To many, an espresso machine is simply a box that combines water and ground coffee to make a delicious shot. If that sounds like you then you may be looking to learn more about what’s actually happening under the hood of an espresso machine. Whether you’re trying to prevent watery, sour shots, or just interested to understand what separates espresso from other options on the cafe menu, we’ve got you covered!
In This Article
The Short Answer: How an Espresso Machine Works
The short and sweet answer to the question “how do espresso machines work” is that they use high pressure from a pump (usually 9 bars) to push coffee-temp water (195–205°F) through a puck of finely ground coffee beans. The result is a much more concentrated liquid than what you get with a drip, pour over, or press brew. This process also causes oils to emulsify and create a thin layer of crema on top, something you’ve probably seen if you’ve ever ordered a straight shot of espresso. Because an espresso machine has to heat its water and push it through a puck of espresso at pressure, it needs extra parts that a drip brewer just doesn’t. Espresso machines also need to be robust enough to stand up to the higher pressure that they require. This is why these machines tend to be more expensive than a drip brewer, and it's why a stovetop “espresso” maker isn’t quite on the level with a real espresso machine. With all of that said, most espresso machines, whether they’re a few hundred or a few thousand dollars, perform the same core function. What separates them is their component quality, degree of control, and extra features.
Espresso Machine Parts Explained
The Water System: Reservoir (or Line) + Pump
The start of the water’s journey to becoming espresso is in the reservoir (or water line, if it’s plumbed in). Water from the reservoir is drawn into the boiler, then pumped through the rest of the machine. This means that the pump is one of the two most important parts of an espresso machine. Without those 9 bars of pressure that the pump delivers, you wouldn’t have any espresso! This is also why it is so important to properly filter your water, as water that’s too hard can damage pump components after thousands of shots.
The Heating System: Boilers and Temperature Control
The other most important part of an espresso machine is the boiler. This is the component that heats water to temperature for brewing, and often heats and pressurizes steam for a steam wand. The trickiest thing about boilers is that they have to actually regulate and control the water temperature, as boiling water is too hot for brewing coffee. Some boilers do this with a simple thermostat, which often leads to fluctuations in temperature as the system chases the right temps. Higher quality machines use what’s called a PID controller - a control board that algorithmically operates the heating element in order to maintain a stable temperature. A bonus of these types of controllers is that they are usually adjustable, giving you the ability to select a temperature. Beyond control type, there’s also several different kinds of boilers. There’s standard single boilers, heat exchangers (which allow for simultaneous steaming and brewing), and dual boilers (one for steaming, one for brewing). Many modern machines even use thermoblocks or other types of heaters to flash heat water rather than have it sit in a traditional boiler. You don’t need to become an expert on this technology to understand that this is the part of the machine that heats up the water, and controls its temperature!
Related: Comparison: Heat Exchangers vs. Dual Boilers — a closer look at the two boiler setups most home enthusiasts end up choosing between.
Shop: Browse machines by boiler type in our full espresso machine collection.
The Brew Group: Group Head + Portafilter
The brew group is the point where the hot water leaves the machine and enters the portafilter (and thereby the coffee grounds). The portafilter is the metal basket with a handle that you grind and tamp coffee. Different levels of machine have different kinds of group heads. Some are heated, to help with temperature stability. Others use different methods to better disperse water evenly around the puck of coffee. This is also the point at which pre-infusion comes into play. This is the practice of wetting the puck at low pressure before brewing, giving the coffee a chance to bloom before the full pressure hits. This can lead to better extraction, and is a setting on many higher-end machines. Ultimately, this is the point where the water heated by the boiler and pumped at pressure through the group head meets the ground coffee - the magical moment where espresso happens!
The Steam Wand
A steam wand guides steam from the boiler (whether a single boiler on a steam setting, heat exchanger, or service boiler in a dual-boiler machine) into a pitcher to steam milk. While steaming technique is something we cover in other articles, the key thing to know here is that the steam wand is generally a simple component on cheaper machines. As you climb in price, you might find steam wands that are insulated to remain cool to the touch, and some that offer automated steaming. The most important thing to remember about steam wands is turning them off creates negative pressure that will suck a tiny bit of milk back up from the pitcher. This is why it’s very important to turn the wand on for a second after removing it from the milk to purge it!
Related: How to steam milk like a barista — our full walkthrough on texturing milk for lattes, cappuccinos, and flat whites.
What Happens When You Pull a Shot (Start to Finish)
To prepare coffee for espresso you must dose it, grind it on a powdery-fine setting, add it to your portafilter, then tamp. This process is often referred to as “puck prep,” and can also involve other accessories as you get deeper into the hobby. After puck prep, you’ll lock the portafilter into the group head of the espresso machine, then flip on the brew unit with the paddle, button, or lever. When you do this, water that’s been heated in the boiler is pumped through the machine and out of the group head at 9 bars of pressure. When this pressurized water meets the espresso, the tamped, tightly packed puck produces backpressure, and the water pressing through the puck picks up a syrupy consistency as it leaves the bottom of the portafilter. The result is the thick, sweet coffee known as espresso. Typically, all of this happens under a minute, with an ideal shot time generally being 25-30 seconds. It’s pretty impressive to see it all come together!
Types of Espresso Machines (and How They Change the Process)
Manual / Lever Machines
Manual espresso machines forego the pump and use a lever that the user controls to directly generate pressure. These machines require precision on the user side, and have a bit of a learning curve. We recommend these types of machines for existing hobbyists who want maximum control.
Semi-Automatic Machines
Semi-automatic machines are likely what you think of when you think of a classic espresso machine. The “semi” part of semi-automatic is the pump. The user still controls the machine directly, but instead of manually generating pressure the pump handles it. We recommend these types of machines for any user that wants control and the ability to learn about the hobby as they gain proficiency with their chosen machine.
Breville Bambino Plus Espresso Machine
A compact thermocoil machine that heats up in seconds, includes low-pressure pre-infusion, and pairs a real steam wand with an automatic frothing mode. It's the least intimidating way to see everything in this article happen on your own counter.
Best for first-time espresso makers who want café drinks without a long warm-up or a steep learning curve.
Diletta Bello Espresso Machine
A hand-built heat exchanger with a classic E61 group head, so you can brew and steam at the same time. Deliberately manual controls put shot and steam quality in your hands, which is exactly the kind of machine this article's water journey describes.
Best for the enthusiast who wants a traditional, do-it-yourself espresso experience that will last for years.
LELIT Bianca Espresso Machine
Dual boilers with PID temperature control, an E61 group, and a flow control paddle that lets you shape pressure and pre-infusion by hand mid-shot. It's every lever this article talks about, all adjustable.
Best for the home barista who wants to dial in every variable and chase the purest possible shot.
Shop: Shop semi-automatic espresso machines — the full lineup, sortable by price and boiler type.
Super-Automatic (Bean-to-Cup) Machines
Super-automatic espresso machines do it all for you, dosing, grinding, tamping, and pulling shots. Many even steam milk for you too! These machines are precisely engineered to pull a certain kind of shot, and while higher-end machines offer a wide range of programming options, you’ll never quite reach the level of precision and control that you get from a semi-automatic machine on a superauto. With that said, these machines often produce some great coffee, and have a much easier to handle learning curve. A good pick for the user who wants a cafe on their countertop without needing to learn the techniques of a pro barista.
Not sure which type fits you? Read Semi-Automatic vs. Superautomatic Espresso Machines for an honest breakdown of control versus convenience.
Keeping Your Espresso Machine Working
One of the most important parts of owning an espresso machine is keeping it working. To do this, regular maintenance is a must. You can perform simple daily wipe-downs of the case, weekly backflushing (on machines that support it) and regular descalings once or twice a year. All of this will be outlined in your user manual, so be sure to read it! Keep in mind that espresso machines are complicated mechanical devices with moving parts often operating under pressure. It’s normal for wear and tear to lead to part failures, but this is usually a “get it fixed” situation and not a “buy a new machine” one. We even have a repair center that can help you keep your machine in top condition.
Related: Daily and Monthly Cleaning Tips for Your Home Espresso Machine — the routine that keeps the pump, boiler, and group head doing their jobs.
Need a repair? SCG's Repair Center can help with tune-ups, diagnostics, and warranty service.
Shop What We Recommend
Now that you have a better understanding of how espresso machines work, it’s time to pick one out for yourself! We stock machines we trust, and all of them are options we’ve tested and found value in. If you’re a budding enthusiast, you can check out the semi-automatic machines we recommend, and even sort by attributes like boiler type and price point. If you need a hand we’re here to help - we view your machine as an investment (and you should too), and it’s why we have gear advisors and our repair center to help you pick out a machine and keep it running long term.
Shop: All espresso machines — filter by boiler type, budget, or brand to find your fit.
Frequently Asked Questions
How much pressure does an espresso machine use?
Most espresso machines brew at roughly 9 bars of pressure, about nine times atmospheric pressure. The pump generates that pressure, and it's the defining ingredient that separates espresso from drip, pour over, or press coffee.
Can a stovetop moka pot make real espresso?
Not quite. A stovetop pot builds only a small amount of steam pressure, nowhere near the 9 bars a pump-driven espresso machine produces, so it can't extract the concentrated, crema-topped shot that defines true espresso.
What does a PID do on an espresso machine?
A PID is a control board that algorithmically manages the heating element to hold brew water at a stable temperature, rather than letting it swing the way a simple thermostat does. Most PIDs are also adjustable, so you can pick your brew temperature.
Why does an espresso machine need to be descaled?
Every shot runs water through the pump and boiler, and hard water leaves mineral scale behind that can damage components over thousands of shots. Descaling once or twice a year, backflushing weekly on machines that support it, and using filtered water keeps the system working.
Shop Semi-Automatic Espresso Machines
Now that you know how it works, find the one that fits your counter (and your mornings).
Shop Semi-Automatic Machines Already own one? Visit SCG's Repair Center →