Continued thoughts on pressure profiling

I wrote a couple of months ago about pressure profiling.  It remains a little divisive in the industry, with strongly polarised thoughts on its use and importance.  Recently I’ve been thinking more and more about it, what I think is happening to the coffee, why lever machines produce the espresso they do and what the possibilities are for modern machines that can produce a range of pressures during the shot.

I warn you now that things might get a little nerdy.  I will also do my best to distinguish between what is theory, what is opinion and what I think we can tentatively accept as fact.  I’m also going to make some assertions about modern espresso brewing and the problems therein.  I should also add that this is the longest post I’ve ever written, and covers a lot of ground…

The Modern Espresso Recipe

This may be stating the obvious but I think it is important to go over again before we get into pressure profiling.  For a long time espresso machines were built to extract coffee using a fairly high water to coffee ratio (high by today’s standards).  7g of coffee per shot was used and the resulting brew weighed (and often still weighs) around two to three times that of the coffee.  Because the coffee was rarely as freshly roasted or freshly ground as today that shot was around the 25-30ml mark when prepared into a shot glass.

Modern doses, for most quality focused shops, are much higher – usually around the 20g mark 1.  This likely started because people were grinding to order and dosing using the basket as a volumetric measurement.  Most double baskets hold (without excess settling or compression) that much coffee when filled evenly and swept flat with a finger or dosing tool.

Along with the increased dose came an increasing preference amongst baristas for more concentrated/stronger shots.  I know we don’t like the word strong but it is the right word.  The ratio of dissolved coffee solids to water in the cup was much higher than ever before.  Baristas were using freshly roasted coffee with a lot more CO2 present so their stronger shots had the appearance of greater volume.  When freshly brewed, despite using significantly less water, they often looked around 25ml.  These shots often weighed as much as the coffee used (instead of twice that) so a double espresso from 20g of coffee would often weigh no more than 20g.

So far, so obvious (I think) – but it is worth taking a step back and looking at modern espresso.  We are using the same machines to brew 40-50% more ground coffee with 50-70% less water.  As a result most brewed and served like this is going to be under extracted.  It will be dense, thick, creamy espresso – but it could be so much better.  Some argue that shots like these have an unpleasant acidity that we’ve gotten used to, the way that people who deal with very dark roasted coffee might become accustomed to high levels of bitterness.

In my opinion I think we’ve adjusted the way we roast for espresso to accomodate this.  We roast a little darker, we roast a little longer.  When we cup our espresso roasts we notice that we’ve introduced roast flavours we don’t want – but when we brew them as slightly underextracted espresso they fall into the background.  Acidity is brought up in the shot, despite being muted by roast, and we get something pretty tasty.  I’m not saying we’re all serving bad espresso – I am saying that there is a clear opportunity to serve better espresso.

This also explains the double hump phenomenon – roasting darker than we should, but underextracting slightly can produce a pretty good espresso with a relatively low extraction.  As we creep up from 16% to 18% we start to pick up some of the unpleasant accidental byproducts of our roasts, until that too becomes balanced as the shots fall into 19% to 20% range.  I can completely understand someone’s preference for relatively underextracted shots (as many have noted), but I think overall the shots can be improved with increased extraction.  I am aware this theory probably won’t make me very popular.  I’m not saying people are roasting incorrectly, and I believe we’ve gotten here based on taste.  Maybe I’m completely wrong on this – but it will be interesting to explore some more.

Roasting darker also helps us extract the coffee more easily, as lighter roasts are usually very difficult to extract due to their density.  We wrote off these light roasts as being bad for espresso because they lacked balance – much as we wrote off dense, high grown coffees for a long time.   Too much acidity, not enough sweetness.  However – this is the same description I’d give to any underextracted espresso…

The only way I’ve found to extract lighter roasts in a way that is balanced is to increase the amount of brew water used – essentially to pull a longer shot.  By using more brew water I am able to drag enough of the tasty solubles into the cup – the downside to this is the loss of body, texture and intensity that sets espresso apart as a brew method.

I’ll come back to all of this once I’ve gone back to pressure profiling, starting with a few observations and some thoughts on lever espresso machines.

Why Lever Espresso Machines Work So Well

There is no denying that lever machines are capable of producing some delicious and distinctive espresso.  The pressure profile of a lever has two distinguishing features:

- A period at the beginning of the extraction with low brew pressure (below 3 bars)

- A period of the extraction with a declining brew pressure as the spring expands up until the end of the brew

Interestingly a number of the people I spoke to who have pressure profilers have ended up in a similar place.  While the exact nature of the profiles varied these two things tended to be in common.  Perhaps these people were left as muddled by the infinite possibilities (like I was) and just reverted back to a “known” profile and interpreted it in their own way.  Perhaps they were all just onto something.  I want to look at each of these two points, and discuss them a little more.

Preinfusion

Preinfusion is the term we tend to use for a period of extraction where water is soaking into dry coffee without really passing through under pressure.  This is done in many machines using flow restrictors or with preinfusion chambers.  I consider the following statement to be pretty accurate:

The flow of brew water through the cake will be faster if there has been preinfusion, compared to immediately brewing under high pressure.

If you have a flow restricted machine next to an otherwise identical unrestricted machine and you dial in for the flow restricted machine you’ll find that same dose and grind will choke the unrestricted machine.  The prevailing theory (which I think is probably right) is to do with fines migration.  Immediate high pressure pushes many of the finer particles to the bottom of the puck where they create a little sandbag of resistance.  Unrestricted machines will often exhibit a slow down in flow rate towards the end of the shot as the fines continue to accumulate.  The hypothesis with preinfusion is that the cake swells with water, trapping the fines in place before the pressure hits.  This prevents the same level of accumulation.

What is interesting is that the longer your preinfusion (to a point) – the faster the resulting flow rate.  To give you an idea of preinfusion times on lever machines I’ll borrow Gwilym’s technique of an 8 second preinfusion.  The rule of thumb is that you want to completely soak the cake before the brew.  This is going to be a function of your dose (the depth of the puck) and the preinfusion pressure.  20g at 2 bars takes around 8 seconds.

This means that you can grind your coffee finer, for the same dose, when using preinfusion.  This, I think, is excellent news if you are brewing a modern recipe where you need to extract a lot of coffee without using too much water.

The Ramp Down

The reduction in pressure in the middle to end of the espresso is an interesting one that is still causing me some problems.  I really ought to use diagrams to explain this better.  The following diagram is not accurate – merely a mixture of an approximation of what is happening, mixed with a bit of a guess.

The diagram shows extraction on the vertical.  I’ve highlighted the range between 18% and 21% where I think good extraction lies.  The horizontal axis is brew time.  The blue line represents a good 9 bars extraction (though not accurately – I know Vince Fedele has done accurate work on this!).  Obviously extraction is much faster at the start of the shot (we know that from the colour of the first part of the espresso alone).  As we extract the resulting extract is getting weaker (growing paler) and our rate of extraction decreases.  In most good espressos the window of tasty is between 25 and 30 seconds – correlating to the range of tasty extraction on the diagram.

With decreased pressure comes a decreased flow rate.  My first thought on why this might be good is illustrated on the diagram.  As the pressure decreases the rate of liquid hitting the cup slows, so therefore the rate of extraction would decrease.  Perhaps this would extend the window of tastiness wider?  Perhaps this would make it easier to serve better shots?

This may be the case but something else popped into my head.  The liquid flowing through the coffee puck would be moving slower and therefore be carrying more solvents with it.  This would mean that if we look at mass in the cup, and not time, then we’d see a different diagram.  Again extraction % is on the vertical, but on the horizontal there is the mass in grams of a single espresso.  Also again – this is not accurate, merely a visual aid!

This diagram is a little confusing, because it is weird to think about espresso brewing and not be thinking about time.  Imagine you’re watching the scale you put under your spouts (because doing that – evenly occasionally - is a good thing.)  With a ramp down the extraction is increasing at a faster rate per gram of espresso, compared to a straight 9 bars shot.

For an accurate chart showing TDS, Extraction and espresso mass I am grateful to Vince Fedele.  This chart represents what should be a pretty tasty espresso – brewed under standard pressure conditions.

So far the above idea is based on my own empirical observations, and my increasing need to better understand the effect of flow rate through coffee.

Back to the Lever Machine

So – does the theory match my own observations of shots from lever machines?  Yes.  I noticed, though didn’t give much thought to it at the time, that the shots that Gwilym would pull me on his lever were surprisingly strong and balanced.  (Charting above 13% strength and being tasty is surprisingly rare!)

The theory would be that lever profiles produce better extraction when using a large amount of coffee and a small amount of brew water – exactly what most quality focused shops around the world are trying to do!

So should we all be using lever machines?  Should all pressure profiling machines be dialled into to exactly replicate that curve?  I don’t think so – unless you want a good solution immediately with a minimum of work.  The lever profile is something of an accident resulting from the initial design of the machines.  You have to have a period of preinfusion because you need to fill the chamber above the coffee with brew water.  The expansion of spring probably wasn’t considered to be interesting or important early on.  It was just a way of exerting more pressure than steam, line pressure or air had been able to achieve in previous machine designs.  Put simply – a spring wasn’t built into the design because a decline in pressure was considered important.  It was more an economic way to achieve very high pressures in a simple, mechanical way. I think there is a great need to better understand the soak/preinfusion phase as well as the ramp down phase too.

It would have probably seemed quite defeatist if I’d opened this post with the idea that the main benefit of pressure profiling would be that we could pull dense, strong but balanced shots of espresso.  It seems so anti climactic, especially when pressure profiling offers such possibilities to explore.  When you can do anything the idea quickly emerges that hidden somewhere out there – amongst infinite squiggly curves and shapes of profiles – there is something totally new, something that will blow our minds.  I’m not so sure, and I’m actually pretty excited about the increased extraction idea for another reason:

Introducing denser, difficult to extract, coffees to this kind of profile means that we might find it easier to achieve an excellent extraction of light roasted coffees.  Extracting them more efficiently we may well get great balance, and all the strength and mouthfeel of great espresso – with the benefit of an even cleaner finish.  We might be able to roast all our coffees for espresso a touch lighter, keep a little more complexity in the coffee, bring out even more sweetness from our shots.  That is pretty exciting to me.

Where do we go from here?

I remember writing in that last post on profiling that it would be good to get a little cohesive, collaborative work on this front.  I’m going to propose a couple of experiments that I think would be immensely useful because we’d start to understand how we are influencing our espresso brewing.  I certainly think some good results can be obtained from focusing on those two elements of the brew.  However, I’d rather open the floor up to some feedback.  I think I’ve written enough for now!

  1. I’ll be honest and admit my cynicism about dose.  Most people who say they use 18g are using 20g and most who say 20g are using 22g+  ↩︎

50 Comments

  1. I need to read this another 3 times or so before I can really comprehend all of it.

  2. As a lever machine owner I’ve been rolling some of these points around my head for a couple of months, without really being clear as to any conclusions. Many thanks James for setting this all out far more clearly than I have been able to think about it.
    One related, but slightly off topic question – If people are using different pressure profiles to bring out different characteristics of different coffees (such as Notes, Music & Coffee), should / could you be selecting and roasting coffee according to the machine / pressure profile in use? Or, more simply – What coffees and roasts work best with a traditional lever machine?

  3. Really nice, interesting post James. I feel like there is so much more to learn about extracting espresso.

    The industry is constantly exploring this process in a non-systematic way..
    We develop some insight into one area, then another, but between experimentation, and shop-floor observation, the list of variables and differences are too great. When I first heard about it, I had partly hopped the GCQRI would be involved in this, however it they are addressing other (very important) necessary issues in the industry, which is awesome.

    Is there scope by anyone in the industry (willing to share the information) to undertake thorough, systematic and comprehensive research? Where, under controlled conditions all components of the extraction process could be considered independently, and in conjunction with other variables… That would be such a good starting point..

  4. I’m getting excited about pressure profiling for a slightly different and unusual reason. Where I’m from (Ottawa, Canada), we have a lot of older lead pipes, but moreover, we have nice low TDS (90 – 100 ppm), but also a more alkaline pH (readings between 8-8.4 at times!). This presents for us a strange situation that not a lot of people in coffee I (or Ian C. my colleague) think are concerned with.

    To deal with the low tds and high pH, the total alkalinity really dips. This is good on one hand because things like lead and such don’t leach into the water system… but on the other hand it means that it’s difficult to extract anything at all into our water. So this means we are constantly brewing our espresso in the window of 203-205f to compensate for the under extraction that results from our water chemistry.

    The thought that we could use pressure to our advantage will mean we will be able to hopefully brew at lower temperatures (possibly) and achieve more balance and more complexity (and maybe some sweetness!).

    We are excited to explore all this.

    Merci,
    Laura perry

  5. This is one of your most thoughtful and well-written/conceived posts yet, Jim. It makes complete sense to me, and it also explains much of my own personal experience of the past 10 years with a home lever machine (no springs).

    I’ve found myself through trial-and-error developing a system of pre-infusion, whereby I try to maximize the resistance of the water to the lever pull in the group head. Just before it reaches a saturation point where I begin to see some extraction finally run through the grounds. At which point I begin a steady pull and have used the pressure feedback of the lever arm to guide shots pretty much precisely as you’ve mapped out above.

    Is better espresso extraction possible? Most certainly. But it does explain how I have sort of “organically” evolved my lever pull habits to model what you’ve written here, almost exactly as you’ve described.

    I had not considered that I have been doing pre-infusion and a deliberate ramp-down pressure extraction for years, but this points a finger that I have been doing precisely just that.

  6. I don’t think there is a relationship between a coffee/roast and a machine. I think a change in profile may allow improvements in extraction for certain difficult coffees. I think it will allow different presentations (mostly in terms of strength) of a coffee as well.

  7. Outside of the experiments of people like Illy, I don’t think anyone is doing much in the way of systematic and controlled research. I think the industry has a mindset wherein a simple experiment will someone explain a complex and nuanced process, and the idea of chipping away at research seems pretty boring/lacking innovation.

    I think that is slowly starting to change, but the problem is that very few people capable of physically running the tests necessary to understand extraction of great coffee have the scientific training and background that could result in this sort of thing actually being published.

    Maybe you and I should collaborate on a paper….

  8. I recall reading something a few years back from Instaurator on this very topic James, he had some great scace graphs etc based on various machines and methods and the resulting brews (taste), if you havnt talked to him already and got ahold of his information I suggest you get ahold of it, I recall him profiling based on roast and bean denisty also, some of the information will of course be reduntant now but certainly still thought provoking.
    Great post by the way, very enlightening.

  9. Thankyoufor agreat post,! Our Strada still hasn’t arrived, but will be playing with longer pre infusion relative to dose tomorrow on linea paddle, can’t wait, I too am very excited to develop espresso with less compromise, sweet complex and clean!

  10. Genuinely inspired post, James. You have an ability to cut through all the bollocks* that we – the young and often faddish specialty coffee industry – sometimes espouse! It makes for thought-provoking reading.

    *= I’m talking about those unexamined assumptions we all make… for example: 1) customers or wholesale clients who think anything pulled before 2nd crack tastes “weak” and won’t listen to any other opinion; 2) the trend of cafes switching to triple baskets (25g+) without questioning their “more is better” mindset; 3) I wish that I enjoyed light roasts as espresso, but I don’t! So do I wish that because that’s what’s “in” at the moment? Or do I dislike light roasts through espresso because I’ve simply become accustomed to roasty flavours?

    Thanks for the thoughts.
    Cheers
    Stuart.

  11. As always, great post James. Backs up quite a bit of what we’ve been experiencing at Caffe Streets in Chicago with pressure profiling. I am curious about the comment concerning higher soluble concentration due to the increased dwell time on ramping down. This would account for the large body found in ramped down shots but I have also experienced serious diminishment of bitterness, would this have to do with the decrease of agitation? I’m not very clear about the effects of agitation vs dwell time on flavor in the final espresso, something I need to look into.

  12. Thanks for posting this, James. I just have time for some brief comments:

    1. Great point about how some may have unwittingly adapted their typical roasting methods to suit the current ultra-ristretto espresso style.

    2. I’ve repeatedly measured the difference in extraction yield between preinfused and standard shots on a Speedster espresso machine. As you stated, the preinfused shots must be ground a little finer to keep the flow rate constant. The difference in yield is quite small — preinfusion usually gives about a 0.5% increase. I don’t think this is very significant, tastewise. Of course, the Speedster’s “standard” shot already has some preinfusion built in. Perhaps there would be more than 0.5% difference between a thoroughly preinfused shot and one that got slammed with 9 bars within a second or two.

    3. Your graph of Extraction vs Mass expresses the HOPE that many of us have for the value of pressure profiling. But do you have data that brings this out of the realm of speculation? It’s not clear to me if you have actually tested this. The extraction-enhancing effect you propose may be real, but again, it may not be significant enough to be a game-changer.

    4. Everyone seems to talk about the declining pressure profile. But if the aim is to extract more solids by increasing contact time, why not do so by simply extracting at 5 or 6 bar? Then you wouldn’t need the fancy profiling gear; instead, just readjust the pump. Would this have too much of an adverse effect on texture? I haven’t tried it.

    5. One thing that is rarely mentioned is the sanctity of the 23-30 second shot time “rule.” With brewed coffee, we seem to get good results with a very wide range of brew times. It is only recently in espresso, with the growing popularity of extended preinfusion and pressure profiling, that the 25 second rule may be forever revised.

  13. RE/ point 4: While playing around with various brew pressures we had this thought too. Upon exploring it further we found that coffee’s brewed at 6 bars had a lot of the positive aspects of a well profilled shot. They all, however, tasted like they were ‘missing something’. It was hard to quantify but the taste never quite felt right.
    After a few weeks of this brewing like this, vs 6second ramps up to 9bars and long ramps down to 4bars we hypothesized that 9bars was needed to get everything out of the bean, but wasn’t necesarilly the best point to do the majority of brewing from.
    We theorize that pre-infusion, followed by a majority brew at somewhere between 6 and 8 bars, with a breif stopover (say between two and four seconds) at 9 bars and a final long ramp back down to four would work best with our coffee.
    We’re waiting on a next gen synesso to arrive before we can actually test this theory.

  14. Thanks for comments Andy!

    To respond:

    1 – I expected a little discussion on this one/a little abuse. Perhaps that will happen more privately… I don’t think it is a bad thing to hope we can all roast a little lighter…

    2 – I’ve seen some quite dramatic changes in flow rate with changing preinfusion – though I am sure there is a point where no increase is seen. Should be a fairly simple experiment to run. I’d noticed a similar bump of around .5%, though this could also be due to an increased overall contact time.

    3 – Sorry for not making this clear. I have not done the necessary experiments on this yet. I plan to though!

    4 – I don’t know if low pressure shots would extract more with the same dose of water. I’ve certainly had experiences similar to Ian’s where brewing at 6 bars resulted in a surprising lack of body and complexity.

    5 – I think this could remain a rule of pressured contact time, and have preinfusion as a separate portion – much like lever machines where the preinfusion time is around 6-10s and the brew time still around 25-30 (post spring release).

  15. Nice, interesting post James.
    I worry a little about the trend of using larger doses of coffee than the 6-7g shot we were using in the past, the strength and acidity of espresso coffees I often come across are a little too much for me.
    I agree that our espresso coffees are certainly stronger these days, often as a result of poor cup choice/water & milk ratio in our milky coffee world perhaps?
    I agree entirely that most Bariste are unknowingly using more coffee than they think, as you say, they simply fill the filter – why don’t people experiment more with smaller filters? after all they come in a range of sizes!
    I must admit that for those people who are looking at getting the very best espresso, I would certainly look at trying different blends to suit their machine and importantly their water? The designs are now so varied (I am lucky, I get to experiment with many types of machine at work) that I think this is essential.
    I love the the fact that we are taking another look at lever machines, they often produce better espresso that the design would suggest is possible – they too are often more varied in design than expected. I have a fabulous 1950′s Faema in for a service currently that employes a long coiled water pipe to adjust temperature for instance.
    The pre-infusion/group design question seems to grow and grow with many manufacturers now offering a stable, adjustable temperature group design.
    More machines with seperate boilers too, one with hot water and steam, one with water for the groups. This sounds like a great idea but often lets you down – the small diameter tube-like design of the boiler supplying the groups for instance is often subject to odd temperature fluctuations…
    I visited several manufacturers in Italy in spring 2010 and it’s obvious that this is a big talking point currently. The new Rancilio Classe 10 for instance is a high tech answer to stability issues, sensors monitor the machine and quickly react to use and changes in profile.
    With regard to pre-infusion, we have two machines here for services at the moment that have it. Interestingly, they both have the well known and respected Faema designed E61 group.
    One machine has electronic pre-infusion – water is pumped into the group/filter for a couple of seconds and then hesitates before “starting again”, the other has mechanical pre-infusion whereby the initial pressure and surge of water are absorbed by a spring loaded piston that allows a chamber at the rear of the group to fill before extraction begins. Both effective but in quite different ways and provide subtle differences to flavour.
    I think we should look again at water too, our area is served by different water companies/water and it does make a difference. Tea shows it up very well – amber and clear one minute and half a mile away it can be muddy brown with a film on top!
    Keep up the good work…
    Tony Ellis

  16. Having used a Strada, many lever machines, and many different pump driven machines the following question remains unanswered for me.

    Pressure profiling is interesting but i something no one ever seems to mention is the difference in manner in which the pressure going to the espresso is created and what impact this may have? The pump espresso machine uses a rotary vane pump and in doing so the pressure it creates has a high frequency pulse, to what extent this is dampened by the internals of different espresso machines and what effect this has i do not know. Lever machines use a piston and deliver pressure in a constant and but decreasing rate. This has always created a feeling for me that the main weakness of the pump driven espresso machine is its “soda pump.”

    On an unrelated note. I have always mechanical solutions to problems to be somewhat more fascinating and elegant. The espresso lever fits into this category perfectly. It is a beautiful solution for creating espresso and was created and perfected before people were measuring the dissolved solids in espresso shots. I think about this and marvel at the ingenuity of the men who created it.

    Also a final word of advice to those looking to purchase a Strada. Get the EP.

  17. hello james
    i built the pressure profile these day, i tried a couple of combination pressure profile, still finding a good profile.
    if anyone have a pressure profile to test, post it here and let me try, i will write a result here. or if you live in hong kong, we can test and share.

  18. hello james
    i built the pressure profile these day, i tried a couple of combination pressure profile, still finding a good profile.
    if anyone have a pressure profile to test, post it here and let me try, i will write a result here. or if you live in hong kong, we can test and share.

  19. It’s true that typical rotary pumps produce a pulsating output (~115 pulses per second in 60 Hz countries and ~96 pulses per second in 50 hz countries). But lever machines do not produce a pulse-free output, either. The piston seal does not slide with perfectly smooth action down the side of the cylinder. Instead, on a micro level, it alternately grabs and releases, grabs and releases. This phenomenon is called “stiction,” and its magnitude depends on many factors including the age, materials and cleanliness of the seal and cylinder wall.

    Given this situation, it is possible that the properties of lever shots vs pump shots have less to due with the way the pressure is generated and more to due with the numerous other differences in the way the brew water is presented to the coffee cake.

  20. Re: your observation (and Ian’s) that 6 bar shots may lack body and complexity:

    6 bars may not emulsify oils well enough (think poorly made, runny mayonnaise vs the highly textured good stuff). Also, 9 bars may force more fines through the basket perforations, increasing body.

    As far as flavor is concerned, many people notice that shots pulled at 11 or 12 bars taste rather bitter. Perhaps 9 bars extracts enough bitter flavors to add interesting complexity, but 6 bars ain’t enough to do the trick.

    Total speculation here, I have no data whatsoever to prove these ramblings….

  21. just tried, 4 sec in 2 bar, 6 sec in 4 bar, 6 sec ramp up from 4 bar to 9 bar, then ramp down to 6 bar, ok but no excellent.
    i tried 22 sec per-infusion, than ramp up, ramp down, no bitter taste, char. so good but no much body.

  22. just tried 7 shots, the result is, how to let the water to get deep inside the coffee cake, tried 2 bar 5 seconds pre-infusion, and 5 bar 5 seconds pre-infusion, 4bar….. 6 bar……. etc…….
    5 bar 5 seconds let the water to get inside the cake then 2 bar 6 seconds to let the cake extent the surface, final, 9 bar to force it, then ramp down.
    i think i will buy a flow meter later.

  23. tried a few shots, the result is, the flow rate is very important, maybe schomer is right, if using a motor > 350w single phase, flow rate is 38L/h, and a perfect grinder….. ha ha ha forget it.
    jim is right too, the sandbag….. it appears when the flow rate slow.

  24. My 2 cents.

    Some research, a little (OK, a lot) of attentiveness, and the patience to methodically trial/dial in the espresso does go a long way. Almost any decent coffee, on any decent machine, can make a beautiful, balanced and delightful coffee in caring hands. We’re not framing these things, after all! Often undue focus is placed on the equipment, at the expense of knowledge training and practice. Boys will be boys!

    Often, I use an analogy: I am pretty sure Tiger could play an excellent round of golf using my crappy clubs.

    So, maybe don’t be so hasty to assume that the latest technological upgrade will necessarily improve your game. First, you have to know the coffee, the process, and the equipment. Yesterday, we were pulling shots on a machine *without* temperature adjustment, pre-infusion or pressure profiling. I could simply not insist to the cafe that must immediately go and replace their equipment. Did we succeed in making really nice, drinkable, focused, balanced espresso? Yes, eventually. When the tools are in your hands, you have to learn to use them.

    Crap, that sounded lectur-y. Need to work on my skill in using this tool (language).

    Kudos on bringing out a good point.

  25. good article by Mr James but OMG how interesting is this water situation Laura has, very interesting.

    I think you would need to do research cross manufacturers, people can disregard research if its laden with self interest or opinion. Ever forward

  26. “We roast a little darker, we roast a little longer. When we cup our espresso roasts we notice that we’ve introduced roast flavours we don’t want”

    Are roast flavours undesirable??

  27. James yet another great topic,looking forward not only will scales in the drip trays be required, but the espresso machine designers will have to provide programmable pressure curves that a barista can save and use for a particular blend if and when required.Or do you think it would be necessary to profile every shot as per the paddle system on the La Marzzocos

  28. Just ran a quick experiment to see how extraction yield and shot time vary as one changes the pump pressure. Grind setting was not changed. Dose and shot mass were kept as constant as possible. Pressure measurements were made at the portafilter with a Scarce device. Here is the data,* rounded off for clarity, but still very close to the actual numbers:

    8 bar, 24 seconds, 19.0% solubles yield
    6 bar, 26 seconds, 19.5% solubles yield
    5 bar, 28 seconds, 20.0% solubles yield

    These are non-profiled shots with a flat pressure curve (after preinfusion, of course). Due to time constraints and overall laziness, I did only one shot at each pressure, so this is not “proof” by any means; it’s just suggestive of a possible trend.

    Honestly, I’m kind of shocked that the result was so dramatic. I wouldn’t have expected that much of a difference. Also, perhaps simply fining up the grind to make the second and third shots flow slightly slower might have increased the yield to this extent. In my experience, grind changes aren’t as effective as these pressure changes appear to have been, but I could be mistaken.

    My favorite was the 6 bar shot — sweeter, not as bitter, although yeah, the body was a little thinner.

    * Or, as they say in the UK, here “are” the data.

  29. Wow, that’s some intersting results, thanks for posting that Andy. It would be interesting to if there was any difference or correlation between brewing at 6 bars for half the time and then 9 bars (or 8 etc) for the remainder, vs brewing 9bars for the first half of the shot and 6 in the finish.
    I suspect that the variables are not entirely independent.

  30. Independent variables, that’s an interesting topic.

    Unlike espresso, Aeropress coffee is famous for enabling baristas to easily and independently manipulate almost all the variables: dose, grind, agitation, contact time, brew volume, temperature, etc.

    Espresso is different. It is difficult or impossible to isolate the effect of just one variable. For instance, shot time (contact time) is affected by almost everything else: dose, grind, preinfusion, pressure, coffee type, basket type, etc…if you change the pressure and want to keep shot time constant, you have to change something else, too. Even a new tattoo has been known to change the flavor of the espresso.

    I guess that’s why espresso is so interesting. ;-)

  31. I’m not sure of its effects and i know on a dual boiler machine like a La Mar or a Synesso would have a dampening effect. I just find it interesting that it does not seemed to be mention very much. I agree that the main difference between pistons and conventional pump machines is the decrease in pressure at the end of a shot.

    Thanks for your reply it was informative and interesting.

  32. Its funny hearing Schomer’s name and thinking how at the time we were looking for set variables. 9bar 200f 24-28 seconds…bla….bla..bla. Pressure profiling is here now. Temperature curves are the future!

  33. Someone asked who should be doing this kind of research…You and Me is the appropriate answer.

    One of the reasons for growth in Specialty Coffee is that we are putting these thoughts into actions and we are experimenting. It is the job of the following generation to disprove all the rules laid down by the former! Or am I being Naive? Has it been happening but not spoken of?

    The reason we’re successful as a movement (too grand a word, perhaps) is that we’re doing what the big roasters should have been doing decades ago. There must be someone other than Illy that has looked into this kind of thing in detail, surely…But maybe not.

    Great blog, Mr. Hoffman. Please continue with the critical analyses.

  34. Pressure profiling is a misnomer with due respect to the pioneers – Ermacoff, Scace, & Schecter. It should be renamed as flowrate profiling because, after all, that is what “we” are attempting to control.

    And, I said it before on HB, but I’ll say it again – get the same out of 18g as you do with 20g and a shop owner will be happy – $$$.

  35. This is one of the best coffee pieces I have ever read – bravo. Well thought out, well researched and huge breath of fresh air. Seriously, I am moved. Todd Carmichael

  36. Insightful piece, Mr. Hoffmann. I have over 11 years experience with chromatography (in biotech), and I am finally cutting the umbilical cord to take the leap into a life of specialty coffee. Compared to you (and to all of the coffee experts on this post), I’m a newbie to espresso. While the discussions that surround manipulation of (inlet) pressure, time, dose, etc. seem significant…have you given any thought to back-pressure? The coffee puck is much like a resin bed in a chromatography column used to purify proteins in a laboratory. In addition to manipulation of inlet pressure (at the top of the resin bed, or in this case, the puck), I would also vary back-pressure in order to increase/decrease residence time of the solution as it moves through the column. In other words, with all other variables remaining static, one could consider applying back-pressure to the coffee puck and increase contact time. This could theoretically aid in extraction, especially with a lighter roast, yes?

    I realize that (at least to my knowledge) there are no existing espresso machines that allow the barista to apply back-pressure, but I’m hoping that my comment may catalyze a bit of thought on the possibility.

    Thank you for your thoughts!

  37. If you cup (as in the Cupping method, not as espresso)  a coffee liberated at 2nd crack, and the same coffee liberated 30 seconds before, and compare the flavours, the answer seems clear. Perhaps I’m oversimplifying! It comes down to personal preference of flavours no doubt. Most ‘coffee people’ I know do not find smoke, toast, char, tobacco, etc, desirable; but this is hardly an average opinion of the general coffee-drinking public in my country.

  38. If you cup (as in the Cupping method, not as espresso)  a coffee liberated at 2nd crack, and the same coffee liberated 30 seconds before, and compare the flavours, the answer seems clear. Perhaps I’m oversimplifying! It comes down to personal preference of flavours no doubt. Most ‘coffee people’ I know do not find smoke, toast, char, tobacco, etc, desirable; but this is hardly an average opinion of the general coffee-drinking public in my country.

Submit a comment