Espresso machines make strong shots of coffee, but you might wonder, “How do espresso machines work?”
Many parts are involved to create this rich, flavorful coffee. Once you know each part of the machine, you’ll better understand how they work together to craft your beverage.
How Does an Espresso Machine Work?
In a nutshell, an espresso machine heats water using a heating element or boiler, and pumps it through the finely ground coffee beans in the portafilter at the ideal pressure to extract the coffee flavor in a short time.
So brewing espresso requires at least the following essential parts:
- Water source
- Heating element
- Group head
- Filter basket and a portafilter
The keys to delicious espresso hinge on the water temperature and pressure. That makes the heat source and pump the most crucial parts of an espresso machine. But they wouldn’t be able to work without a water source and group head.
The parts of an espresso machine can vary greatly depending on the type you own.
Fully automatic espresso machines do all the work for you. You just need to push a few buttons, and it will pull an espresso shot or even steam milk for you.
Semi-automatic machines require more manual input. Entry-level machines use more basic parts than expensive or commercial machines. You’ll learn the details about each element in the relevant sections.
Read on to find out what parts your espresso machine has and how they work together to give you the best espresso shot.
The Espresso Machine Brewing Process
First, you need water to make coffee. The water source of an espresso machine can be the water reservoir or direct plumbing.
Machines with water reservoirs are most common for home options because you’re only making a few shots of espresso each day. It’s simple to refill the tank when you need it. For home machines, the tank is usually in the back of the appliance.
Commercial espresso machines make hundreds of shots daily, so connecting them directly to plumbing makes brewing easier. Baristas never need to worry about refilling a reservoir. Higher-end home espresso machines with rotary pumps can also connect to your water supply instead of using a water reservoir.
Direct plumbing also automatically provides some pressure behind the water, which simplifies the brewing process.
Heating Element or Boilers
The electric heating elements heat water to the right temperature. This heat ensures you get the most flavor from the ground coffee. Cold, cool, or lukewarm water isn’t enough to get that richness that makes espresso famous. The espresso machine with a PID can heat water to the exact temperature to extract the right flavor, oils, and caffeine from the coffee grounds.
Water flows from the reservoir or plumbing into the heating element or boiler. The pipe is a one-way passage, so cool water flows in, heats up, and exits through another outlet to reach the group head.
Size can impact a boiler’s efficiency. Big boilers heat enough water for several espresso shots, but they use more energy. When buying a home espresso machine, you’ll want to consider how many shots you’ll make at a time.
You can quickly make several shots with a larger boiler, but you’re using extra energy. However, with a smaller boiler, you must leave it on longer. You must also wait to pull each shot once the water gets hot enough.
One type of heating element in an espresso machine is the thermoblock. It’s made of stainless steel and aluminum. Water flows through the spiral pipe and picks up heat from the thermoblock, then exits at the right temperature and flows to the group head.
Many entry-level machines use thermoblocks as the heating element. They’re efficient and heat up quickly. For example, Breville’s Barista Pro takes only 3 seconds to heat up, while most espresso machines with a boiler need extra 15 to 30 mins to warm up.
The aluminum and stainless steel metals don’t easily grow scale deposits. If you have a machine with scale build-up, it can negatively impact the taste of your espresso.
Many espresso machines for home use also use a small boiler to heat water instead of thermoblocks.
A semi-automatic espresso machine with one boiler can’t brew an espresso shot and steam milk simultaneously. You need to give the boiler time to heat up for the espresso shot and pull it, then let the boiler heat up to a higher temperature for steaming milk. If you want to pull another shot, you’ll let it cool down to brewing temperature before using it.
Dual boiler machines are a step above single boiler machines. With two separate boilers, you can brew espresso and steam milk simultaneously. This ensures you brew a hot milk-based espresso drink instead of waiting for the machine to cool or reheat.
Another benefit to dual boilers is how you can control the temperatures. You can increase or decrease the heat to suit your specific tastes. This ability ensures you can make espresso to your liking. Each tank can heat the contents to the correct temperature, providing better temperature stability and steam pressure.
A heat exchanger is often used in high-end machines. It holds water in the heating chamber and boils it to the steaming temperature. There’s a tube inside that chamber, which circulates water between the group head and the tube to keep the optimal brewing temperate. In that case, heat exchanger machines also allow you to steam milk while making espresso. The ability to do both at once ensures you can enjoy your beverage while it’s hot.
However, if you let your espresso machine sit idle for too long, the temperature of the brew water will rise. So you’ll need to run a cooling flush to cool down the brew water a bit.
We explained the espresso machine boiler types in another guide, you’ll know more about their pros and cons.
The pump is a crucial part of your espresso machine because it creates pressure so that the water is forceful enough to push through the compact coffee puck. Espresso machines use anywhere from 9 to 15 bars of pressure in this process. Pressure is crucial to get the right flavor from the grounds.
Nine bars of pressure is the equivalent of 130 PSI. Your car tires only need about 35 PSI, so that gives you an idea of the strength of espresso machines.
The pump first pulls the water from the reservoir to send it to the heating elements. Once the water boils, the pump continues its work by pushing the water through the coffee grounds.
While the first espresso coffee machine used a lever to push the water through the filter, that feature is now automated. That’s why making espresso is also called ‘pulling a shot’ of espresso. Many manual espresso machines still use levers to create the necessary pressure.
Now, most modern espresso machines use electric pumps – vibratory or rotary pumps.
Many entry-level or mid-range machines often use vibratory pumps.
The internal magnet includes a piston and metal coil. The electricity flows through the coil to move the magnet. As the magnet moves, it allows the water to flow through your espresso machine.
These pumps are the most common type found in espresso machines because they’re so efficient. The magnet pushes 60 times per second, so the water has strong pressure as it flows through the machine. If your home espresso machine isn’t working properly, it might be a faulty vibratory pump. Thankfully, these parts are easy to replace and don’t cost much. However, they are generally louder.
You’ll find rotary pumps in more expensive machines.
A rotary pump contains a small motor that spins a sectioned disc. The disc presses on the sides of the pump to instigate pressure. Water flows through this section and gets forcefully pushed out as the disc spins. They are much larger than vibration pumps but quieter and more durable.
All the espresso machine parts above are important, but the group head is where the shot forms. The group head is where the boiling water hits the coffee puck.
Saturated Group Heads
Saturated group heads function as extensions of the heating element. It reaches the same temperature as the boiler because the hot water saturates it. Since these parts weld onto the boiler, it’s hard to replace them.
Semi-Saturated Group Heads
Semi-saturated group heads are parts separate from the heating element. A water intake pipe funnels into the boiler to pull the water into the coffee filter. These parts are easy to repair or replace.
E61 Group head
The E61 group head got its name from an old espresso machine called the Faema E61. These parts are heavy, expensive, and require a longer preheat time. It is often used for prosumer-level machines. Many Baristas agree that the E61 delivers better temperature stability.
Filter Baskets and Portafilter
The portafilter, or portable filter, is a filter basket holder with a handle so you can easily pack your coffee grounds. Tamp them firmly and then lock the portafilter into the machine so the pressurized water can push through.
Pressurized portafilters have a single hole at the bottom for the espresso to exit. A non-pressurized portafilter has a grid of holes for the espresso to filter out as it brews. The shot quality from the latter is superior but requires a more accurate grind size. We compared the pressurized vs non pressurized portafilter in detail in another post.
It’s important to prepare your coffee puck for the best possible shot of espresso. If you use loose-packed grounds, the water can easily flow through them. As a result, you’ll get weaker coffee, both in terms of taste and caffeine content. If the puck is not well distributed before tamping, you will get channeling that affects the taste of your shot.
The steam wand is optional—you only need it if you’re making milk-based espresso drinks. You need smooth and creamy milk foam to create a drink like a cappuccino or a latte.
As previously mentioned, steam wands use different temperatures compared to what’s needed to brew espresso. Therefore, it’s ideal to have a dual boiler or a heat exchanger that can make espresso and steam milk at the same time.
Knowing how your espresso machine works to create a shot gives you a new appreciation for the machine.
The next time you pull an espresso shot, carefully watch the entire process. With the knowledge from this article, you should be able to see what your machine is doing every step of the way.