2 Reasons Why The Correct Pressure is Important For Espresso


Mastering the richest espresso is a never-ending journey, but it keeps the coffee-making experience interesting. One of the first things you need for a quality espresso is finely ground coffee beans; the second is the correct tamping method and third the correct water pressure through the portafilter.

The correct pressure is essential to guarantee consistency and quality every time you pull a shot. For the right pressure, you need a minimum of eight bars of pressure. If you have too high pressure, your espresso will be over-extracted and bitter; if you don’t have sufficient pressure, your espresso will be weak and under-concentrated.

In this article, we will explore how pressure affects espresso. We will expand more on the correct pressure for your machine and what to do if your pressure is too low.

How Does Pressure Affect Espresso?

The correct pressure in an espresso machine produces consistently good results every time you pull a shot of espresso.

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We touched on how too low pressure can weaken your espresso because it’s under-concentrated, and too high pressure can make your espresso taste bitter and over-extracted.

When coffee beans are ground and placed in the portafilter, much of what happens after can seem mysterious. Still, it’s essential to think of what is happening to make adjustments if necessary.

Hot water on its own does minimal compression; its density and viscosity are consistently at stable temperatures.

To expand on that, the flow of water molecules that pass through an orifice is predictable, but you can accurately calculate flow if you can measure the pressure on either side of an orifice.

Pressure needs two things to function – 1) a device to generate the flow of water (the pump), and 2) a device downstream to stop it.

The pump’s power to move the water and the resistance it meets downstream determine the level of pressure in the system. Without restriction, there is no pressure.

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Espresso machines control pressure in a couple of ways. Firstly, the pump regulates water pressure to a set value, usually a none bar; ensure the inlet water pressure doesn’t go above that value.

It must be standardized to a fixed point from which other values are calculated. The pump uses a spring that regulates pressure under tension.

The tension adjusts to keep a consistent pressure regardless of flow. Nevertheless, the motor and the pump must keep up with the demand for frequent use.

Secondly, the group jet is a mechanism that also helps control pressure. The jet offers enough resistance for the pump to maintain a nine-bar on machines with many groups.

If the machine didn’t have jets, flushing a second group could decrease the system’s pressure enough that other groups cannot adequately extract espresso.

There are other resistant mechanisms like pathway and diffuser plates in a group, a small tube, a solenoid valve orifice, and flowmeters – though not all espresso machines have them.

However, until you place the portafilter in the machine to brew, jets are critical to regulating flow and pressure.

Lately, there has been some interest in using different flow rates to control coffee extraction rather than pressure.

However, the issue at hand is if the flow going into the cup is evidence of good extraction or if regulating the flow may have the same effect.

With pressurized portafilters and pods, the pressure seems to be an essential function. You need the right pressure to break through the coffee’s cellular walls and extract the perfect brew with a rich aroma and delicious crema.

What Is The Best Pressure For An Espresso Machine?

When searching for an espresso machine, you may notice that one of the features advertised is the machine’s bar pressure rating. The bar indicates how much pressure is used to push water through ground coffee in the portafilter.

Bars measure atmospheric pressure, whereby one bar equals the amount of pressure at sea level. Nine bars is nine times the pressure amount at sea level.

The industry standard recommends nine bars to brew espresso. Generally, seven to nine bars are correct for pump-driven machines.

There is a popular notion that bigger is better when it comes to the pressure of brewed coffee, but be aware that anything over ten is unlikely to enhance the espresso’s quality.

Some machines can push out higher pressure levels, and they can help the user brew a better espresso than a machine that only pushes out nine bars. However, much depends on the grind, the portafilter’s size, and how old the machine is.

Many machines promoting a higher bar pressure produce a low bar when the machine is in use. Substandard machines tend to deteriorate faster, and the bar pressure decreases over time as parts wear out.

It’s more important to know what you’re doing with a nine-bar espresso machine than to own a fifteen-bar machine and use it incorrectly.

Pump and rotary machines work better than steam-driven machines. These espresso machines use an internal broiler that heats water which in turn builds steam pressure.

This pressure is pushed through the coffee grounds by using its own force. The optimal brewing temperature is 200 degrees Fahrenheit, but steam-driven machines often brew coffee at hotter temperatures, making the shot taste burnt and over-extracted.

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With pump and rotary machines, you don’t have this issue, as the water inside is heated with a heat exchanger or a broiler to the optimum temperature.

Once the machine has reached the right temperature, it pumps water through with great force pulling the perfect espresso shot each time.

Pump and rotary machines can pump with as little as eight bars of pressure and produce excellent coffee.

How Do I Increase The Pressure On My Espresso Machine?

You may be worried that your machine isn’t building enough pressure and that the gauge is lower than nine bars.

When your pressure is low, your shots will flow too quickly, leading to various flavors that might be less than pleasing. You need to stop looking at the pressure gauge and get out your scale and stopwatch.

You need to verify if your coffee grounds are fine enough that your 18 to 20-gram dose puts out 30 grams of liquid in 25 to 30 seconds.

A well-working espresso pump machine will consistently use nine bars of brew pressure; the gauge can only display this when it meets enough resistance. To check this, insert your blind basket into the backflush disc and activate the pump.

Within about ten seconds, you should see nine bars displayed. Backflushing often shows higher brew pressure so that you could see around ten bars on the gauge.

When you stop the pump after full pressure, the needle often lands at different places since it doesn’t need to rest at zero. Brew pressure gauges only provide the correct information when the pump is in use and meeting enough resistance.

Vibration pumps tend to fail after four or five years of service – this is evident by a change in pitch and having to set the grind much coarser.

If you think your vibration pump requires replacing and your unit has a pressure gauge, backflush, and if your brew pressure is below nine bars, get it serviced.

Rotary pumps function for many years without need adjustment. Be aware that when you switch your rotary machine from reservoir to plumbing setting, the additional pressure may push your brew pressure over nine bars – adjust your brew pressure down slightly.

How Do I Know If I Have Poured The Perfect Shot Of Espresso?

Once you have chosen a delicious roast, learned to perfect your grind, tamp it into the portafilter, and have your machine set at the right pressure, you’re ready to go.

Your espresso should take between 20 and 25 seconds to brew with the initial steps in the correct order.

The espresso stream flowing from the portafilter should resemble that of warm, thick honey, and the resulting shot should consist of a crema thickness of around 1/4″ to 1/3.”

An under-extracted shot will have a non-existent crema with a blonde color. An over-extracted shot will have a thin crema that appears brown or burnt.

Final Thoughts

Much thought goes into making a decent espresso. You may have a delicious roast, a perfect grind, and your tampering may be in point, but if your machine has the wrong pressure (too high or too low), it will undoubtedly affect the taste and appearance of your espresso.

The coffee industry recommends using a pressure of nine bars to extract an espresso shot; there is no need to go for a higher bar.

Learn how to use and maintain the machine correctly, and you can guarantee the perfect espresso shot every time.

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