Pressure Profile for Espresso

Espresso Pressure Profile: 3 months

We are now 3 months in. Using the La Marzocco Strada EP has been a complete game changer for our shop. We will continue to update our findings as we begin to explore the possibilities of this machine. All of our experience to this point is based on subjective observations, not scientific measurements. Let’s look at our current pressure profile.

In this series of articles, we plan to be completely open about our findings in the hope that other shops and coffee aficionados will be able to learn from our experience. We welcome comments and input that may counter our experience; we can all learn more about espresso and pressure. Let’s push the limits of coffee.


Coffee and Pressure Extraction Principals

When we discuss extraction in filter coffee, we rarely touch on the influence of pressure as an extraction variable. With little deviation from the normal brewing process, pressure is determined by gravity. Elevation plays a role, but compared to espresso pressures that difference is negligible. Most filter coffee extractions take place at 1 Bar at sea level. The standard espresso extraction takes place at 9 bar. For an explanation of the 9 bar standard, see our previous post on the Strada.

Filter coffee and espresso are two completely different beasts. However, for all of their differences many of the principals are the same. Pressure increases extraction, therefore espresso extracts far more efficiently than filter coffee does. There are many variations in brewing parameters between espresso and filter coffee that we won’t cover here (grind size, contact time, water temperature, water quality, etc.) Our focus in this article is to speak exclusively about the pressure changes, and how they relate to espresso flavor and quality.

Why 9 Bar?

We briefly covered the history of espresso in the prior blog post about the Strada EP. Suffice to say that with the advent of rotary pump machines, we needed to choose one constant pressure to use as a standard. Moving from the lever-action machines, the common thought was to find an average pressure. If the lever-action machines started infusion at 3 bar, moved up to 10 bar, then gradually reduced to 6 bar throughout the shot, perhaps 9 bar was the sweet spot! While this may hold true for the most part it eliminates a lot of variables, good and bad.

For well over a decade, the professional espresso community has been questioning the nearly global acceptance of a 9 bar standard pressure. Many have played with higher extraction pressure, and there has been a large push for lower extraction shots as well. With the introduction of variable pressure machines, the coffee community suddenly had the tools to experiment and learn.

While these pressure profiling machines were certainly advanced, they were dependent on the barista adjusting the pump pressure exactly the same every time. An excellent and dedicated barista could likely accomplish this with some consistency, but how do you replicate this across an entire staff? There were certainly limitations with this process. The advent of the Strada EP allowed for complete programming. A tech could experiment with different pressure profiles, and record the results digitally. They could then determine the optimal profile, and program the machine to repeat the recipe with perfection.

Yeah, great. So what does it all mean?

In the 3 months that we’ve had our hands on the Strada EP, we have found some similarities with the espresso that we’ve brewed. Please remember, at this point these are strictly subjective results, but we have been able to completely change the face of our espresso program. So let’s dive in.

First, a quick look at a standard espresso profile (using the Strada editing software).

Standard Espresso Pressure Profile

Standard 9 Bar shot

This graph shows the barista switching the machine brew cycle on. The water pressure starts at 0 Bar, ramps up to 9 Bar, and stays steady until the machine is switched off. This has been the standard since the advent of the rotary pump espresso machine.

Now let’s take a look at one of our espresso offerings, Ethiopian Sidama Natural. We find that it responds best to a slight pre-infusion, with a sudden ramp to 10 bar and a gradual reduction to 4 bar throughout the brew. This results in a sweet, fruity and medium bodied espresso. With a long and sweet finish, the fruit notes are more pronounced but not overwhelming. It is currently the preferred espresso in our shop.

Sidama Espresso Pressure Profile

Our Strada EP profile for a Natural Sidama

Sidama: 9 Bar vs Custom Profile

The only way to truly begin to understand the difference between one pressure profile and another is to constantly experiment with different profiles. Believe me, on more than one occasion we drank espresso until we were sick. In order to limit our discussion to a resonable length, we plan to cover our successes, and the generalizations that seem to hold true with pressure as a variable.

So how does our custom pressure profile differ to the standard 9 bar extraction? Significantly. When we use the standard 9 bar profile (and a 2:1 ratio) we encounter a lot of woody tannins. In order to avoid this, we are forced to grind finer to find fruity acidity. By grinding finer, we are forced to sacrifice the long sweet finish that is otherwise possible.

Introducing the pressure profile, we quickly discovered a trend that can’t be ignored. Introducing high pressure up front results in an acidic cup that is explosive in flavor. When we stay in that high pressure longer, the acidity is noticeably more pronounced. When we push at high pressure across the entire extraction, the tannin flavor is MORE pronounced.

Too long; didn’t read

The results tell us subjectively that acidity can be enhanced with high pressure, but only to a limit. Beyond that limit, extraction becomes undesirable and unpleasant.

Our next observation deals with the middle region of the shot. If we back off of the high pressure peak quickly, we can extend the middle portion of the shot. This extends extraction and allows for the sweetness to pop.

With our Sidama, the most desirable pressure profile is a slow infusion, with a sudden ramp up to a 10.5 bar pressure. Immediately after hitting this peak, we back down in a slow but steady fashion to a 3 bar finish.

This marries the best of both worlds: a beautiful fruity acidity, followed by a long sweet finish. Most guests drinking this espresso neat won’t even touch their sparkling water. We’ll call that a win, for sure.