Pressure is what separates an espresso from other brewing methods. It’s this pressure that allows us to brew a concentrated shot of coffee in 25 seconds. It also gives us the syrupy texture and foamy crema that we love. But the exact amount of brewing pressure needed can be confusing.
So, how many bars of pressure for espresso? Well, as a minimum you need 9 bars of pressure for brewing espresso. While an espresso machine may boast 15, 18, or even 20 bars of pressure, much of this is lost between the pump and the brew head. The “Italian Espresso” refers to the coffee from a Bialetti Moka pot which only brews with 1 bar of pressure.
There’s quite a lot to this, including what on Earth a “bar” is in the first place. So read on, as we explain everything pressure related and how it can help you pull a good espresso shot:
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1 bar is the atmospheric air pressure at sea level. In simpler terms, it’s the weight of the air pressing down on you. If you go 10m (33 feet) underwater, you’ll be at 2 bar.
If you want to experience the same 9 bar pressure as the coffee grounds in your espresso machine, you’d need to go 80m (260 feet) underwater.
It may be easier to understand if we convert to PSI. If you drive, you might have come across PSI (pounds-force per square inch) in your tire pressures. Maybe 30-35 PSI is the correct pressure on your car. Well, espresso is extracted at 130 PSI.
Pulling espresso is a balancing act between the weight of coffee grounds, grind size, water temperature, brew ratio, pressure level, and brew time. So, there’s a lot going on inside your home espresso machines.
Getting a perfect 1oz espresso shot requires all of these things to be in harmony. When it is, you extract all the flavors you want from your favorite espresso coffee beans and none of the undesirable flavors.
Using a super-automatic espresso machine takes care of this calculation for you. But, if you prefer manual espresso machines, all of these factors have to be controlled by you each time. So it will take more time, practice, and skill to pull a great-tasting espresso.
While the espresso Gods don’t all agree on one exact recipe, the general consensus is that a coffee-to-water ratio of 1:2, brewed at 200°F with 9 bar pressure for 20 to 25 seconds will pull the perfect espresso.
So all of these elements can be altered to your preference. But that is the baseline for pulling great espresso shots.
Both the Moka pot and AeroPress use pressure to quickly brew coffee with a more intense flavor than non-pressurized methods. These both only reach around 1.5 bar of pressure though, nowhere near what an espresso machine produces. Although this is pretty on par with the original espresso machines of the early 1900s.
Moka pot coffee is often referred to as “Italian espresso” rather than “true espresso.” It was invented in the 1930s in Italy to bring quick, simple “espresso” to the masses. At the time, the 1-2 bar pressure was the best around, and even today with the invention of modern espresso machines, it remains widely popular the world over.
The Bialetti Moka pot brews an incredible cup of joe in its own right but, compared to an espresso shot, it doesn’t have the same strength, depth, or body. However, when comparing the Moka pot to the French press‘ immersion brewing or to a drip coffee maker, the resultant brew is much richer and more syrupy.
Then there’s the AeroPress: a simple style of coffee maker that has taken the coffee world by storm.
It uses manual pressure from the user to generate extra force for brewing coffee. And no matter what you bench, it’s just not feasible for a human to generate 9 bars of force. However, with a little flexing, it’s possible to generate around 0.5 bar pressure with the AeroPress coffee maker. Whilst this is only a little over atmospheric air pressure, it does create a richer brew which some use like espresso. But it’s still well short of the threshold for “true espresso.”
Well, pressure is a little more complex than it first appears. To pull espresso, the water pressure is generated at the pump which then enters the group head where the hot water enters the filter basket (inside the portafilter). But that initial pressure from the pump isn’t always maintained throughout this journey.
Most espresso machines generate 15 bar pressure with either a vibratory or rotary pump. This differs from the original espresso machines which used steam pressure. But, no matter what pressure-generating method is used, by the time the water reaches your ground coffee this has dropped to the desired 9 bars needed for espresso.
In fact, some of the more expensive high-end espresso machines will even have a pressure valve. This ensures that you don’t brew with too much pressure (more than 9 bars) as this would ruin your delicious espresso shot.
The 3.5 bar cheaper espresso machines can make an intense shot that works well enough for casual users. But it won’t have the depth or complexity of the higher-pressure machines.
First up, you need to assess the build quality of the espresso brand rather than the pressure from the pump. For example, a high-quality Breville espresso machine with a 15 bar pump is more likely to deliver the consistent 9 bar pressure than a low-quality, under-pressured machine with an 18 bar pump.
Then there’s the pump itself: is it a rotary pump or a vibratory one?
Rotary pumps are always better than vibratory ones, both in terms of noise and delivering the optimum brewing pressure. There are still many espresso machines out there that are steam pressured. These tend to only be from cheaper espresso machine manufacturers as it’s a less stable pressure generation method and can result in burnt coffee.
If you’re in the market for a manual espresso maker, we’d recommend choosing one with a gauge (like the Flair Signature). This allows you to measure the espresso pressure at the filter basket, keeping you on the right track for consistently generating enough pressure.
So, always look beyond the raw numbers when judging espresso machines. Consistent delivery of 9 bar is what you need, not enough pressure to crush coal into diamonds.
Even if you live at 12,000 feet above sea level, a full 3,000 feet higher than the highest city in the US, the pressure only drops from 1 bar to 0.65 bar. Something your machine can easily compensate for.
So, unless you’re consistently brewing espresso high up in mountain ranges, it’s not really worth worrying about the change in air pressure on your espresso brewing. The more pressing concern would be your water temperature as the boiling point of water varies much more wildly at altitude.
9 bars is the optimum pressure for espresso brewing. But anywhere between 7 and 9 bars will produce the rich, syrupy shot you love.
The key is consistent delivery of this pressure to ensure perfect extraction. Whilst the actual pump pressure advertised may be much higher than this, the aim is to ensure the pressure at the point of extraction is consistently correct.
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