How Espresso Machines Work - A Coffee Lovers Guide

How Espresso Machines Work – A Coffee Lovers Guide

Ever wanted to know how espresso machines work? This article is for you as I explain as best as I can in a simplified non-detailed manner following the water from its input to the final output, a great shot of espresso.

Not all espresso machines are the same internally but most work around the same general process with only slight variations on the type of pump, how pressure is maintained. Water goes in, coffee comes out, let’s move on and talk about that middle part and how espresso machines work.

Let’s start with…

Understanding The Lingo – The Key Terms To Understand

Let’s have a quick drill down on the lingo involved with espresso machines to make sure we are on the same wave length.

Dialling in o pulling a shot: This is coffee talk of meddling around, making small adjustments to your machine to tweak and control settings associated with the brewing process to have your machine brewing the perfect shot. This also refers to the grind size, amount of grounds used, tamp, extraction time and water temperature.

Tamp: Tamping is an easy skill to master, very easy, but you need to get it right or you will get channelling and a low quality crema. It is simply the compression of your coffee grounds in an even manner.

Grouphead: This is the part of your espresso machine where you attach your portafilter. It is where the hot water comes out and over your coffee grounds.

Portafilter: Your portafilter is the detachable part with a handle and where you put the finely ground coffee grounds. As the name indicates, it is a filter.  If, better said, when the ideal pressure as well as the ideal temperature are achived together you will get a perfect decadent espresso.

Bars of Pressure: This is an international unit of measurement that measures the barometric pressure of the water your espresso is made at. 9 bars of pressure (130 PSI) is what is required to get good thick crema on your espresso. This is one setting you may need to “dial in” initially. It is fairly possible that you may need more than 9 bar (130 PSI) of pressure, most certainly no more than 15.

Now we have that out of the way let’s crack on with the water and the pump.

Understanding The Lingo - The Key Terms To Understand
There are key terms to understand

Read: Pump driven espresso machine

The Water Source And The Pump

Any cup of coffee made with any machine be it an espresso or any other coffee drink starts with a water source. Without water, obviously you have no coffee. Water is either filled via a plumbed connection as is the case with a professional machine, or is drawn from a reservoir that is filled manually by the home barista.

A high quality espresso needs high quality water. The best water is distilled water, next best is bottled water and after that filtered water.

I strongly advise filtering your water as this also serves as preventative maintenance and will help to prolong the life of your machine.

Water on its own is not going to get the job done. It requires a pump to provide the required pressure to force it through the coffee puck to produce a great shot of espresso.

The most common type is an electric pump which is used to produce the pressurized water needed to produce a high quality crema.

The electronic pumps come in two types, rotary motor and a vibratory motor.

The rotary motor spins and uses “paddles” inside it to move water and maintain pressure. A vibratory motor has a magnet that is inside of a coil that moves back and forward to allow the water to move and maintain consistent pressure.

A manual espresso machine uses a spring to achieve the predictable pressure and is operated manually.

The Water Source And The Pump
A twin spout portafilter

Read: Kona Coffee Vs Arabica – Is Kona Coffee Arabica Or Robusta?

The Different Types Of Boilers

This part can be a little more complex, and since it is the most VIP part of an espresso machine, especially modern espresso machines. As it is with an espresso shop and any espresso drink that you are making, you absolutely need your water to be at the Ideal and optimal temperature.

Note: The correct temperature is 195F to 205F (92C to 96C).

Water is brought into your boiler via the one-way valve where the water is stored and heated.

Semi-automatic espresso machines have one of three different types of boilers, a heat exchange, single boiler and a double boiler.

A Single Boiler

This is exactly what the name suggests that it is, a single boiler where the same boiler is used for steaming your milk that is used to heat the water that makes your espresso.

The main draw back of this kind of boiler is that you cannot use both at the same time, to say you can’t both brew you coffee and steam your milk The result of which is taking you longer for you brew a latte and other milk based drinks.

Single boilers are only used in low end cheap machines.

A Single Boiler
The grouphead of an espresso machine

A Dual Boiler

A dual boiler, also appropriately named, is an espresso machine with two boilers. One boiler heats the water that you use for making your coffee and the other boiler heats the water that is used to steam your milk.

The advantage is obviously the ability to both make your espresso and to heat your milk at the same time. It is the best option for the stability of water temperature.

If you are likely to make a lot of milk based drinks like lattes, Mochas, Macchiatos, cortado, flat white and so on. The temperature stability also permits you to make more cups of coffee at the same time.

These are the most common type that you will find in commercial machines and automatic espresso machine and semi-automatic espresso machines.

A Heat Exchange Boiler

This type of boiler is a single large boiler that has a section inside the boiler that is isolated and seperated from the principle heating element.

The isolated section of the heat exchanger is what provides water that is more suitable for brewing your coffee. The other chamber, is hotter, which is the water that is used for steaming your milk. The result of this design is the ability to heat the water at two different temperatures which ensures you are never short of water for brewing your coffee or for steaming milk with your steam wand.

You can and will make better quality espresso shots with a heat exchanger than you would with a single boiler.

The Group Head

Also spelled as one word, grouphead, which I touched on earlier. It is the part where the hot water comes out on the front of your home espresso machine. This where you attach and lock your portafilter on to.

When you are making a shot of espresso the valve opens and pressurized water flows from the grouphead and through your coffee puck.

Depending on the size of your expresso machine you will have one or two group heads with the much bigger, more professional ones having 4. With the right combination you will be able to brew up to  shots of espresso at a time.

A home machine usually has only one grouphead.

Bottomless grouphead
A bottomless grouphead

The Portafilter

The portafilter we have already touched on. This is where you put your coffee grounds, and it comes with a small metal filter basket, often referred to as the portafilter basket that clips inside. There are two types of design, single outlet for a single espresso and a dual outlet for brewing two shots of espresso.

A common question asked is which is better – spouted or bottomless portafilter.

A spouted portafilter has a single or double spout from which your espresso shot flows out of. A bottomless portafilter is exactly as it sounds, bottomless. Your coffee flows directly over your coffee grounds and into your coffee cup.

Baristas and perfectionists love the bottomless as they allow you to see any problem and have the ability to see what problems may be arising such as channelling and permit you to get a more perfect shot.

It is not a big deal what type of portafilter you use. If you are a perfectionist, you can go for a naked bottomless portafilter that allows you to observe the flow of water/coffee clearly.

The Steam Wand

Surprisingly, not all espresso machines have a steam wand. It is certainly advantageous that you have one. This goes even more so should you plan on making milk based espresso drinks.

`In fact, it is obliged as they make much better frothy milk than others. Plus, a steam wand is much better and easier to keep clean.

Ensure your machine is a double boiler if you are looking for one with a steam wand.

Steam wand
A steam wand

The Control Panel

The part that many forget to talk about. The control panel is exactly as it sounds, it is the panel with the on/off switch, indicator lights and can have various options to press relating to the coffee that you are brewing and/or a straight start/stop switch.

Pressing a button here will open a valve which controls the flow of water to the grouphead via a micro switch.

What Happens When You Pull A Shot?

Let’s see how this all comes together when you pull a shot of espresso. Let’s start by happily assuming you already have your machine filled with water.

Switch your machine on and wait for your heating light to tell you that your water is at the proper temperature for brewing your shot. Use your temperature probe to measure and record the temperature, you may need to adjust this later to dial in your espresso.

You can skip the exact temperature control if your coffee machine has a digital temperature control.

Your next step is to grind your coffee to a very fine grind size, the finest that your coffee grinder permits is perfect. 80 microns (1/32 inch).

Now focus on your tamp and tamp your ground coffee evenly and with not too much and not too little pressure.

Now place your portafilter by attaching it into your espresso machine.

Place a Demitasse cup below it and press the appropriate switch on the control panel to pull your shot.

The micro switch will start the pump which in turn pressurises the water and heating chamber to 9 bars of pressure (130 PSI). This will force hot water through your coffee puck and out of the spout and into your cup.

The whole process should take about 25 to 30 seconds.

If you are making an espresso, steam your milk by submerging the nozzle of your steam wand and moving your milk jug up and down to heat the milk and forth it at the same time.

There are literally dozens of coffee drinks that you can make with your espresso machine.

A Great Coffee
The result is a great coffee

 Keeping Your Espresso In Prime Condition

Regular bi-annual maintenance will keep your home espresso machine in tip top condition for every shot that you produce.

Using a water filter is an excellent preventative maintenance step you can take to prevent the build up of lime and mineral deposits. No matter how good or how expensive your machine is, you need to maintain it at least 2x per year.

Keep your eye on the reduction in the quality of your coffee deteriorating, tasking a little off. If your grouphead is leaking, you may need to replace the gasket. This is a very easy job that can be done by yourself or by a maintenance specialist. There is nothing to it really!

Also, keep your eye open for a leaky steam wand. You might get away with descaling to solve this issue, but in the long term, the gasket for your steam wand will need replacing.

If your hot water tap is leaking, this is a sure sign of limescale, and you will need to descale your espresso machine.

Give it a good proper descaling at least once every 3 months to stop it from building up even if you have no signs of limescale building up.

Maintain your espresso machine well, and it will last you for at least 10 years.

How Do Espresso Machines Create Pressure?

Most modern machines, literally all of the use an electric pump to create pressure to make a perfect espresso shot. Either a vibratory or rotary pump is used.

Old fashioned manual pump machines use a lever that needs to be pumped to create the pressure. Newer pump based machines use a spring based pump to create the pressure required.

Older, now almost defunct espresso machines use steam to create the pressure.

What Is Special About Espresso Machines?

They produce almost boiling water at a pressure to create an excellent coffee that you could not otherwise produce without one. No other coffee brewing machine produces the pressure required to get the rich crema on top.

An espresso machine needs not to be expensive or automatic as manual lever machines can produce an exceptional espresso.

Why Is My Espresso Machine Not Building Pressure?

The problem may not necessarily be related to a component of your machine. First check your grind size, if it is too coarse and not a powder like grind then it may well have something to do with that. Also poor tamping will cause a lack of pressure build up.

Check these two first before investigating further.

Final Thoughts Frappé-Ing It All Up, How Espresso Machines Work

Now you know about the internal architecture and the important parts of an espresso machine and a basic level how espresso machines work. Knowing this will help you to better understand your machine and perhaps which one is more suitable and meets your needs best.

Coffee is love, it's more than love — it's a passion of mine. I've had the luck to have travelled and enjoyed the most exotic of coffee's and unique flavors, brewing methods and techniques of making the perfect coffee from Thai hill tribe coffee to Indonesian volcanic coffee, Malaysian coffee that comes in a tea bag and the array of flavors in Vietnam, from Vanilla to Orange to Coconut to Avocado to even salt coffee and the famous egg coffee. The best part of my coffee adventures is getting to mix with the locals over a nice brew and learning how they make it! I'm cited and referenced on Google Scholar for the topic of coffee.

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