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Espresso Coffee Pressure Profiling
Application of Pressure Profiling
Application of Pressure Profiling

Application of Pressure Profiling

At first glance, espresso coffee pressure profiling introduces a seemingly infinite number of possibilities which has the potential to overwhelm all but the most fanatical coffee enthusiast. It is correct to say that the possibilities are numerous, but this should not be considered a barrier in understanding the fundamental principles of pressure profiling. Once these principles are understood, it is possible to simplify the infinite possibilities and group them into specific base profiles.

After a considerable period of testing, it was discovered that optimum extraction from a given coffee, or more accurately the most preferred flavour, was produced from a variation of one of four base profiles. Once this was realised, more attention was given to understanding each of these four profiles. This page is dedicated to explaining these profiles.

The Four Base Pressure Profiles

1.      Conventional

2.      Continuous Slow

3.      Short Stop

4.      Long Stop

Each of these profiles is explained below.

It is likely that more base profiles will be added in time, but to date these four have proven to produce exceptional results. Some coffees work well with all four whereas other coffees do not. It is interesting to note that it is possible to extract quite different flavours from the same coffee by using a different profile. Most people would have only experienced espresso extracted with the conventional profile, and remain unaware of the full spectrum of flavours on offer.

Mastering each of these profiles will certainly add a new dimension to your coffee experience, and it is only a matter of time before pressure profiling capabilities become a standard feature of espresso equipment.

Equipment and Technique

All research has been conducted with the Rossa and Rossa HC Hand Espresso fitted with the Pressure Adapter. The descriptions below are written to help users of the Portaspresso System to build proficiency in pressure profiling, and the relating video clips are added to provide visual aid.

However, the profiles and their explanations apply equally to any machine or device capable of controlling the applicable variables.

Each video clip shows the complete operation from fitting of the filter head through to the end of extraction. The 10 bar pressure gauge fitted to the Pressure Adapter used for the videos is larger than standard and is fitted at an angle to provide a clear view to the camera.

Prior to filming each of the shots, the coffee was ground with the Rosco Mini Hand Grinder immediately before extraction, the filter head was preheated, the coffee tamped into the filter head securely and squarely (Note that tamping needs to be of sufficient force to prevent the puck from dislodging as it is fitted to the Rossa), and the Rossa was preheated as per the instruction manual to achieve 92 – 93 Degrees C.

For reference, 18 grams of the same coffee ground to the same size was used for each shot, and each shot was visually identical. It might not be clear in the video clips, but each shot is 100% crema at completion of extraction. The crema settles out to approximately half the shot’s volume, and would continue to settle out further if given enough time.


Conventional Profile



Conventional Profile Video Link

The conventional profile is the standard used by the majority of both domestic and commercial espresso machines. It has proven the test of time as it produces fast, consistent and high quality espresso. It is characterised by minimal pre-infusion, an upper pressure of 9 bar, and an extraction that produces approximately 30 to 40 ml of espresso in approximately 25 seconds from commencement of flow. It is arguably the most forgiving profile because its timing is relatively condensed and the high pressure tends to produce a more blended shot which can mask some unwanted flavours. Mastering this profile is essential for those exploring the seemingly infinite possibilities of profiling as it provides a standard from which experimental shots can be compared.

Pre-infusion

The key to producing a good conventional profile with the Rossa Hand Espresso is to minimise the time it takes to pressurise the puck. The example shows a pre-infusion period of 4 to 5 seconds, which is a consequence of the time it takes to compress air trapped in the cylinder chamber. Minimising this period is essential for preventing over-extraction.

Pressure Ramp-up

The ramp-up duration is rapid, but careful attention is required in order to control the flow rate once the upper pressure is achieved. Slow ramp-up allows more soaking of the puck which produces a high flow rate once upper pressure is reached, whereas a fast ramp-up minimises water penetration into the puck which slows the flow rate. Taking note of the ramp-up speed to approximately 5 bar provides the feedback necessary to enable the crank speed to be adjusted to achieve the desired extraction flow rate. For example, a fast ramp-up to 5 bar requires a slowing of the crank speed for the remaining ramp-up, whereas a slow ramp-up to 5 bar requires an increase of crank speed for the remaining ramp-up. Determining what is fast and what is slow requires experimentation. There should be no pause at 5 bar. It is an approximate pressure used for descriptive purposes. The ramp-up profile should be continuous and relatively fast.

Upper Pressure, Ramp-down and Lower Pressure

The upper pressure for this profile is typically 9 bar, but plus or minus 0.5 bar generally has little effect. The example shown has an upper pressure of 9.4 bar with a steady ramp-down to just above 8 bar. There should be no distinct ramp-down. The ramp-down is achieved by maintaining a steady and consistent stream, which typically requires a gradual reduction of pressure as the puck’s flow resistance decreases. Crank speed is generally held constant, but pressure will gradually go down as the puck’s resistance decreases.

Notes

Total extraction time from the start of flow is approximately 25 seconds, but this time can be altered by grind size and ramp-up speed, or both. The key to a good conventional profile is minimal to no pre-infusion; longer pre-infusion risks over-extraction. (As a general rule, the longer the pre-infusion, the lower the extraction pressure).

A common problem encountered with this profile is an unintentional extension of pre-infusion, which causes a high flow rate and generally an over-extracted shot. This is often wrongly compensated for by using a finer grind, which introduces other factors and potential problems. It is important to take note of the time it takes from initial water contact (the moment the Rossa is inverted) to the point at which enough pressure is generated to start moving the gauge needle. If small doses of ground coffee are used, more air will be trapped in the cylinder chamber due to the larger space in the filter basket left void of coffee. The remedy is to use a smaller basket or fill the device with more water.

For reference, using the same grind size and tamp pressure in the standard filter basket, it is possible to use as little as 12g of coffee to produce a shot that looks identical to a 22g shot. The key is to apply pressure quickly before the water soaks into the puck too far. It is possible to extract a 30 to 40 ml shot from 12g of coffee that is all crema on completion of extraction. It will settle out at much the same rate as a standard shot. When performed correctly, taste is the only noticeable difference.



Continuous Slow Profile



Continuous Slow Profile Video Link

The continuous slow profile is characterised by a continuous and slow blending of pre-infusion and ramp-up followed by a similarly slow extraction period. The extraction speed is similar to most profiles, but the period prior to commencement of flow occurs at a similar speed as extraction. Upper pressure is generally between 5 to 6 bar, and extraction is approximately 20 seconds from commencement of flow which should occur between 2.5 to 3 bar. This profile provides a very smooth pressure build-up and seamless transition into the extraction period. It works well for isolating specific flavour characteristics in coffees that do not respond well to a pause during pre-infusion.

Pre-infusion

The pre-infusion period (duration from initial water contact to first movement of gauge needle) is typically between 10 to 15 seconds. There is no pre-infusion pause.

Pressure Ramp-up

The ramp-up duration is generally between 10 to 15 seconds, but commencement of flow should occur between 2.5 to 3 bar. Ramp-up speed should be adjusted in response to the pressure at which flow commences. For example, if it occurs at 2 bar, speed should be slightly increased. If flow does not emerge after 3 bar, speed should be slowed. The aim is to control the ramp-up speed so that the upper pressure is achieved with a flow rate that requires little or no change in crank speed.

Upper Pressure, Ramp-down and Lower Pressure

The maximum extraction pressure should stay within 4 to 6 bar, but is typically between 5 to 5.5 bar. An upper pressure above 6 bar following the long pre-infusion period generally produces an over-extracted shot. Once the upper pressure is achieved, speed should be maintained relatively constant throughout extraction. Flow rate should be maintained, which requires allowing the pressure to slowly ramp down. Note that when using low upper pressures (for example 4.5 bar), crank speed often needs to be steadily increased to prevent the lower pressure from dropping below the 4 bar threshold.

Notes

When varying the upper pressure, the pre-infusion / ramp-up period should be adjusted in response. For example, an upper pressure of 6 bar requires a shorter pre-infusion / ramp-up period, whereas an upper pressure of 4.5 bar requires a longer pre-infusion / ramp-up period. There will be a sweet spot between under-extraction and over-extraction that can only be found through experimentation, and this point generally varies dependent on the coffee and its particular roast.



Short Stop Profile



Short Stop Profile Video Link


The short stop profile is similar to the continuous slow profile, but with the addition of a distinct pre-infusion pause. The pause is generally held at 0.5 bar, which enables water to gently soak into the puck and individual coffee particles further than with the continuous slow profile. Upper pressure is generally between 5 to 5.5 bar, and extraction is generally between 15 to 20 seconds from commencement of flow which should occur between 2.5 to 3 bar. This profile draws out and isolates the nutty characteristics of a particular coffee, but is not suited to all coffees.

Pre-infusion

Pressure is ramped up to approximately 0.5 bar at which time a pause is held. The typical short stop pause is about 5 seconds. Variations can be made by increasing or decreasing crank speed prior to the pause.

Pressure Ramp-up

The ramp-up duration is relatively fast and is generally under 10 seconds. Similar to the continuous slow profile, commencement of flow should occur between 2.5 to 3 bar. Ramp-up speed should be adjusted in response to the pressure at which flow commences. For example, if it occurs at 2 bar, speed should be slightly increased. If flow does not emerge after 3 bar, speed should be slowed. The aim is to control the ramp-up speed so that the upper pressure is achieved with a flow rate that requires little or no change in crank speed.

Upper Pressure, Ramp-down and Lower Pressure

The maximum extraction pressure should stay within 5 to 5.5 bar. An upper pressure above 5.5 bar following the extended pre-infusion period generally produces an over-extracted shot. Once the upper pressure is achieved, speed should be maintained relatively constant throughout extraction. Flow rate should be maintained, which requires allowing the pressure to slowly ramp down. Pressure generally does not drop rapidly with this profile. The pause tends to consolidate the puck, and the relatively fast ramp-up further restricts the flow. The lower pressure should not drop below the 4 bar threshold.

Notes

The upper pressure of the short stop profile generally stays within a small margin. Variations can be made by increasing or decreasing crank speed prior to the pause, and also experimenting with various grind sizes and ramp-up speed combinations. Finding the sweet spot between under-extraction and over-extraction is more complex with this profile due to the extra variables, but it should not be difficult. Taking careful note of what is changed to produce a specific taste makes it very easy to reproduce the same profile and relating variables.



Long Stop Profile



Long Stop Profile Video Link

The long stop profile is a variation of the short stop. It has a distinct pre-infusion pause, but for a longer period. Due to the extended pre-infusion period, the upper pressure is less. The pause is generally held at 0.5 bar, which enables water to gently soak into the puck and individual coffee particles. Upper pressure is generally between 4 to 4.5 bar, and extraction is generally between 15 to 20 seconds from commencement of flow which should occur between 2 to 2.5 bar. Similar to the short stop, this profile draws out and isolates the nutty characteristics of a particular coffee, and highlights certain flavours that often go unnoticed. This profile is not suited to all coffees, but it should be tried because the extended pre-infusion pause sometimes works when the short stop does not.

Pre-infusion

Pressure is ramped up to approximately 0.5 bar at which time a pause is held. The typical long stop pause is about 10 seconds. Variations can also be made by increasing or decreasing crank speed prior to the pause.

Pressure Ramp-up

The ramp-up duration is relatively fast and is generally under 10 seconds. Due to the extended pre-infusion, water soaks further into the puck which causes the commencement of flow to occur at a slightly less pressure than with other profiles. It generally commences between 2 to 2.5 bar. Ramp-up speed should be adjusted in response to the pressure at which flow commences. For example, if it occurs below 2 bar, speed should be slightly increased. If flow does not emerge after 3 bar, speed should be slowed. The aim is to control the ramp-up speed so that the upper pressure is achieved with a flow rate that requires little or no change in crank speed.

Upper Pressure, Ramp-down and Lower Pressure

The maximum extraction pressure should not exceed 5 bar. Best results are generally produced at 4.5 bar. An upper pressure above 4.5 bar following the further extended pre-infusion period risks an over-extracted shot. Once the upper pressure is achieved, speed should be maintained relatively constant throughout extraction. Flow rate should be maintained, which requires allowing the pressure to slowly ramp down. Note that when working with these low upper pressures, crank speed often needs to be steadily increased to prevent the lower pressure from dropping below the 4 bar threshold.

Notes

Due to the extended pre-infusion period, best results are produced from relatively low extraction pressures. An extraction pressure as low as 4 bar has shown to produce exceptional results with some coffees, and there should be no visual difference between shots produced by either 9 or 4 bar.

The low extraction pressure of this profile limits the effects of varying ramp-up speed. Variations are generally made by increasing or decreasing the pre-infusion pause. Similar to the short stop profile, finding the sweet spot between under-extraction and over-extraction is more complex with this profile due to the extra variables, but it should not be difficult. Taking careful note of what is changed to produce a specific taste makes it very easy to reproduce the same profile and relating variables.