again, the “how” of this will vary by your machine. Most will offer a knob (like the De’Longhi Stilosa), button/switch (such as the Rancilio Silvia Pro X), or LED touchscreen (see the De’Longhi Dinamica).

6. Optional: Foam Your Milk or Non-Dairy Alternative

If your machine has a milk frother, this process is extremely simple. If not, you’ll need something separate — I personally love the De’Longhi Milk Frother, but that’s up to you.

Photo by Antonio Diaz

How Does an Espresso Machine Work?

This is a shockingly complicated answer. The extremely short answer is that espresso machines use a combination of densely compacted ground coffee and high-pressure water to better extract your coffee’s natural oils, resulting in a more full-bodied, smooth mouthfeel. This leads to the crema that makes espresso so beloved — but that’s just the beginning.

Before we dive too deep, let’s cover the basics. Whether you’re using a fully manual (“old-school”) espresso maker like the Flair Pro 2 or a super-automatic such as the De’Longhi Dinamica, there are several common requirements for an espresso machine to work properly. Four simple parts make up the majority of espresso machines:

  1. Water Tank (AKA Water Reservoir)
    1. This is where your water lives when not in use. Since all coffee needs water, this is a vital part of every machine.
  2. Pump
    1. The pump does precisely what its name hints at — it pumps water from the reservoir to the boiler, and from the boiler to the group head. Without a properly functioning pump, you will be unable to make espresso.
  3. Boiler
    1. Like the pump, the boiler’s job is incredibly simple yet integral to your machine’s operation. This is where your water will heat both for extraction and for the steam wand. Some machines use a single boiler, others use a double boiler, and others still will use a heat exchange or Thermoblock boiler. Each functions in a different way but ultimately provides the same service.
  4. Group Head
    1. This is where everything comes together, hence the term “head.” In practice, the group head is where your hot, pressurized water meets the portafilter. This means that it’s also often the first part to need repairs, as there are several (usually four) points at which it can fail: the portafilter lock, the water channel, the pump connection, and the gaskets throughout.

While the reservoir, pump, boiler, and group head are crucial to your espresso machine functioning properly, the true heroes of the show are the three below.

High-Pressure, Near-Boiling Water

When shopping for an espresso machine, it’s common to see them sold as a 15-bar, 19-bar, and so on — but that term, “bar,” is actually quite important.

The measurement of one bar is equal to the Earth’s current atmospheric pressure (ie, a lot of pressure). Most professional baristas use higher-pressure machines, whereas most at-home espresso machines use machines with a maximum pressure of 15 bars. It’s also important to note that the stated pressure on your machine, let’s say 15 bars for ease of reference, is often not the actual amount of pressure used when pulling espresso. Regularly, espresso machines will output roughly one-half to two-thirds of their maximum pressure.

This is because of two things: first, “ideal” espresso requires right around 130 PSI, and 15 bars of pressure is nearly 220 PSI — far more than we need. Second, and arguably of more importance, are your beans. More specifically, how fine or coarse they’re ground will directly impact the speed with which your now super-pressurized water can travel through the grounds, which brings us to the next point.

Coffee Beans and Grind Size

We all know that coffee requires beans. But it’s nowhere nearly as well-known that one’s grind is just as important as the quality of their beans and the roast.

This is because espresso (literally “pressed-out coffee” in Italian) requires the perfect balance of hot water, high pressure, and an extremely condensed “puck” of coffee grounds. A coarser grind will cause the water to flow far faster through the grounds, reducing the quality of your extraction. This results in a watery espresso (if you can call it that) which is more akin to an Americano or classic drip coffee.

Conversely, too fine of a grind will result in your shots of espresso having a fine layer of sediment at the bottom (not ideal). While the water will find its way through the grinds properly, it will be met with too much resistance, leading to a more sour, over-extracted final product. The perfect middle ground of this conundrum will allow your water to pass through with some resistance without holding up the process.

To best explain what the proper grind does, I find that building an image is quite handy, so follow along:

You have to filter some water; while you don’t have proper filters (or anything to make one), what you do have is a collection of larger rocks, gravel, and sand. Assuming that you know these are magical, food-safe rocks and sand, which would you pick to filter the water? The larger rocks would leave big gaps of air, allowing the water to simply pass them by. Similarly, the gravel limits the size of any air pocket, but the gaps are still there. With sand, though, there is nearly no space between individual grains.

The same idea applies to coffee grounds. We’re trying to force the water through the coffee grounds — that means there can be no pockets of air or loosely packed sections. It all needs to be uniform, even, and highly condensed.

And that brings us to the last shared link in how an espresso machine works — the tamp.

The Tamp

Properly tamped espresso is the perfect espresso; the role that tamping plays is to bring together your water and coffee to make the delicious nectar that we all know and love.

By condensing the coffee grounds before extraction, the combination of high pressure and heat creates an emulsion (a mix or blend) of the coffee’s natural oils, resulting in the smooth, velvety texture of espresso. Applying thirty pounds of pressure to your grounds (now a puck) with a tamp will minimize the space between grounds, remove air pockets, and ensure that everything — quite literally — goes smoothly.

Final Word

Learning how to use an espresso machine can be … a lot. There are multiple moving parts in each machine, and getting to know the ins and outs of a specific model can prove quite challenging. However, understanding how and why the machine works can cut down on a lot of the struggle.

While this is an excellent starting point for those who are interested in learning to make espresso, the truth is that each espresso machine is different. While they’ll share the same general parts, techniques, and ingredients, sometimes the only answer is to spend the time to learn your machine. If you find yourself stuck, reach out to a Curated Expert. We’re here, for free, to share what we know and make sure you can get unstuck — so take advantage!

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