La Marzocco Strada

There is a new machine on the block, newly released by La Marzocco. You may have heard of the La Marzocco Strada before. This line of machines was created by the “Street Team,” which was made up of coffee professionals, baristas and engineers. A list was made of the most important features to include in a dream machine, and the La Marzocco design team went to work.

Our main focus within the Strada line will be on the pressure profiling technology within the Strada EP, and now available with the latest version called the Strada X. The Invoke crew will have the opportunity to get hands-on with the newly released Strada X later this month, but for the time being this article will focus on the theory behind using pressure as a variable in espresso brewing. Expect an update on this Strada X after we’ve had a chance to kick the tires a bit.

Pressure Profiling

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.

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?

With the advent of rotary pump machines, the espresso world 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?

We’ve had the pleasure of working with, and pulling shots on a Strada EP over the last 6 years, and we have found some similarities with the espresso that we've brewed. So let's dive in.

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

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 a different espresso offering, an 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.

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.