In the world of coffee, it’s “pressure” that differentiates the humble shot of espresso from any other type of coffee. Various machines have different bars of pressure to extract the coffee with very different results.
For a novice, this might sound confusing. After all, as a beginner, all you need to know is how many bars of pressure make a good espresso?
When it comes to home espresso machines, the higher the number of bars of pressure, the better your espresso will taste. A double shot from a 9-bar machine will give you a more robust flavor than one from a 3-bar machine.
But there’s a bit more to it than that.
Keep on reading and discover everything you ever needed to know about the bar pressure in your espresso machine.
What Do Bars Of Pressure Actually Mean?
When we talk about bar pressure, what exactly are we talking about.
Ok, bear with me here; this could get a little confusing.
Barometric or atmosphere pressure measures the pressure or force that the atmosphere exerts. Simply put, it’s the weight of air at sea level.
Bars are a metric unit, 1 bar is approximately equal to atmospheric pressure at sea level.
So when making espresso, you usually want 9-bars of pressure or nine times the weight of the pressure at sea level being forced through the coffee grounds.
Getting your head around this can be understandably difficult, especially when talking about how much pressure is used when making a shot of espresso. So to put some perspective on this, let’s take car tires as an example.
Typically a car requires around 32 PSI (pounds per square inch). You would think that this is a large amount of pressure, right? After all, this is a car tire we are talking about.
This is going to blow your mind (no pun intended).
A good shot of espresso calls for 9-bars of pressure. This is the equivalent of 130 PSI – that’s over four times the pressure used in your average car tire.
How Does Pressure Affect Espresso Quality?
So now onto something I’m sure you’re more interested in – how does the pressure affect the quality of your espresso?
If too much pressure is used when making your espresso, there will be less contact time with the water and the coffee grounds; the water will pass through too quickly and make the espresso weaker.
As pressurized water is forced through the coffee grounds, it extracts flavors, oils, and other soluble components as it passes.
Whereas if you don’t use enough pressure, the opposite will happen, and the water will be in contact with the ground coffee for too long, meaning a stronger, more bitter tasting espresso.
Also, with high pressure, you will find that your tamped coffee will be more susceptible to channeling due to the faster flow.
With espresso, it’s all about finding the right balance with the coffee grind, the pressure, water temperature, and consistency to get the perfect espresso.
Pressure is just one element of a good shot of espresso. But what I have experienced is the flow rate through the coffee puck is far more important than picking out an arbitrary pressure profile.
To achieve a constant flow, you should ideally be looking to decrease your pressure due to the erosion of the puck as the shot progresses.
Many of the best automatic machines already do this, so it’s one less element that you don’t need to control.
So, to summarize. What’s happening when you change your pressure will be the evenness of your espresso extraction and the amount of extraction.
When your extractions become uneven, you will notice a sour combination of under extraction and harsh astringency. If your extraction is just low, you find that you’ll get a lot of sours. A higher extraction you will find is going to be sweeter.
How Many Bars Of Pressure For Espresso?
So how many bars of pressure are needed for a good espresso?
If you’ve been playing around with your automatic espresso machine at home for any amount of time, you should already know that several factors need to be aligned to pull the best shot of espresso.
Things like the grind size of your coffee, the water temperature, tamping force, etc., etc., all need to come together.
But what about the pressure? Each espresso maker is different – is more pressure going to be better?
As I briefly touched on in the last section, more pressure will mean that water is forced through your coffee grounds faster. This isn’t ideal, and there’s a reason that experts suggest a recommended extraction time of around 25 to 30 seconds.
To hit this sweet spot and to take into consideration all of the other elements required to make a good espresso shot, around 9-bars of pressure is going to be damn near perfect.
This pressure will help you align to the recommended 25 to 30 second extraction time if all other brewing elements are on point.
So why do some espresso machines come with 15-bars of pressure? How many bars is a good espresso machine?
Let’s find out.
9-Bar vs. 15-Bar Pressure Espresso Machines
If 9-bars of pressure is the sweet spot, why are there machines that offer 15-bars of pressure?
No, it’s not a clever marketing ploy, “more is better.”
The higher pressure means your espresso machine has more power under the hood. In most cases, the full 15-bars of pressure will never be fully utilized.
Going back to the car analogy. Take a Ferrari as an example. It’s fast, very fast, but you will never put your foot to the floor when you’re driving around the city, but the extra power is there if needed.
The same thing is true with a 15-bar espresso machine, they have the power, but it is not used.
Many espresso machines tend to lose pressure between the group head and the pump, so to compensate for this, they start off with 15-bars of pressure (more than is required), but the actual pump pressure that hits your coffee will be around 9-bars.
So taking this into consideration, if your machine were only producing 9-bars, you would not have the adequate pressure going through your portafilter to ensure a great tasting espresso.
– It’s best to have more pressure that’s not utilized rather than an under pressured machine.
A common feature found in many of the best espresso machines is a valve to ensure that the pressure for brewing is always around 9-bars – the excess pressure gets released from the machine.
How About Crema?
The beautiful golden crema that sits on top of espresso is regarded as a sign of a great shot of espresso. The only way to achieve this is with the right amount of pressure going through your espresso machine – ideally 7 to 9 bars.
But it’s not just the proper pressure that guarantees a crema. It also depends on your coffee beans and the fats and oils they contain.
I’m sure a lot of this has gone straight over your head. I get it. It’s also a complex subject to convey.
So to summarize and to keep things simple, the ideal pressure for your espresso should be around 9-bars.
When you’re shopping for a new espresso machine, don’t get caught up in how much pressure they provide.
Many of the best machines will be able to achieve over 9-bars, and those 15-bar machines will have an automatic release valve to ensure that roughly 9-bar hits your coffee and the excess is disbursed.