With all the excitement that takes place when new grinders reach the market, specialty coffee’s previous poster child—pressure profiling—seems to have been forgotten. However, with the recent announcement of a single group La Marzocco Strada, and the availability to the home user of other machines (such as the Vesuvius), all of which feature pressure profiling, it’s worth re-examining this technology.
Spanish Version: Manejo de la Presión: La Clave para una Extracción Perfecta
Credit: Antonio Nurri
What Is Pressure Profiling?
Pressure profiling is when a machine varies its pressure at which it pumps water through the coffee puck during extraction. Most machines pump only operate at a single pressure—typically 9 bar—at one time, although there’s sometimes a non-adjustable period at the beginning of the extraction where water is at line pressure (2-4 bar) which is known as pre-infusion.
There are several types of pressure profiling machines available. Some allow any combination of pressures to be used throughout extraction. Others allow pressures to be set in three distinct stages. Others vary the flow rate of the water rather than pump pressure. They’re thought of as offering pressure profiling, but it’s closer to flow profiling.
Lever machines have a very basic form of fixed pressure profiling. The initial pull down of the lever lets water into the grouphead at low pressure, and then the spring that forces the lever back to its original position, producing a rising then declining pressure profile.
Full-pressure profiling machines allow the user to control the pump pressure throughout extraction. A range of profiles are possible, from a slow ramp up and ramp down to the opposite. In practice, however, a particular profile dominates: a long pre-infusion, followed by a ramp up to full pressure, then a declining profile in the last third of the extraction. Most coffee shops prepare espresso-based drinks like this.
Stunning custom La Marzocco Strada 2 group at the London Coffee Festival. Credit: @nowavecoffee
A Typical Profile
With so many different profiles available, why do we typically stick to the same one? This depends on extraction’s three main stages.
1. First Contact
The first stage of extraction involves water coming into contact with dry coffee grounds. On a basic machine, this happens with a lot of force. The consequence of the puck being hit with such force is channeling, where the water finds the line of least resistance in the coffee and causes uneven extraction.
Credit: Jonathan Prestridge
Pressure profiling machine can start with initial low-pressure phase, lasting several seconds, before increasing significantly. This lets the grounds swell and become adhesive, which prevents channeling. It limits the migration of fines, which are an inevitable consequence of a grinder’s bimodal particle distribution. Fines contribute body to a shot, but too much migration of them slows down the flow, causing poor extractions.
2. Increase in Pressure
Pressure increases in the middle phase to reach the chosen maximum level where it stays for several seconds. This is similar to that produced by a machine with fixed pre-infusion, although the ramp up on a full-pressure profiling machine is more gradual to reduce the possibility of channeling.
3. Ramp Down
The final phase is a ramp down leading to the end of the extraction. Lowering the pressure here as the puck density decreases and extraction has already taken place. If the ramp up is long, a consistent flow rate will require a longer ramp down.
This profile suit speciality coffees, since it facilitates a full extraction. The long pre-infusion and ramp up stages enable a finer grind to be used than with a straight 9 bar machine making it easier to achieve optimum yields with light-roasts that are difficult to extract on traditional equipment.
There are some people using vastly different profiles, one of which is three times World Barista Championship finalist and current UK Barista Champion Maxwell Colonna-Dashwood. He runs a relatively long pre-infusion followed by a straight 6 bar extraction on his Sanremo Opera. Maxwell has found that the lower average pressure over the course of the shot mitigates against channeling and produces excellent extractions when used in conjunction with his shop’s Mahlkonig EK43 grinder and 15g VST baskets.
Beautiful custom wooden panel on the Sanremo Opera at Colonna & Smalls. Credit: Jonathan Prestidge
There’s scope for experimentation with new profiles, as Maxwell demonstrates. As grinder technology advances and we understand more about espresso extraction, we can hope pressure profiles will evolve to create even tastier coffee.
Can’t get enough of the beautiful Sanremo Opera. Such an incredible design. Credit: @framework_coffee
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Edited by A. Guerra.
Feature Photo Credit: Coffeetopia (@kahvebarmeni)
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