Pressure Profiling

Posted:  June 2nd, 2012 by:  wolfram comments:  4
pressure-profiling-teaser

Since the first big hype about pressure profiling one and a half years ago I couldn’t find any noteworthy information about it anymore. Why is that? Is it because pressure profiling hasn’t turned out to be the next big thing? Did people stop sharing their findings? In the past we were playing around with pressure profiling for a while and made our first findings. Nevertheless, I never did a more systematic “research” to underpin the findings so far nor could I find anything like this in the internet.

My intention for this post is to show, how pressure profiling can be incoporated into the barista toolkit. In no means will this be the definite guide to pressure profiling. As always, it is part of my own progress while strawling the world. As you will see in the following sections, pressure profiling isn’t for everybody. One need to be skilled to use it to an advance (it can also worsen things, if you don’t know how to handle it). Since I own a La Marzocco Strada EP myself and had the chance to play around with it broadly – pulling tons of shots, measuring them and comparing the results – I wanted to share my findings and hopefully get some reflections to it from the wider crowd.

One question that I hear a lot is, that pressure profiling might not be a big step and only be driven by manufacturers to have a new thing on the shelf. I can’t follow this argumentation. First, the development of pressure profiling was demanded from the user (barista) and taken seriously by different companies. Second, pressure profiling works, it adds another element to your toolkit, giving you more freedom on how you can work with a certain coffee. I don’t believe that development steps necessarily need to be big ones to deliver something that improves what we have at hand today. If you approach new topics from the scratch, the first steps are naturally bigger ones. Later-on improvements will be smaller and might not have such a great impact anymore, nevertheless numerous of those improvements still affect the game big time. One such improvement is the VST/La Marzocco filter basket, which turned out to have a significant impact on shot quality. Having different sized baskets allows for more freeedom of finding the proper dose for a certain coffee (instead of always been forced to fill the basket to the top) in addition the holes are more uniform in size and cover a larger area. I would consider this an important step, since you can taste the difference and can reproduce shots more easily.

So how is it with pressure profiling then?

Some people argue that pressure profiling isn’t necessary and that new machines already provide sufficient capabilities (pointing away from the Strada). There are several machines around, allowing for pressure adjustments throughout the shot.

  • The Slayer uses two pressure setpoints and you can switch back and forth between them. The pressure rises and falls accordingly but you are not able to set it to anything explicitly (holding the pressure at a point between the two setpoints wouldn’t work).
  • Some machines (like the new Nuova Simonelle Aurelia T3 or some of the Keys van der Westen machines) use pre-infusion profiles or slow pressure ramp-ups. While these build in profiles perfectly work for some coffees, they do not contribute to others.

As you can see later-on, there are several things you can do with pressure profiling, for which you need more flexibility in controlling the pressure. I favour the La Marzocco Strada EP, since I am able to produce any of those profiles as well as numerous more.

One thing has to be considered if talking about pressure profiling. There is a difference between pressure and flow rate. To be able to build up a certain pressure a specific resistance is required, hindering the water to flow. In the past one wouldn’t worry about this but what happend is this: you set the pressure at your pump to 9 bar, the pressure is controlled by a valve and held stable at the setpoint. You start extracting your shot, the pressure builds up against the resitance of the coffee in the portafilter. The extraction starts and washes out more and more of the coffee substances, thus reducing the resistance of the coffee. This automatically led to an increased flow of water since the pump still provides the 9 bar, but requiring a higher flow rate to do so. The longer the shot runs the more does this effect come into play until all substances are washed out (and no more can be taken) or the coffee swells. Nevertheless, in the past one wouldn’t consider this effect much. Today, if you are using a machine like the Strada, you are faced by the difference and have to take care of it yourself. Setting the lever (by which the pressure is controlled) to a certain setting will not hold the pressure stable, the pressure will actually lower, while the flow rate increases slightly. In the past you were already manipulating the flow rate by adapting the grind size and dose to get a certain extraction flow rate for the 9 bar pressure applied. But were the chosen grind size and dose the best choices when it comes to taste? Or did we just adapt it to make the process work?

So, how does espresso develop depending on the profile used?

Lets start simple. In the following you will see the difference of three profiles and how they affect the extraction rate of the coffee. For all profiles I use constants, except the pressure that is applied. I am using one of my coffees from backyard coffee, the Finca Santa Marta from Honduras, which is a natural, very fruity and sweet coffee. The dose for a double will always be 18 grams, having the same grind size, brewed at a temperature of 93°C to a total of 33 g of brewed espresso. What will change is the pressure (and flow rate) and thus the extraction time. The setup I use for testing can be found at the end of the post.

The following results do not take taste and aroma perception into account, it is just a technical evaluation of the extration ratio. If you are unfamiliar with the terms extraction ratio and brew strength have a look at my previous post.

Default Profile
  • pressure: 9 bar
  • extraction time: 26 seconds
  • extraction ratio: 20%
Low Profile
  • pressure: 3 bar
  • extraction time: 73 seconds
  • extraction ratio: 20,1%
High Profile
  • pressure: 12 bar
  • extraction time: 36 seconds
  • extraction ratio: 19,7%

I ran every extraction measurement three times to ensure that there is no failure due to preparation or measurement itself. The outcome varied slightly but stayed always in the range given above. For a defined amount of beverage the extraction ratios did not differ as much as I expected in the beginning. The taste and aroma of the shots were completely different, but we will get to this later. One thing you might have noticed already is the extration time. Brew at any length you like, as long as the flow rate is under control. Since I use pressure profiling I rarely end up having a shot finished at (say) 25 seconds.

How can we influence the espresso by applying pressure profiling?

If you ramp-up the pressure in the beginning of the shot very fast and to a high level of pressure (9+ bar) the coffee will be compressed, sealing it and reducing the flow rate rapidly. If instead you have a slow ramp-up time, are using a long low pressure pre-infusion or doing a low pressure extraction from the beginning the flow rate will usually be much higher. The sealing effect is related to the grind size and dose chosen. The finer the grind, the less the dose can be. If you go coarser you need a higher dose.

How can we incorporate this into the brewing process?

The flow rate and pressure can be used to control acidity and bitterness of the brew and the aroma spectrum accordingly. Thus playing around with pressure allows for finding the sweetspot for a certain coffee, without changing the grind size and/or dose or the temperature (if you are in the proper range of those parameters in general). If we do a full extraction on a single pressure level, a high pressure extraction brings out the bright notes of the coffee while a low pressure extraction brings out more of the darker notes. The flow rate will be similar in both cases, since the high pressure is caused by the higher resistance of the coffee bed (no water can pass through) while the lower pressure doesn’t push that much water through the coffee bed at all. The thing gets tricky, if we want to change the pressure throughout the shot, since the resistence of the coffee bed changes. Don’t expect that the extraction will behave the same at 6 bar, if you were switching to 3 bar for 10 seconds and are getting back to the 6 bar. The one decision you have to make at the beginning of the shot is how much do you want the coffee bed to be compressed. This dictates the flow rate that is required to reach a certain pressure level. Whatever you do in the first seconds of the shot cannot be fixed or made undone afterwards, thus you should know from the beginning what you want to achieve as an outcome and plan the pressure curve accordingly.

Now that we have a base knowledge about how the extraction behaves tecnically, we have to focus on the taste and aroma attributes of the brew. How does a certain profile affect the cup and how do I get to an espresso preparation setting that takes pressure profiling into account (in addition to the temeprature, dose, grind size and brew time)?

As I stated above, using pressure profiling allows for highliting brighter or darker notes in the coffee. The coffee aroma wheel separates aromas into three categories: enzymatic (flowery, fruity, herby), sugar browning (nutty, caramelly, chocolatty) and dry destillation (resinous, spicy, carbony). By using pressure profiling you can highlight either the enzymatic segment or the dry destillation segment. Aromas from the sugar browning segment seem to be present always in similar intensity levels. If you build up the pressure rapidly and to 9+ bar, you get a very slow extraction that is very bright and does contain way less dry destillation notes. If instead you are doing a slow ramp-up, a pre-infusion or low pressure extraction, you highlight more of the dry destillation aromas. Using this knowledge allows for new interpretations of your existing coffees, maybe lowering the temperature and balancing out the bright notes using pressure profiling highlights the coffee better, maybe the opposite is true. In addition the range of roast degrees in the lighter range are now acceessable to be used for espresso. I played around with certain light roasts, I would not have been able to use as espresso if brewed on my La Marzocco GB/5 at 9 bar, and got really great shots.

Another aspect of pressure profiling is the capability to use fresher coffee. I compared three different roasts of the Finca Santa Marta side-by-side. The first roast dated 18 days back, the second 10 days back and the third just 3 days. I usually prefer a rest of about 8 to 10 days for this coffee, if prepared “normal”, which would be my La Marzocco GB/5 at 9 bar. Why so? If prepared on the GB/5 the roast flavours were still pronounced if the resting time was less than five days. Starting at day seven the coffee turns out to be very clean and the aromas of this coffee are allowed to shine. The coffee starts to decrease slowly at about 18 days out of roast and gets totally boring at around six weeks after roasting. As mentioned above, by pressure profiling you can shift to a certain aroma spectrum. For the fresh roast I used a fast ramp-up to 11 bar for 12 seconds until the first drops of coffee appeared and reduced it to 7 bar till the end of the shot. The resulting espresso contained way less roast flavours. The characteristics of the coffee were a little different to what I was used to, but it was very good.

How to find the proper pressure profile?

I use a standard profile as a start and develop the profile from there. My standard profile is a 9 bar extraction, with a ramp-up time of three seconds to get to the 9 bar pressure. From there I develop the shot as usual:

  • finding the proper extraction time
  • finding the proper dose
  • finding the proper grind
  • finding the proper temperature

What I want to achieve is to find the sweetspot of the coffee as well as highlighting certain aromas. If I find something interesting in the coffee that I want to preserve, I stop changing the above parameters and start using pressure profiling.

Conclusion?

Pressure profiling isn’t for everybody. You need a brief understanding of the extraction process and its parameters. Even so, you will need some time to get familiar with the new flexibility. Untrained personel will be lost on a machine like the Strada. You need to know how the extraction process works and how to influence each parameter. Nevertheless, the Strada offers many new options and I really like working with it. If you are quality focused, you might also be able to incorporate it into a busy day. Profiles need to be changed, like you take care of the proper grind and dose.

The following equipment has been used throughout the testing:

  • La Marzocco Strada EP, 2 group
  • La Marzocco GB/5, 3 group
  • Mazzer Robur grinder
  • Two Kern scales
  • Small precision scale for drip tray
  • VST Refractometer II
  • FLUKE thermometer
  • SCACE device for an additional pressure and temperature control

Resources in the internet covering the topic:

4 Comments

Posted By: Anonymous On: August 26, 2012 At: 8:36 pm

[...] [...]

Posted By: Kenny B On: May 02, 2013 At: 11:29 am

Hi,

Thanks for the article, it’s a great read. We’ve recently bought a Strada EP, and have had fun working through profiles.

If you’d like to share thoughts anytime, feel free to drop us an email!

Kind Regards
K

Posted By: George Chow On: May 16, 2013 At: 7:27 am

Thanks for an informative article. I recently modified my 20 some years old Swiss made Harmellin espresso machine (modified previously with the addition of PID temperature control) with a Fluid-O-Tech pump (similar to the used in the La Marzocco Strada EP and found it to be very exciting! Now I can do things that was not possible before.
The question I have is if you have found the sweet spots (pressure wise) for the 4 stages of espresso I termed them as: pre-infusion phase, the bright phase, normal phase and the bitter phase. I am aware that I am talking in general terms and not specific to a particular coffee.
I went to the presentation by La Marzocco in San Francisco and the information I gathered was the curve is more or less a bar bell curve with the apex at around 9 bars. Since I do not have inline water, I have (in this case) the advantage of controlling the water pressure more precisely in the beginning and not be influenced by the city water line pressure. The fluid-O-Tech pump with brushless DC motor is excellent for this application since it can rotate at a slow speed without stalling.
I wonder if the sweet spot for pre-infusion phase is bringing the pressure up to 3 bars, hold it till liquid starts flowing and bring it up to x for the bright phase, hold it till the normal phase, bring it and hold it to y and hold it till the bitter phase and so on.
One way of approximately getting the switch points is by weight since I have no way of telling it by volume. So the question I have is what are the sweet spots pressures?
Since the motor is electronically controlled, I just have a potentiometer with a rotating knob to control the pressure and ramp rate.
Do you think it makes sense?
You response is greatly appreciated.
Sincerely
George

Posted By: wolfram On: July 21, 2013 At: 1:05 pm

Hi George, sorry for the late response, I am getting overrun by spam and your comment was somewhere in between.

The main thing you need to take care of is the flow rate. Pressure is just another tool you can use to control the flow rate. Since I am working on a Strado I changed how I use my “tools” to control the result. The “tools” are dosage, grind, temperature, pressure, brew duarion and contact time.

I usually use lower temperatures now, I usually use a corser grind level and I tend to have pretty long extractions. I rarely use a standard pressure setting, I change the profile depending on the coffee. The main goal ist to control the flow rate, which in turn results in the time given to the coffee to dissolve into the water.

Upon extraction start you have to decide, what you want to do with the shot. You won’t be able to fix stuff during the shot, if you started it wrong. If you did, start another shot from scratch.

At the beginning of the shot you can either force a higher flow rate, a lower flow rate or something in between. Higher flow rates are produced if you use a pre-infusion, a very slow pressure ramp-up or a low pressure extraction followed by ramping up to the desired extraction pressure. If you start the extraction using a very high pressure, the coffee bed gets compressed (way more than you can by tamping hard) and the flow is restricted.

Using a faster flow rate allows you to get higher in dose or grind finder (you are reducing the effect of higher dose or finer grind, since you are washing out the fines first, prior you get up to full pressure, this way the water can flow more easily through the coffee bed). In turn you can use a lower dose, if you are using pressure to make the coffee bed more dense and slow down the flow rate.

It really depends on the type and freshness of coffee you are using, which option you are choosing. I usually get higher in dose, coraser in grind and lower in temp, anything else is pressure profiling. The total extraction time (mine) is way of the chart, if you compare it to the “standards” defined in the acient times.

Hope this helpd. Get back to me anytime…

Wolfram

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