Introduction to Espresso Coffee Pressure Profiling
By Ross Spencer 17th October 2011
Profiling is an emerging area in specialty coffee that could potentially revolutionise the industry. For many years, it has been considered that optimum espresso extraction is obtained by pumping water heated to about 92°C through a cake of ground coffee at a fixed 9 bar of pressure to produce around 30 ml of espresso in about 25 seconds. The exact values seem to vary somewhat, but the one constant in conventional thinking is fixed pressure, and this is evident in the design of most electrically driven pump espresso machines. Profiling advocates challenge this fixed assumption, and argue that 9 bar is not necessarily the optimum pressure for all coffee blends, and that 25 seconds extraction time does not always produce the best results. The essence of profiling is to not accept conventional parameters, but search for alternative pressure (both fixed and variable) and timing combinations to produce the best possible espresso extraction from a particular coffee.
Even though profiling is a relatively new topic, the fundamentals have been used, possibly by accident, for at least as long as lever machines have been available. The variable pressure used in lever machines is a consequence of their design, and operating these machines in such a way is simply how they are used. It was not until modern pressure profiling machines emerged that people began to focus on and analyse the profiles used in lever machines. As such, it seems that the lever machine’s profile has become a form of benchmark that people aim to replicate.
The availability of information and research on profiling is limited, but this will inevitably change over time as the availability of equipment capable of profiling increases. The aims of this article is to contribute to the pressure profiling knowledge-base by sharing experimentation data and results, as well as attempt to provide an objective standard that will enable others to replicate and compare results. It is recognised that “taste” preferences vary somewhat from one person to the next, but it is anticipated that patterns will emerge over time to reveal consistent and repeatable profiling effects.
It should also be noted that all experimentation is conducted with the Rossa Hand Espresso fitted with the Profiling Adapter. However, the principles and profiling data presented in this article apply equally to all machines and devices capable of controlling and manipulating the necessary variables.
Definition of Profiling
Profiling is typically defined in terms of variable pressure, which is why it is often referred to as “pressure profiling”. However, any comprehensive discussion or analysis of profiling should include all possible variables, including temperature, flow rate, grind size and consistency, coffee roast, and any other variable that influences espresso. Rather than challenging convention, profiling is an extension or improvement on what is already known.
The aim of profiling is to seek the specific combination of variables, whether fixed or otherwise, that reveal or enhance the desirable characteristics of a particular coffee. Profiling will not necessarily make bad coffee taste good, but it does provide more scope or options to discover otherwise hidden or subtle flavours, or to enhance or reduce specific flavours. Therefore, profiling can be defined as the process of seeking the optimum combination of fixed or variable temperature, pressure and timing which produces an infused espresso stream that flows at a rate that produces the preferred characteristics from a particular coffee.
Grind size and quality
Grind size in profiling requires a different perspective than that described in conventional espresso theory. The grind size is selected primarily for the taste it produces, rather than a specific flow rate.
Grind quality is important for all espresso extraction, and is vitally important in conventional machines where grind size is used to control the rate of flow. However, profiling enables a broader range of grind sizes to be used. The grind size remains important, but more so for taste rather than pressure or flow rate. Similar pressure and flow can be obtained from a broader range of grind sizes than that used in a conventional machine by manipulating the pre-infusion and pressure ramp-up profile. This will be discussed in more detail below.
Grind size consistency is crucial for effective profiling. The grind size distribution should have minimal deviation so that water penetrates each particle to the same depth to ensure consistent extraction. Consistency on this variable helps isolate and enhance or soften individual characteristics. A large grind size distribution causes more variation which results in a more blended extraction. This makes it more difficult to isolate certain characteristics, but results can still be of a high quality.
Extraction temperature
The importance of water temperature during extraction is viewed as the most critical factor to some, and quite a tolerable variable to others. Regardless of these views, what is certain is that water temperature decreases to varying levels during extraction. This can easily be tested by measuring the temperature of a shot immediately after extraction.
The temperature drop is caused by lower temperatures of the group-head and the ground coffee puck. Even though it is standard practice to preheat the group-head, it will rarely reach or maintain full temperature. Additionally, coffee is ground at ambient temperature or cooler, which will cool heated water as it works through the puck. The temperature equalisation effect of the cooler group-head and coffee puck will cause the water temperature to drop by varying levels during extraction. The rate of temperature drop is dependent on the equipment used and its method of operation.
Temperature drop does not cause any real problems; otherwise its effects would be more widely discussed. It is recognised that the difference is not of any real significance, and it is raised here for completeness only. However, it is possible to influence espresso taste by controlling the rate of temperature drop in the Rossa Hand Espresso.
All things being equal, the rate of temperature drop can be influenced by varying the Rossa’s preheating procedure. For example, preheating the unit just enough to obtain the desired temperature will have a higher rate of heat loss than when the unit is preheated for an extended period and the water allowed to cool to the desired temperature before extraction. The first preheating method is quicker, therefore less heat penetrates the brass mass. The second method is longer, therefore more heat penetrates the brass mass. Even though the water used for extraction is set at the same temperature, the rate of drop will be less for the second technique. The difference is minimal, and for the record, the author prefers the first technique.
Stages of a profile
The following terms define the various stages of a typical profile. They relate specifically to pressure and timing. Temperature is varied independently of the profile, but all variables and their interrelating effects should be considered.
Initial water contact – The moment that water first touches the coffee puck.
Pre-infusion – The period from initial water contact to commencement of pressure ramp-up. Used to allow water to soak into the coffee puck prior to extraction.
Pre-infusion time – The duration of time from initial water contact to commencement of pressure ramp-up.
Pre-infusion pressure – The pressure used during pre-infusion to enable water to penetrate the coffee puck.
Pressure ramp-up – The rate of pressure increase from pre-infusion to extraction pressure.
Upper pressure – The highest pressure used during extraction.
Pressure ramp-down – The rate of pressure decrease from the upper extraction pressure to the lower extraction pressure.
Lower pressure – The lower pressure used during extraction.
Profiling Equipment
The availability of machines or devices capable of profiling is currently limited, but this is likely to change as more people are introduced to the possibilities that profiling offers. The Rossa Hand Espresso, with or without the Profiling Adapter, is currently the only low cost device capable of controlling the variables to the level required for effective profiling, and is possibly the only currently available device that is capable of manipulating the variables to the level described in this article.
The Profiling Adapter provides more accuracy, and enables objective sharing of data. However, hand profiling with the Rossa is certainly possible for those with good feel. Crank arm turning effort is surprising accurate and repeatable, but it does take some practice to develop proficiency.
How to Profile
It is advisable to begin with a standard extraction using conventional variables. While this is not absolutely necessary, it will provide a reference to which you can compare experimental shots. From here on, there are no set rules. Experimentation is the key, but taking notes is advisable due to the number of interrelated variables.
Setting the Grind
A good starting point for grind size is to begin with the same setting used for the standard shot as described above, and then vary as necessary to find the size that results in the best taste for the particular coffee used. Choose a quality grinder that enables very fine adjustment. The Rosco Hand Grinder’s locknut grind setting adjustment design is ideal for profiling because it enables the size to be set at any point, as opposed to a predetermined index position.
It is possible to use a much finer grind with profiling, but this can sometimes cause a taste similar to a poor quality grind that produces numerous fines. Testing so far has shown that no more fines pass through into the cup between the finer grind and the optimum grind, but the taste could lead one to think otherwise. The key is to find the exact size from which taste begins to deteriorate, and then use a slightly coarser grind setting. If using the Rosco, use a setting about 0.01 – 0.02 mm coarser than the point from which taste begins to deteriorate.
Pre-infusion
The purpose of pre-infusion is to prepare and set the puck by permitting enough water to penetrate the individual coffee grounds in the correct time to achieve the desired extraction characteristics. Pre-infusion occurs at low pressures ranging from ambient pressure (zero gauge reading) to approximately 2 bar. The duration also varies from a few seconds to 30 seconds or more. These variables are subjective and certainly open to experimentation. As with all profiling variables, there are no fixed rules.
Pre-infusion pressure and duration should be viewed as being unrelated to extraction pressure and flow rate for the purpose of seeking optimum taste, but they do influence flow to varying degrees. In general, the finer the coffee, the more pre-infusion required to produce a specific flow rate, and the coarser the grind, the less pre-infusion required to produce the same flow rate. However, the pressure ramp-up speed can influence the upper extraction pressure.
Pressure ramp-up
Pressure ramp-up is the process of increasing pressure from pre-infusion to extraction pressure. The ramp-up variables are primarily the speed or rate of increase, and whether or not the ramp-up rate is even or variable. For example, the pressure increase rate can start slowly, and then increase as pressure rises, or inversely, a rapid start followed by a slowing rate as the upper pressure is approached. Regardless of the speed of ramp-up or whether or not the rate is constant or varied, the key is to maintain smoothness. Abrupt fluctuations can potentially disturb the puck causing the release of unwanted flavours.
The maximum obtainable pressure and flow rate can be influenced by a combination of pre-infusion variables and ramp-up speed. High pressures are easily obtained with fine grinds, but coarser grinds require careful manipulation to obtain both the required pre-infusion duration (to allow water sufficient time to penetrate the individual coffee grounds) and the desired flow rate. As a general rule, a coarser grind requires a faster pressure ramp-up in order to obtain full pressure.
It appears that a rapid increase forces the pre-infused coffee grounds more tightly together, which produces more resistance to flow. This increased resistance enables higher pressures to be obtained during extraction. The inverse also applies. Finely ground coffee can be extracted within the desired pressure range by using a slow pressure ramp-up. This seems to enable water to flow more easily through the puck (without channelling). Fine tuning this method requires experimentation with various combinations of pre-infusion variables. It should also be noted that limitations to the maximum and minimum grind sizes still apply, but this method enables a relatively broader range of sizes to be used.
Upper pressure
Conventional espresso extraction uses 9 bar of pressure. However, when pre-infusion is applied, it appears that pressures above 6 or 6.5 bar release unfavourable flavours. These flavours can be eliminated when higher pressures are used by shortening or skipping pre-infusion (similar parameters as conventional espresso extraction), but it is difficult or impossible to extract the subtle flavours or produce a rich and balanced shot to the same level without pre-infusion. It should be noted that different coffees will generally respond differently. As always, experimentation is the key.
The current theory to explain why it is necessary to use a lower than conventional extraction pressure when pre-infusion is applied is as follows: Pre-infusion enables water to penetrate into the individual coffee particles before commencement of extraction, therefore requiring less pressure to extract the soluble elements of the coffee. When no pre-infusion is used, the coffee particles remain dry until extraction. Therefore more pressure is required to penetrate water into the individual coffee particles far enough to extract the same amount of soluble elements.
Regardless of the accuracy of this theory, experimentation is the key. The effects of this variable can be tested easily without needing to alter other variables. Pressure is perhaps the most objective variable to measure, therefore enabling accurate and repeatable testing and experimentation.
Pressure ramp-down
Pressure ramp-down is the process of decreasing pressure from the upper pressure to the lower pressure. This step is not always required. For example, a fixed pressure profile requires no pressure change, and a profile that begins with a lower extraction pressure before increasing pressure requires no pressure ramp-down step.
The primary ramp-down variable is speed or rate of pressure decrease. Pressure can be decreased quite rapidly, or it can be a gradual reduction, and both methods produce quite different results. The ramp-down profile is a significant variable that should be viewed in conjunction with both the upper and lower extraction pressures and their durations. Similar to the ramp-up process, the key is smoothness without abrupt fluctuations.
Lower pressure
The lower pressure is a lower extraction pressure preceded by the pressure ramp-down and upper pressure. There are no specific rules, but results to date indicate that the lower pressure should not drop below 4 bar. Fixed pressure testing has shown that 4 bar is about the lowest pressure capable of a reasonable extraction, but different coffees will inevitably produce different results. As with the previous steps, experimentation is the key.
Putting it all together
Each of the above steps is equally important, and each can be varied relatively independent of each other. However, accumulation of all steps ultimately affects the resulting shot, and the number of potential variations is seemingly infinite. Therefore it is advisable to work on one step at a time in the overall profile, and take note of changes. As you become familiar with and confident in the changes of one step, move on to the next, and so on until you become a profiling master. Replicating the profiles shown below should save time and possibly many wasted shots until such time that your confidence and proficiency increases.
Where to from now
The current limitation of machines capable of manipulating variables to the degree as described in this article is a significant factor holding back people’s awareness of the potential that profiling offers. However, in light of the above discussion, it should be obvious that effective espresso extraction comprises significantly more potential variations than what conventional extraction theory suggests. The conventional extraction method is arguably the fastest way to produce specialty coffee, and considering the economics of running a busy cafe, making great coffee fast does make sense. However, if you want better than “great”, and seek the best possible coffee, it would be naive to ignore what profiling can and does offer.
It has also been suggested that current coffee roasting practices limit profiling potential. Coffee is currently roasted to suit machines using conventional extraction variables, but finding new roasting variables to compliment profiling could potentially reveal otherwise unknown characteristics of coffee that ultimately produce better espresso.
The final point or suggestion is to document and share your experiences. Copy the chart format shown below. Upload your profile onto coffee forums or anywhere that others can access, and describe your results. As noted in the introduction, the purpose of this article is to contribute to the pressure profiling knowledge-base by sharing experimentation data and results, as well as attempt to provide an objective standard that will enable others to replicate and compare results. It is hoped that this article achieves these objectives so we can learn from each other, and hopefully uncover the potential that profiling offers.
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Conventional Profile
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.
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Continuous Slow Profile
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.
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Short Stop Profile
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.
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Long Stop Profile
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.
