Espresso Brew Pressure Explained

Brew Pressure - what it really means and how to use it to make fantastic coffee.

Have you been eyeing off that pressure gauge on your espresso maker and trying to hit that magic 9-bar number you hear thrown around in coffee circles all the time?

That's right! It's time to talk about brew pressure. A subject that can be heavily featured and discussed, yet often misunderstood. Like always, we’re here to break it down for you so you’ll be brewing great coffee and getting that perfect shot in no time. Most importantly, we will have you understanding your coffee extraction and brewing pressure, so you, the home barista, can perfect that cup and repeat it consistently. Keep reading!

 

 

What is brew pressure?

When we say brew pressure, we’re referring to the pressure the brewing water being pushed through the coffee grind by the espresso machine, during the extraction.

Traditionally, it is said that 9 bars of pressure is the ideal pressure to extract the perfect shot of espresso. It needs to be understood, that pressure is a derivative of other aspects of the brew process. This means the pressure is directly affected by other variables, in this case, water flow and the resistance created by the coffee grounds/coffee bed.

To put it in a simple formula;

Pressure = Flow / Resistance or Pressure is equal to flow divided by the resistance.

Now that we know pressure is directly affected by both the key elements flow and resistance, it can be understood that it is only PART of the extraction equation.

While we should monitor pressure by feel or a gauge, achieving 9 bar (like often said) is not the make or break of a great espresso. Instead it is another variable we can control and manipulate to tailor our espresso to our personal preference and hit that sweet spot.

  

How does brew pressure affect the extraction?

It’s true, espresso needs pressure to extract. It really can't be espresso unless it is brewed with both heat and pressure. Where the confusion comes in, is how much pressure is required to generate both crema and a great tasting espresso.

Surprising to many people, 4-6 bars of pressure is sufficient to produce espresso, not the 9-bars of brew pressure you often see talked about.

Brewing at the pressure of 9-bars can produce tasty shots of coffee, no doubt! Yet higher peak pressures can also exploit weak points in the coffee bed, creating channels and harsh flavours in the cup. Reducing the brew pressure down to around 6-bar can help improve consistency between shots and reduce the chance of channelling, creating more even, efficient and tasty espressos over a range of shots.

We carried out some extraction tests at both 6 and 9 bars of pressure over 25-30 seconds to give you an idea of the differences we noted. Using a refractometer to measure total dissolved solids (TDS) and in turn extraction yield (EY), the finding of 20 shots each, pulled with the same coffee, equipment, recipe and preparation was surprisingly very similar.

- Both the 9 bar shots and the 6-bar shots fell in an acceptable extraction range of 18-22%.

- The 6 bar shots had a lower standard deviation than the 9-bar.

- The mean (average) of 9-bar extraction yield, was lower than that of the 6-bar extraction.

This gives us an indication that both 9-bar and 6-bar espresso extractions give similar results. The 6-bar extractions were slightly more efficient and consistent. This lends to the theory that reducing the pressure on the coffee puck helps to even water saturation and reduce channelling within the coffee bed.

We can also see that while figures show how much we are extracting from the coffee bean, it is not a good indicator of flavour.

Both 9 and 6-bar brew pressure produce tasty shots, both for milk and black coffee. The trend overall was the 6-bar shots were more rounded, higher clarity and with more perceived sweetness. The 9-bar shots tended to have a more noticed astringency and acidity across the range, but also with a more syrupy body.

 

 

How to change your brewing pressure.

As we covered above, brew pressure is directly related to water flow and resistance. We can execute pressure profiling (change the amount of brewing pressure we use on a manual brewer) by increasing how hard we press our lever - increasing/decreasing the flow of water. We can also increase brew pressure by grinding our fresh coffee beans finer, or by increasing our ground coffee dose (increasing resistance).

There are more advanced versions of pressure profiling and manipulation like grinding your coffee beans much finer than normal, applying pressure and holding it on for a 20-30 second pre-brew. This will help reduce water flow resistance in the coffee puck by lowering the pressure, coupled with a gentle consistent water flow for the rest of the extraction, which can produce some incredible shots. This technique takes practice and patience and ends with a shot time closer to 90 seconds (30 seconds of this would be a pre - infusion).

What brew pressure should you extract at?

With the above knowledge, you can now decide what works best for you. A large range of pressure in espresso brewing can work for extraction from the coffee puck, so if you are chasing a higher body and using an easy to extract coffee, reaching 8-9 bars can help produce that thick syrupy taste, on the flip side, it can expose imperfections in your espresso puck prep.

If you chase higher clarity, a more balanced, rounded and consistent espresso, I recommend reducing your pressure to around the 6 bar realm. The reduced pressure helps with even water flow and produces a beautiful shot, especially if you drink your coffee black.

As your confidence grows with manipulating pressure, you may find it best to hit 9-bars and decline pressure throughout the brew. This helps achieve the best of both worlds.

 

 

What if I don't have a pressure gauge?

All is not lost! You can get a pretty good idea from feel! In fact, I find feel and instinct, the best method for manual brewing.

We will give you the hot tip, if you are not exerting maximum pressure on that lever, you probably aren't hitting 9 bar and that's ok! If you ask us here at team Newton, we tend to land in the 6 - 6.5 bar camp for most of our shots - applying moderate pressure on the lever.

Actually, chasing a fixed number for pressure can be counter intuitive. This can be a downside of pump driven machines. Because the pump pressure tries to stay at the set 9-bars of pressure as the shot reaches the last part of extraction and the puck degrades causing a resistance drop and therefore pressure drop.

The pump needs to increase flow to stay at or close to the set brew pressure and this can increase channels and over extract parts of the coffee bed. The best technique in this situation is to decline water flow and reduce the pressure, to allow a more even extraction. This is best done by feel.

Use your feel, use your instinct, use your gauge. Practice and take note of how much pressure you apply. Before you know it, it will be second nature!

Final thoughts

We get asked about pressure a lot! Sometimes I think too much.

Brew pressure is only part of the equation, along with coffee grind, coffee dose, hot water temperature and extraction yield. There is no magic number for pressure, just like there is no magic number for grind size or extraction time. They all work together in an intricate balance to create that perfect espresso shot.

To produce great espresso consistently takes some understanding of all of these aspects and lots of practice. If you have followed along with our topics so far, you will start to have a really good understanding about getting the best results. The more you taste with intent and take note of how different elements of the extraction affect flavours, the better your coffee will be.

Enjoy the journey that coffee brings, none of us have made it all the way to the end yet.

Until next time.