How Many Bars Of Pressure Is Good For Espresso?

Pressure is the one thing that sets espresso apart from any other type of coffee. While you might be able to get a short, concentrated brew out of a range of coffee makers, it’s the high pressure that will create the signature richness and crema that we love.

When it comes to just how much pressure is needed, you might see a few different figures being suggested. So just how many bars of pressure make a good espresso?

What do we mean by bars of pressure?

First of all, let’s get clear on exactly what we’re talking about here. If you’ve ever put air in your tires, you’ll be familiar with measuring pressure in PSI. A bar is simply a different unit of measurement, the way that kilos and pounds are two ways of measuring mass. The bar is not one of the International System of Units, but it’s commonly used in things like scuba tanks and of course espresso machines (1).

Bars are a metric unit, with 1 bar being approximately equal to atmospheric pressure at sea level. So when we talk about an espresso maker using 9 bars, the water is forced through the coffee grounds at a pressure nine times that of the natural atmosphere.

Pressure is used in a few different brewing methods, including the Moka pot and AeroPress. However, the pressure in an espresso machine is much higher. The original espresso machines used steam pressure, but with the advent of electricity, this was largely replaced by vibratory or rotary pumps in automatic or semi-automatic machines (2). 

How many bars of pressure for espresso?

As you will be aware, there are several factors that go into creating the perfect shot of espresso: brew ratio, brew time, and brew temperature. The other variables that you might think of, such as grind size, water pressure, and tamping pressure, will all have an impact on one of these three.

The higher the pressure, the faster the coffee is extracted from the grounds. So in theory, you could get a quicker cup of coffee if you just amped up the pressure. But there’s a reason that the suggested extraction time for espresso is between 25-30 seconds.

It’s the balance of all these elements that counts. But taking into consideration all the other things that create a good espresso, nine bars has been found to be the sweet spot. 

9 bar vs 15 bar espresso machines

So if 9 bars is the ideal pressure for pulling a shot of espresso, where do 15 bar coffee makers fit in? You have probably seen many home machines advertised as producing 15 or even 18 bars of pressure, with the idea that more is better. The truth is that with cheaper espresso machines, they tend to lose a lot of pressure between the pump and the group head. So while they might start off at 15 bars, you will still be brewing at around 9 bars (3). And in fact, a common feature of many high quality espresso machines is a valve to prevent the machine from brewing at more than 9 bars (4). 

Final thoughts

In a nutshell, brewing pressure should be around 9 bars for creating a great espresso. But when shopping for a new machine, don’t worry too much about the bars that are advertised. If you do want to get into the technical side of brewing, look for a machine with adjustable pressure and pressure gauge.