What are pressure bars for?

Coffee maker pressure bars are one of the parameters that attract the most attention from new – and not so new – coffee maker users and buyers. In today’s article, we would like to clarify what exactly pressure bars are, what a bar in a coffee maker means, what they are for, what effect they have on our coffee and whether they are really worth looking at so much.

Let’s start with what we all more or less know: most domestic espresso machines (both pod machines and manual machines such as automatic espresso machines) work with a 15 bar pressure pump. This could be considered the standard measure on the market. We will see later on why they usually have 15 and not another figure. However, there is a small group of coffee machines that work at a higher pressure: 19 bar. These include Nespresso machines or some high-end machines such as the VeroAroma 700 from Bosch.

Now we come to the next question, why do we want these 15 bars of pressure in our coffee machine? If we do not know what the bars are for, it isn’t easy to gauge their importance as future purchasers of an espresso machine.

How do the pressure bars influence our coffee?

In order to understand what influence the pressure bars of the coffee machine have on the result we will obtain in the form of espresso, it is important first to understand how an espresso machine works.

In a nutshell, water in espresso machines is heated to high pressure and then filtered through the ground coffee. The water, which is very hot and strong, immediately extracts all the nuances of the coffee and concentrates them into a drink we call espresso. Espresso coffee is usually short, intense and has a certain creaminess. These qualities are determined by the method of extraction (that’s why a coffee prepared with an espresso machine has different qualities to coffee prepared with a filter coffee machine or a piston coffee machine), and for the same reason, the higher the pressure – the more bars – the more creamy and intense the espresso.

All this happens in theory because, in practice, there are other parameters that also influence these results: the more or less coarse grinding, whether the coffee is heavily or lightly pressed in the filter, etc. Not everything depends on the pressure bars.

Given that the higher the pressure, the better the cream (although other parameters also have an influence), does this mean that the better the cream, the better the espresso? Obviously not. They are different things. If we over-pressurise, the coffee will have properties that are not pleasant to the palate. So what is the break-even point? Let’s look at this in the next section.

How many bars of pressure is necessary to prepare an espresso?

This is the big question.

We know, roughly speaking, that the more bars of pressure our coffee machine has, the better properties we can achieve in our coffee, but how many are really enough? 15 bars? 19 bars? Well, the answer is neither one figure nor the other. The number of bars sufficient to make a real espresso is nine, 9 bars!  And we don’t say this; you can read it in the official certification that determines the qualities of an authentic Italian espresso: Parameters required to make a certified Italian espresso (page 7 of the document).

In the certification, you can clearly read that the water inlet pressure must be 9 bars, with a margin of error of 1 (one bar) above or below. No higher or lower pressure is required to prepare an espresso. And this 9 bar figure has not been put at random; the committee that determines these parameters has arrived at it after a great deal of testing and trial and error experiments: 9 bar pressure is ideal and sufficient for making espresso.

You can also see, in passing, other very interesting characteristics such as the extraction temperature (88º C), the temperature of the coffee in the cup (67º C), the percolation time (25 seconds) or the amount of caffeine, which should not exceed 100 milligrams per cup. Following these premises, the certification is telling us that to prepare a real Italian espresso; we must let 25 millilitres of water at a temperature of 88º C for 25 seconds pass through the filter with the ground coffee at a pressure of 9 bars.

OK, fine, but then, why do most domestic espresso machines have 15 bar pressure instead of 9?

Well, the answer to this question lies in the type of pumps used by domestic coffee machines to generate the pressure, which is very different from the pumps used by professional coffee machines.

How is pressure distributed in a coffee machine?

In espresso machines, pressure is generated in three main ways: two depend on a motor, and a third is completely manual.

  • Catering coffee machines use rotary pumps, in which the water flow is independent of the pressure. They can use more or less liquid, the pressure will always be constant (9 bar).  Translated, this means that they can serve many more people – great flow – without the pressure being affected in the slightest. In fact, they are capable of generating much more pressure, but they are automatically controlled so that they do not exceed the standard figure of 9 bar, which is what the espresso canons command. See if this is important!

Ulka EX4 230 V Espresso machine water pump Automatic coffee machine

  • Domestic coffee machines use vibrating pumps because they are much cheaper. In this type of pump, the pressure depends inversely on the flow of water used. The more water, the less pressure it is able to send. So a much higher initial pressure (15 bar, or up to 19 bar) is applied to ensure that the filter with the ground coffee actually receives the 9 bar we need, and does not get lost along the way.
  • There is a third method of pressure, which does not rely on a pump or internal motor, but is executed manually: the lever or the piston. There are hardly any examples of this – very old – technology on the market, but the most notable are undoubtedly the La Pavoni coffee machines. Here the pressure depends on the skill and the arm of the user who operates the lever up and down.

In the following SeattleCoffeeGear video, you can see a rotary pump and a vibrating pump being broken down, piece by piece, so that you can see the differences between the two:

Why do domestic coffee machines have 15 or 20 bars of pressure, if you only need 9 to make an espresso?

The answer is contained in the previous section, but we detail it here so that you can better understand how these machines work.

A real espresso is made with 9 bars.

Catering coffee machines, by using rotary pressure pumps, are able to generate this 9 bar pressure constantly without loss.

Home coffee machines, on the other hand, use other, more economical piston-operated pumps. These pistons move back and forth, sucking up the water on the one hand and compressing it on the other. And because it is not a constant movement, when the piston moves back, the pump loses pressure.

This is why they work at a higher pressure (15, 19 or 20 bar): to compensate for this loss and to ensure that the 9 bar needed to extract the coffee is reached.

This extraction process is, of course, much less precise than that achieved by rotary pumps (bar pumps), which is why coffee machines in the catering trade are able to extract coffee with many more nuances and generally with better taste.

Conclusions: Are pressure bars important?

In short: the standard pressure for making an espresso is 9 bars, not 15 or 19 or any other figure. Domestic coffee machines incorporate overpressure valves to their pumps (vibratory type) to achieve the final pressure of 9 bars since, due to their operation, these pumps dissipate several bars of pressure during the process.

In short, is this clear to you? Once we know these details, consumers are much more aware. They know how to calibrate better the aggressive advertising campaigns of coffee machine manufacturers, who always try to get the message across that the more, the better.

A 19 bar coffee machine is a guarantee, but it does not necessarily produce better coffee than a 15 bar machine, nor does a 15 bar machine produce better coffee than a 9 bar machine. They are all set up so that the water pressure as it passes through the ground coffee is as close as possible to those 9 bars of reference. And this is without taking into account other much more important aspects such as the quality of the grind, the raw material used, the pressing of the beans, etc. If you neglect any of these issues when preparing your espresso, rest assured that the pressure bars will not come to your aid.

We, therefore, believe it is important to disseminate as much objective information as possible about pressure bars, their function and effects, and thus prevent them from becoming a common marketing tool for manufacturing companies.

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