Professional espresso machines are increasingly seen in offices and homes. It’s great that we can get our specialty coffee fix at work or without leaving the house, but how much do you really understand about what happens when you dial in a shot?
The sleek casing can hide significantly different mechanisms. Let’s take a look under the cover and learn more about espresso machines.
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An espresso machine surrounded by steam.
It is reported that in 1884, Angelo Moriondo presented “new steam machinery for the economic and instantaneous confection of coffee beverage” at the Turin General Exposition. The pressurised coffee system was born.
Electric steam-driven machines are still in use today. Their simplicity makes them easy to use and maintain, and they are affordable and compact. But how do they work?
Within an airtight tank, water is brought to boiling point and steam is created. This produces pressure, which forces the water through a reservoir and into the coffee. It’s similar to what happens inside a stove-top moka pot.
The downside of steam-driven machines is that they only reach 1–1.5 bars of pressure. The ideal pressure for a shot of espresso is 9 bars.
Learn more in How Does Pressure Affect Espresso Quality?
A barista prepares an espresso-based drink.
In these machines, the water used to create steam is also used to brew the coffee. This means the water is near boiling when it reaches the beans and can make the coffee taste bad due to over-extraction.
Iván Mora is a barista at Hola Coffe in Madrid. He says that in steam-driven machines “not only is pressure low, but temperatures are very high”.
Steam-driven machines work well if you want a quick espresso without too much investment of time or money. With some experimentation with grind size you may be able to figure out how to produce a well-brewed cup without over-extraction.
The Mirage Idro is a lever group machine from Dutch manufacturer Kees van der Westen. Credit: Gisselle Guerra
Lever-driven machines require physical strength to pull a shot. There are two kinds: manual and spring-loaded.
A manual machine can be recognised by the horizontal resting position of the lever. When it is raised, an opening in the brewing chamber draws in pre-heated water to saturate the grounds. The barista can control the length of pre-infusion, flow rate, and pressure by when they bring down the lever.
In spring-driven machines, the lever points up when the internal spring is relaxed. Pulling the lever down causes the spring to compress and brings the piston up. This creates space in the brewing chamber for water to enter.
The lever comes back up as the spring releases its tension. This causes the piston to push the water down and extract the espresso.
The moment of extraction. Credit: Neil Soque
With lever machines, the barista is in control. If a certain coffee needs a longer pre-infusion or extracts more flavour with a distinct pressure profile, it is easy to do this. They allow creativity and experimentation.
Lever machines are eye-catching and the lack of electrical components can be appealing. They aren’t often used today and certainly aren’t ideal for a busy coffee shop, but if you want a steampunk method of making coffee, this kind of machine is for you.
But why should pulling an espresso be hard work? Lever machines take physical effort and an understanding of how to control variables. And total human control can create inconsistency.
Most lever machines have only a single boiler and rely on the water cooling down before it reaches the coffee, which can be inconsistent.
Shaun Aupiais is the founder of Red Band Barista Academy in the Eastern Cape, South Africa. He tells me that he values consistency. “There are so many pros and cons when it comes to purchasing equipment, but consistency, for me, is definitely is one of the most important things,” he says.
An Ethiopian single origin. Credit: Max Haydon
Pump-driven espresso machines have been around since the 1960s and dominate the market. They work by using an electronic pump to drive pre-heated water through the brew chamber and into a bed of coffee. With an electronic pump, it is easy to achieve consistent high pressure.
Today, there are three main categories of pump-driven machine: semi-automatic, automatic, and super-automatic. Within each there are variations including types of pump, number of boilers, and computer-aided programming. But let’s clarify the different types before looking at the mechanisms.
An espresso machine with touch-screen control panel.
This is probably what you imagine when you think of a professional espresso machine. Semi-automatic machines use an automated system to drive the water through the grouphead. Grinding, tamping, and control of extraction time are the responsibility of the barista.
They are a good compromise between human control and mechanised consistency. You’re in charge of the shot, but there is regulated water pressure and temperature so it’s harder to mess up.
These are very similar to semi-automatic machines, but they automatically stop the flow of water. This ensures consistent volume in each shot and means you don’t have to stand over each espresso to stop overflow. Automatic espresso machines are also used in cafés.
Super-automatics do it all. The machine grinds the beans and measures, fills, and tamps the grounds into the portafilter. Press a button and get a consistent shot every time. Some machines let you make adjustments to grind size and timing, but there is little room for creativity. They tend to be used in homes and offices, rather than coffee shops.
Learn more in What You Need to Know Before Buying an Espresso Machine
Shots of espresso on a bar. Credit: Neil Soque
The Mechanics of a Pump-Driven Machine
There are different kinds of pumps in these machines: vibrating, rotating, and geared. Ivan tells me that vibrating pumps are usually used in super-automatic machines and that they are “really unstable when it comes to controlling pressure, since they work with a fixed pressure”.
He says that “the pressure can go from 4 bars at the beginning of the extraction up to 14-16 bars when they finishing the espresso”. There are situations where you may want to vary the pressure profile, but, as we know, unplanned uneven pressure can create a bad espresso.
Pulling an espresso.
Professional-grade machines usually use either rotating or geared pumps. Ivan tells me that “rotating pumps are constant and stable. However, you have to adjust them based on their deterioration and as time passes.”
“Geared pumps are found in the best machines and they work together with rotating pumps but with independent control of pressure,” Ivan explains. “The pressure can be varied with manual changes or with programmable options that the barista sets depending on the extraction profile they desire. Some espresso machines incorporate both manual and programmable options.”
Professional pump machines often have three-way release valves to release pressure and allow multiple shots to be pulled in quick succession.
An espresso in the cup.
The advantage of a semi-automatic or automatic pump-driven machine is control with consistency. This is why high-end pump machines usually have multiple boilers. They allow the brewing water to be heated separately from that used to create steam. This allows better temperature control and reduces the chance of over-extraction.
Shaun tells me that “with more advanced temperature control you have individual boiler units where you’ve got an individual boiler for a grouphead as well as [ones for] your water and steam.”
But Ivan cautions that even with a high-quality machine, there will be some inconsistency. “There are some machines that are better than others, but don’t forget that these machines are created by us humans and we are not perfect, so there is no perfect espresso machine,” he says.
A barista station with red La Marzocco espresso machine. Credit: Gisselle Guerra
The Price of A Consistent Espresso
Semi-automatic and automatic pump-driven machines may provide a good balance of consistency and control over other options, but they can be expensive.
Shaun says that machines with multiple boilers “obviously come with a price point. It’s such a catchy situation from a barista’s perspective… budget plays a massive role in all of this.”
Pump-driven machines can vary widely in price, but by understanding the basic mechanisms you can make an informed choice. Are you paying for increased control and stability or just good looks?
Pulling an espresso. Credit: Neil Soque
There are pros and cons to each type of espresso machine. With differences in consistency, affordability, and practical considerations, the “best” machine is different for each person.
Developments in espresso machine technology are taking place all the time. New components, pneumatic systems, and computerised controls are being developed by manufacturers around the world.
It is easy to be seduced by a good-looking machine or high-tech features, but underneath the stylish shells there are some major differences. Before committing to a purchase, ask whether the machine really fits your needs.
Enjoyed this? Check out How to Clean & Maintain Your Espresso Machine
Written by Max Haydon.
Perfect Daily Grind
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