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9 Bar vs 15 Bar Espresso
Comparative analysis between 9 Bar, 15 Bar, and 20 Bar Espresso Machines, and answers to common questions.
Published December 23, 2021
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Jennie Backteman
The Coffee Lab
@ Hammarö, Sweden
Jennie Backteman
Coffee experts@The Coffee Lab
Any coffee lovers out there looking to buy an espresso machine might already have come across terms such as 9 bar or 15 bar espresso machines, but most don’t really know what that means. Naturally, they are left with plenty of unanswered questions such as what exactly is a bar? What are 9 bar, 15 bar, or even 20 bar espresso machines? Does a higher “bar” number indicate quality or performance in some way? The list of questions is pretty long, so that’s where we will begin here, before moving on to a detailed comparison of 9 bar vs 15 Bar vs 20 Bar espresso machines.
What Does the Bar Number Indicate?
The Bar is a metric unit of measuring and representing pressure that’s equal to 100,000 Pa (pascal) and 100 kPa (kilopascal). 1 bar of pressure is also barometrically defined to be almost equal to the earth’s present atmospheric pressure, as would be found at an elevation of 111 meters (59°F). Whenever you hear or read about a 9, 20, or 15 bar machines, that’s exactly what the bar number on it indicates.
For the sake of simplicity and understanding, the pressure capacity of espresso machines can also be converted into pounds/square inch, aka psi. Note that since 1 bar is equal to 14.5 psi, when we are pitting 9 bar vs 15 bar vs 20 bar espresso machines against each other, we are essentially comparing coffee machines capable of producing:
- 14.5 psi x 9 bars = 130.5 psi of pressure (9 bar espresso machine)
- 14.5 psi x 15 bars = 217.5 psi of pressure (15 bar espresso machine)
- 14.5 psi x 20 bars = 290 psi of pressure (20 bar espresso machine).
How and Why Are The Bar Numbers Relevant?
To answer this question, we need to understand exactly how coffee machines use their capacity of producing the bars of pressure first. A coffee machine’s bar number denotes the maximum atmospheric pressure multiplier that the machine can generate as it forces hot water (194°F - 203°F) through the coffee beans. Therefore:
- A 9 bar espresso machine can at best force heated water through coffee at 9x the present atmospheric pressure of the earth.
- A 15 bar espresso machine can at most, force heated water through coffee at 15x the present atmospheric pressure of the earth.
- A 20 bar espresso machine should technically be capable of forcing heated water through coffee at and up to 20x the present atmospheric pressure of the earth.
As previously mentioned, 1 bar indicates the approximated atmospheric pressure of earth at an elevation of 111 meters and a temperature of 59° Fahrenheit.
The pressure capacity of a coffee brewer is important because it can play a big role in determining how strong, bitter, or mild your brew will turn out to be. We should note that the strength of any brew is not only determined by the espresso machine’s pressurizing capabilities, but it is certainly one of the major influencing factors. From the water temperature to the bean’s origins, it all matters in varying degrees. Next, we will go into details regarding how the water pressure affects your brew.
Is there a Perfect Bar Count for Making Espresso?
As it turns out, there is indeed a perfect pressure or bar count that is attributed to making the perfect pot of espresso coffee and it’s not exactly the 15 bar espresso machine. The ideal water pressure for making espresso has always been 9 bars, but those 9 bars of pressure must be maintained at the brew head and not just generated at the pump. Therein lies the issue as domestic coffee makers seldom have the capacity to generate and maintain 9 bars of atmospheric pressure throughout and until the hot water reaches its brew head.
While this technically means we should only need a 9 bar espresso machine for brewing the textbook pot of espresso, there is a high chance that will not happen with a domestic 9 bar espresso machine. The pressure will go down in transit, leading to a weak brew. Repeating the process might improve your brew’s strength, but it will almost certainly leave your coffee tasting more bitter than it should. There are some exceptional domestic products out there that can both generate and maintain 8 - 9 bars of pressure from pump to brew head, they can be very expensive.
Is a 15 Bar Espresso Machine the Ideal Choice for Home?
If we were to compare two average coffee brewers where neither is particularly premium, then the answer is yes. It has been found that even a decent, 15 bar espresso maker should be able to deliver pressurized hot water at its brew head with the ideal 9 bar count. The water will continue to lose pressure as it rises from pump to brew head, but 6 bars of pressure is enough buffer to ensure that the water pressure will never be lower than 9 bars.
What we need to note is that this isn’t universal and there are plenty of useless 15 bar espresso machines out there that cannot maintain 9 bars of pressure, and they would be outclassed by premium grade 9 bar machines. Then, of course, there is the big question about what happens when a 15 bar espresso machine delivers pressurized water at the brew head that is carrying more than 9 bars of atmospheric pressure?
Well, the answer is highly variable as it depends on exactly how much pressure the water did end up carrying with it at the brew head. For example, if the water reached the brew head at 12 bars of pressure, you would have a very strong and bitter concoction in the pot! At the same time, 10 bars of pressure for a pot of espresso is nothing to worry about. It might make your morning espresso slightly stronger, but the coffee should not taste bitter.
As you can probably guess by now, consistency is another highly valued attribute that people look for in their 15 bar espresso machines. Whether the final pressure is 8 bars or 10 bars, the machine must be capable of maintaining that same final pressure at the brew head, each and every time someone brews a pot with it.
15 Bar vs 20 Bar Espresso Makers: Is there a Winner?
We have already cleared up everything that one needs to know about bars, pressure, consistency, etc. while coffee brewing with a machine. We now know for a fact that 15 bar coffee machines are capable of delivering better value for money than the average 9 bar espresso maker, as long as the pressure remains consistent at the brew head.
Nevertheless, this brings us to the mythical 20 bar espresso machines and their bewildering presence in the domestic market. If 15 bars of pressure is considered to be sufficient for ensuring that water pressure never goes below 9 bars from pump to head, why would one even need the extra 5 bars that a 20 bar espresso machine is technically capable of generating?
There are two possibilities here, which means that either:
- The machine simply cannot deliver hot water at 9 bars of pressure without generating 20 bars at the pump. Or,
- It’s a premium coffee maker with specific pressure regulators for increased control.
If it’s indeed a premium grade 20 bar espresso maker, then you will find options to control the exact pressure which will be delivered at the brew head. Some coffee beans require more than 9 bars of pressure to initiate flawless percolation and a premium 20 bar machine should have predefined settings to let you know exactly how many of those 20 bars you will need to use for delivering the adequately pressurized water to the head.
Consider if the beans need to be percolated with hot water at 12 bars of pressure, the marked setting will automatically pump the necessary pressure with a buffer in the calculation. It could be pumping 17 bars into the water, but by the time the pressurized water reaches its brew head, it will carry only 12 bars of pressure in it. Therefore, you may not need a 20 bar espresso machine, but some of these high-end products are perfect for those that like to experiment with their brews and beans.
If you are buying a new 20 bar or 15 bar espresso machine, make sure that it comes with overpressure valves (OPV). They serve the all-important purpose of pressure regulation. For example, an OPV will not let the pressurized water through, unless it is carrying a minimum pressure of 9 bars. A secondary valve may also be there to stop the flow of water if it exceeds 9 bars of pressure. The over pressure valves are critical for making that ideal pot of espresso and the setting can be changed from 9 bars to whatever pressure regulation suits your desired concoction.
If you’d like to start making espresso without an expensive machine, consider a normal drip coffee brewer. This won’t be the exact same as a machine espresso but it gets the job done in a pinch. You can also experiment with different flavor additions to make your regular espresso a bit more interesting.
About the author
Jennie Backteman
I´m a ultramarathon runner, landscape designer and a coffee lover.
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