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January 30, 2017 /
Distribution Test Results

Testing distribution methods for espresso is turning out be quite a journey. This post is another step toward understanding what’s actually going on between the grinder and espresso machine.

If you’re new here: three weeks ago I sent out a survey about distribution methods. The results and discussion are here. This week I’ve set out the post as a pseudo-scientific paper. It’s not strictly formatted or written as such, because I wanted it to be easily read and understood by everyone. That said, I think it’s important to at least loosely structure my experimental posts this way.

Abstract

The test I ran this week might seem a bit weird at first, but I’m certain that it is an elegant and meaningful metric. Essentially, the test measures a method’s ability to distribute a consistent mass of coffee into a fixed volume of the basket.

Introduction

As I mentioned in that previous post, distribution methods should be evaluated by their quality of extraction, consistency, speed and cleanliness. It would be pretty difficult and time consuming to test all of these things in one fell swoop. So I’ve chosen to break it down, and run a series of tests that will (hopefully!) help us understand what’s going on from different perspectives. At its most fundamental level, a distribution method is trying to evenly arrange the coffee grinds in the basket. It should result in a consistent density of grinds from side to side and top to bottom. Working towards a “maximum limit” like this is great for testing because there’s no such thing as “too even”. Once we understand this, then it becomes much easier to design a test that evaluates evenness.

Materials And Methods

The test I designed is quite simple, and doesn’t even involve brewing the coffee. It is purely a test of a method’s consistency and the evenness of grinds within the basket. Here’s how it went down: I chose three methods that represent the overarching schools of thought in espresso distribution. I did this because many methods are actually quite similar, and I needed to save time! 1) Just tamp it. – Grind directly into the basket, aiming to distribute the grinds as evenly as possible. – Tap vertically on the grinder forks twice. – Tamp. 2) Manipulate the top layer of grinds with your hand/palm/tool. (For this I chose the Stockfleth method as I’m most comfortable with it.) – Grind directly into the basket, aiming to distribute the grinds as evenly as possible. – Tap vertically on the grinder forks twice. – Move the grinds around with ones finger until the top surface is perfectly smooth and even. – Tamp 3) Tap vertically and horizontally. – Grind directly into the basket, aiming to distribute the grinds as evenly as possible. – Tap vertically on the grinder forks twice. – Tap the side of the portafilter with one’s palm until the grinds are perfectly levelled. – Tamp For each distribution method, I used a little bit too much coffee (0.5-1g above my target of 20.8g) and distributed it in the basket as required. I then tamped very firmly until the grinds stopped compressing. I used much more pressure than I normally would on the bar, because I wanted to remove tamp-related density of grinds as a variable. Here’s a quick chart explaining why.

Tamping Pressure

As you can see, small changes in pressure make a massive difference to the density of the grounds when you’re tamping. This effect is lessened with a medium or ‘standard’ tamp pressure and is almost negligible when tamping very hard. At a certain point, no matter how hard you tamp, the density won’t change at all. This is why I chose to tamp so hard – so it could be eliminated as a variable affecting the density of the grounds. Here’s where things get a bit weird, so stay with me. I wanted to measure the how well a method can distribute grinds within the basket. To do this, I needed to isolate a very consistent volume of the basket and weigh it. The consistency of coffee mass within that volume of space should be an indicator of how evenly the coffee is distributed. As I mentioned above, I distributed and tamped 0.5-1g extra coffee in each handle. This left me with some excess grinds in the basket. To achieve that consistent volume of grinds, I used a precise, flat and sharp metal scraper. The depth that the tool scrapes down to is based on the lip of the basket. This means It’s perfectly flat and impossible to screw up. Spinning that tool around inside the basket resulted in 0.5-1mm of grinds being neatly shaved off the top of the bed. Then, finally, I could weigh that volume of grinds and know how much there was.

Scraper

That excess coffee doesn’t even represent 5% of the total mass, so I’m happy with removing it to satisfy the rest of the experiment. This simple experiment means I could quickly and easily check the weight of a reasonable number of handles to determine consistency.

Results

Here’s the results from 15 samples of each of the three distribution styles: Tap, Stockfleth and Tamp.

Distribution Graph

From these results, it’s pretty obvious that tapping side to side and vertically (purple, if it wasn’t obvious) is superior in terms of consistency. It’s also obvious that manually manipulating the top layer of grinds (stockflething: red) is an improvement on just tamping (cyan) whatever you get out of the grinder. Let’s play with some numbers to gain some more understanding. I’ll calculate the median (central tendency, or middle of the road) of each method, and then figure out its consistency from that spot. My favourite tool for measuring consistency is called the “Standard Deviation”. Simply put, Standard Deviation tells you how spread out the results are, or how far away they are from that “middle of the road”. In this case, more spread out = more inconsistent. [Dear Math Nerds, I chose not to use Variance or the slightly more accurate Average Absolute Deviation because that wouldn’t display the results in the same units – grams – as the test was conducted in, and would likely confuse matters.] Distribution Spreadsheet

Discussion

I think it’s fair to say that if the weight is very similar across a large number of handles, then that method is consistently distributing grinds around the basket. If the weight is inconsistent then there are areas of lower/higher density that would promote/retard water flow. So inconsistency isn’t just an indicator of inconsistency itself. It’s also telling you that there are areas of unevenness. From that, I think it’s more than fair to assume that a consistent density would promote the most even flow of water through the entire bed of grounds, creating the most even extraction. This test was only conducted with 45 samples. More would of course make it more accurate. I am satisfied that there is a reasonable difference between the methods – if there wasn’t I would have collected more samples to make sure. The median column also adds an interesting element to the experiment. Tapping’s median is 0.2g higher than the others. I can’t profess to fully understand what this means, but I’ll give it a crack: If we think of the maximum amount of coffee that can be compressed into our consistent volume of basket, then it would also by default be perfectly distributed. Hitting maximum would mean there would be no areas with less coffee, because pockets of lower density implies uneven distribution. It might then be fair to say that we should be chasing a distribution method that (within the realm of this experiment) can fit the most coffee into that space the most often. The trouble with this is that the first 3 samples of just tamping yielded a higher density of coffee within that space. This leads me to believe that there could be a more superior distribution method lurking around the corner. Just tamping achieved that higher density a couple times, but can’t achieve it consistently. There’s always something better out there.

Conclusion

Acknowledging the small size of the sample, tapping appears to be the most consistent method. Stockflething is a reasonable improvement from just tamping. This by no means declares tapping the ultimate distribution winner. It just adds a tally next to Tapping on the distribution scoreboard in a game that will be played for quite some time. I’ll be continuing to devise experiments and ideas about distribution and will be inserting them in amongst my regular posts to keep things fresh and interesting! Any ideas on another good experiment? Let me know below!

 

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Matt Perger
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Matt Perger

I totally know what you mean about the coffee getting too dense to tap sideways!

In this experiment I was definitely operating with loose grounds and they were moving freely. I usually tap afterwards as well, but tried to eliminate as many variables as possible between the three methods.

Abby Holden
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Abby Holden

I agree with Camila. I use the “stockfleth” method but I never tap on the forks or anywhere for that matter until AFTER I have distributed more evenly. I also keep in mind that the coffee density with inevitably be greater in the middle before anything is done, just based on the nature of the basket, and therefore spread more coffee to the sides to account for it. It may be useful to test other ways of stockfleth, just because within it, there are so many variables. It may also be useful to do some statistical testing on your results.… Read more »

Camila Ramos
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Camila Ramos

Post-thoughts: The vertical fork-tapping of “tamping” compresses coffee bed, but at the same density variance of the initial dose. The vertical fork-tapping and horizontal hand-tapping of “tapping” compresses the coffee bed at the same density variance of the initial dose, but then reduces the variance by horizontally distributing some coffee from high density areas to low density areas. Without losing the initial dose of course, perhaps doing a horizontal distribution first, followed (or not) by a vertical distribution, might result in less density variance overall, because the grounds are more free to move before an initial compression, which may limit… Read more »

Mark C
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Mark C

Super-interesting study! I have been thinking about one aspect of the experiment: in the Discussion section you raised the issue of the first three tamp-only samples yielding a higher density, leading you to wonder whether there is a more superior distribution method. While that is perfectly feasible conclusion, it made me wonder whether the variance in density could also be due to another variable that, as far as I can tell, wasn’t controlled: particle size. The presence of fines has the potential to mess with the consistency of density if they are produced in a non-uniform way, and therefore affect… Read more »

Camila Ramos
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Camila Ramos

I would love to see results with no tap, webbed Stockfleth. Other than being my preferred method of grooming (did not partake in your poll), conceptually it makes the most sense.

Also, I wonder what variances in your experiment are due to the limitations of the methods themselves and which derive from variances in heaviness of taps, vertical or horizontal. It’s hard to replicate such a jerk force.

Justin Enis
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Justin Enis

This is radical. I was dosing this morning thinking of this post coming out when I got home. I took note that to me it seemed (by eye and very unscientifically) that tapping horizontally first, then vertically gave me the most even distribution (with my target dose as I dose into a separate glass, adjust weight accordingly then dump into the basket) as opposed to vertically followed by the horizontal tappage. I realized that this may and most likely does differ with a larger dose/overdose. Really cool to see the numbers and the SD of each method. Thanks for your… Read more »

Matt Perger
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Matt Perger

Hey! Thanks for the kind words 🙂
I know what you mean about excess coffee. I was dosing too much into the handles to begin with, so there was definitely a generous amount of grinds for me to manipulate – more than would usually be in the basket which should (in theory) benefit this method’s consistency.

And yes! Statistical relevance is the bomb. Once I do a test with a larger sample size I’ll be able to run something like that.

Camila Ramos
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Camila Ramos

Also, maybe I wasn’t totally clear in the vertical/horizontal prioritization reasoning: not in the sense that it too dense to tap sideways, but that a greater horizontal tap-leveling would be achievable without prior vertical tapping. It’s not that your grounds weren’t moving freely, but perhaps not as free as they would otherwise move.

Just playing the devil’s advocate in regard to your comment on finding another, possibly more effective & consistent, grooming method.

Evan Joseph-Piñero
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Evan Joseph-Piñero

The issues I have with just tapping, versus grooming with a hand, are twofold. The first is that, in cases where a grinder will give somewhat varying amounts of ground coffee (every grinder I’ve used, at least some of the time), unless grooming is finished with a tool, the amount of coffee in the basket will be somewhat random, and the same as just tamping as it comes. Grooming by hand, which while subject to significant human error, is essentially using one’s finger (or palm, as the case may be) as that final dosing tool. The second is the matter… Read more »

Sebastian Simsch
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Sebastian Simsch

Love the experiment!! What about a combination of “Tapping” and “Stockfleth”? Tapping up and down and then “grooming” off excess grounds horizontally? I wonder if that comes close to just tapping?
(But then again, why not tap all the way? I admit here at Seattle Coffee Works, we’re simply used to the blended “Tapping” & “Stockfleth” method… old habits die hard…)

Matt Perger
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Matt Perger

I alternated between each method, so if the grinds were an anomaly, the other two methods should have seen similar results among the first three samples as well.

Mat North
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Mat North

Perhaps the horizontal and vertical forces could be replicated mechanically, an ultrasonic plate or similar device?

tim willems
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tim willems

I second that, it seems to make more sense to first distribute horizontally with ticking the portafilter where needed on the side and compacting that evenly distributed coffee with a tap vertically instead of compacting it vertically first and making it harder to redistribute horizontally

in my experience the latter creates cracks when ticking the sides after tapping, and loses in speediness also because you have to tap twice

tick (with hand) – tap (on counter) – tamp

John Michael Cord
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John Michael Cord

Hey gals and guys, I’ve been following the discussion on this, and it has me evaluating my tamping style now. Before posing my question, here is some context: I’m using a Mazer Major E grinder to dose my shot. I’m immediately weighing and removing excess grinds with a demitasse spoon. Next, a few horizontal taps with my palm to disperse the grinds and a few vertical taps on the counter. Finally I tamp. This method has proven to be quite clean and consistent, and I’m getting faster with it. The only thing that I’m finding is that grinds tend to… Read more »

Marshall Hance
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Marshall Hance

It took me a moment to understand how the tool and measurements worked. I now see that the most even distribution would result in the least coffee removed by the tool, and thus the most coffee left in the basket, which is what was measured. I thought I’d mention this just in case anyone else got stuck there as I did.

Jesse Raub
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Jesse Raub

I’ve got issues with the idea of settling grounds. The testing here presents it as a constant, but settling is unnecessary and potentially causes fines migration to the bottom of the basket, which could affect both puck density and then, during the shot, flow rate. I agree with Camila that a finger distribution without settling would need to be tested. I also reject the notion that puck density represents even distribution and therefore the potential for higher and more even extraction. The denser the espresso puck, the higher the flow restriction becomes. The higher the flow restriction becomes, the coarser… Read more »

Karl
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Karl

Hi Matt
Can you explain ur way of tapping further?
I cannot figure how the sideways tapping wont result in a far from ideal sloping surface in the grounds.
I also think the test would be enhanced if the different methods were executed by someone who can be considered an advocate for the method in question.

Tim W or Håkon Kinn or some other such norwegian wud be the ideal executor of Stockflething for instance 😉
Not that I dont trust you but itd make it more trustworthy.

Tolga
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Tolga

Hi.
Just choose a grinder that doesn’t clump. There are huge differences.

bjeck14
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bjeck14

Hey Matt. Really nice post. Liked the layout too!

Just FYI – it’s rare to report median and standard deviation. Normally you would report the median if the data is non-normal (as it provides a better description of the central tendency). Visually, it looks like you have fairly normally-distributed results so probably best to report the mean.

Andrew Bettis
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Andrew Bettis

Response I love this discussion and the amount of thought provoking feedback. I have a few (lengthy) ideas about my theory of what is happening during distribution. I don’t think absolute visual evenness of distribution pre-tamping is the most important. Static electricity is playing a huge roll here. Think of the way ionic and covalent bonds differ. In an extraction, ionic bonds break down first, because they are not sharing an electron, they are just like north and south ends of a magnet coming apart. This is similar to the way clumps work, except with no solvent, they are constantly… Read more »

John Michael Cord
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John Michael Cord

I’ve started using a demitasse spoon to remove excess grounds, and I try to weigh every shot before tamping. The spoon allows the removal of excess with minimal human error (coffee sticking to finger or palm, and compression of grounds before tamp).

John Michael Cord
Guest
John Michael Cord

I work for a shop, so simply buying another grinder is not an option. It’s more along the lines of is this something that people are seeing happen, as far as the formation of bolders in the portafilter after tapping, and how does one rid or disperse the bolders once the bed is below the lip of the portafilter?

Matt Perger
Guest
Matt Perger

I was curious about that, thank you!

Matt Perger
Guest
Matt Perger

I’ll be publishing my method shortly.

I did my best to be impartial – I’ve stockfleth’d for many thousands of shots in my time and am certain I did it justice.

Matt Perger
Guest
Matt Perger

I believe that an even density requires the “best” grind size for the situation. Let me explain.

If there are less dense areas, then they’ll allow a disproportionate flow of water through. To compensate, you’ll need to grind all of the coffee finer. I think that’s worse than the consistent and quantifiable resistance you get from a nice dense puck.

So, aiming for a nice even distribution with this test means you’re also chasing a grind size that represents the true resistance of a perfectly even bed of coffee; not a grind size that compensates for uneven distribution.

Tyler Mastantuono
Guest
Tyler Mastantuono

Just curious why nutation was not included in any of your distribution experiments?

Some people may argue that it is a tamping method and not a distribution method, but I would argue that since it does move the grounds around in the basket it is in fact a distribution method.

It is also a very quick and cosistant method in my experience.

Curious to hear your thought on this.

Sang ho Park
Guest
Sang ho Park

I agree with your response about static being a problem in evenness of tamping, and its affect on extraction. If you get clumped ground coffees in your basket, getting a paper clip and stirring the grounds significantly reduces static. It is inevitable that you will get statics from the shear stress from grinding, but reducing static much as possible (hence less clumping) before it enters the basket would be a better solution than tamping in my opinion. But bearing in mind temperature in the grind chamber and burrs will affect statics and movement of energy.

Robert Cowles
Guest
Robert Cowles

Hi Matt,

Have you any thoughts on the value of naked portafilter visual espresso evaluation here? (This is assuming it provides any useful information at all..)
Could this be of any value in a combination experiment with the above? I.e. are there any clues in the brewing process that any of the above distribution methods is doing a better job?

Karl
Guest
Karl

Thanks for the response man and I’m looking forward to hearing bout it!

Kathie Hilberg
Guest
Kathie Hilberg

It seems to me that the arbitrary amount of times a barista might tap when they “tap the side of the portafilter with one’s palm until the grinds are perfectly leveled” would actually offer less consistency. One of the things I try very hard to get my baristas to understand is that the less they vary in their movements the less they can attribute improper extraction to their own inconsistency and more to an improper grind, brew time etc. when dialing in. If I tap the portafilter 3 times with my palm preparing one shot, and then tap it 12… Read more »

Grant Conine
Guest
Grant Conine

I am in the same boat – working with a Mazzer Robur E. There is definitely some clumping issues occasionally, especially if some of my less dedicated co-workers skip out on cleaning the grinder well at night. I tend to tap on the forks, tap on my palm, tap vertially (lightly) and then use a sort of stokfleth’s-ish move to break up boulders if they are really bad.

Andrew Bettis
Guest
Andrew Bettis

I completely agree that static electricity is inevitable due to the friction of grinding; some grinders are better than others at utilizing mechanisms to declump the espresso before it reaches the portafilter. I think you get the best results when there are no clumps at all before tamping. I like the doser that the Anfim utilizes, and I use it to declump espresso ground on other grinders, such as the EK43.

Brett Whitman
Guest
Brett Whitman

Hey Matt, I run the QC side of things over at Four Barrel Coffee in sf.. Super interested in this test and your results. I have an idea how to replicate your experiment but am wondering if you had to shape the scraper tool yourself or was it something you found at a hardware store. Also had you come across any other ways to test coffee bed density and distribution? I have been racking my brain to come up with at least one other objective test to help balance this one. You have been inspiring some of our advanced baristas… Read more »

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