The physics of brewing the perfect espresso

"Channeling" during brewing process can lead to non-uniform filtration and lower extraction yield.

See full article...

 

[Cruzmisl]

I got into espresso a few years ago, on the tail end of covid and the process of making a great shot is something I look forward to every morning. I wake up earlier just to be able to enjoy it.

What I didn’t need was another expensive rabbit hole to travel through…

 

[Wolfe Boy]

I love that coffee is at this interesting intersection of science, engineering, and culinary arts where we are able to theoretically pursue with great precision a highly subjective result.

 

[Joel622]

I've been doing the trick with the splash of water for years because it also prevents your grounds sticking to the grinder.

 

[Amarynth]

One of the best tools for minimizing channelizing and maximizing repeatability in espresso is the Umikot. It is 3D printable and uses the same principle as a spirograph to stir every portion of your espresso equally. It is available for free here: https://www.printables.com/model/481587-umikot-58mm-version-planetary-gear-spirograph-espr

I highly recommend it!

 

[LetterRip]

I'm seeing "How to trick corporations into funding your labs coffee habit".

 

[afidel]

It's worse than under-extraction, it's under-extracted overall but some grounds near the channeling are massively over-extracted, this leads to a taste profile that contains the undesirable properties of both types of bad extraction. All coffee suffers from channeling to some degree, but if you don't prep the puck correctly in Espresso it can be really bad leading to both overly bitter and overly sour notes. The ways to fight it are puck prep, pre-infusion (where you wet the grounds before applying full pressure), and a descending pressure profile (where the pressure of the heated water is decreased through the ~30-40s pour to reduce the erosion of the puck).

 

[PhaseShifter]

I love that coffee is at this interesting intersection of science, engineering, and culinary arts where we are able to theoretically pursue with great precision a highly subjective result.

You would probably love the American Chemical Society's webinar series then, at least the episodes related to food.

 

[crosslink]

I've experienced channeling first-hand, making beer. Imagine extracting the good stuff from the grain in a process where the water flows through the grain bed. I get far better yields if I introduce periodic stirring into the process than I do if I keep the grain bed intact the whole time.

 

[entropy_wins]

"Water, natures almost universal solvent" - some lecturer I had at undergrad ;-)

 

[cosmotose]

throws grenade

"They concluded that the most reproducible thing you can do is use fewer coffee beans and opt for a coarser grind with a bit less water; brew time was largely irrelevant."

edit: PLEASE DON'T SHOOT - I AM BUT A MESSENGER

 

[crosslink]

My coffee making (not espresso) involves doing the extraction in a pan, with stirring, on the stove with good temperature control (85-86C). After a 2 minute extraction the whole shebang goes into a Chemex filter.

edit: changed 56 to 86. That would be some variation!

 

[Veritas super omens]

I look forward to when we can elucidate a detailed quantum chromodynamics breakdown of the the various quarks and gluons involved in creating a great cup of espresso.

Kidding of course. I know nothing of quantum math. I do think it fascinating that we can dive deep into the science of the various factors that go into creating a great cup of espresso.

 

[Aelix]

"They concluded that the most reproducible thing you can do is use fewer coffee beans and opt for a coarser grind with a bit less water; brew time was largely irrelevant."

This goes against my experience? If it brews too fast it comes out like acidic coffee. If too slow, it’s bitter. it’s always a dance between grind size and how hard I tamp, and it changes depending on the bean. I usually end up tossing two shots when getting a new bag until I find the right combo. Maybe this does mean I am grinding too fine…

I also have a shitty Breville machine and I don’t think it’s hot enough anyway.

Funny how my entire day revolves around optimizing Java in some form. Now we have to worry about supply-chain attacks in the form of tariffs.

 

[peterford]

Highly nerdy coffee influencr Lance Hedrick is pushing people to try smaller diameter baskets and deeper coffee pucks.

Spoiler: youtube

View: https://www.youtube.com/watch?v=-lQ6OFI7EwY

 

[Albino_Boo]

I look forward to when we can elucidate a detailed quantum chromodynamics breakdown of the the various quarks and gluons involved in creating a great cup of espresso.

Kidding of course. I know nothing of quantum math. I do think it fascinating that we can dive deep into the science of the various factors that go into creating a great cup of espresso.

I'm working on Cappuccino with quantum foam

 

[lessthanjoey]

One of the best tools for minimizing channelizing and maximizing repeatability in espresso is the Umikot. It is 3D printable and uses the same principle as a spirograph to stir every portion of your espresso equally. It is available for free here: https://www.printables.com/model/481587-umikot-58mm-version-planetary-gear-spirograph-espr

I highly recommend it!

Agreed, it's an excellent tool.

 

[Ahabba]

Man, these guys found an enviable niche of physics. This reminds me: Is anyone interested in funding my proposed study of how the microbiome of various French cheeses (and their pairing with wine) correlate with perceived "flavorfulness"?

 

[terrydactyl]

From 20 years ago, a SciAm article on the science of coffee, authored by Ernesto Illy no less.

 

[Taunted Happy Fun Ball]

Man, these guys found an enviable niche of physics.

All the grad students were experimenting with optimal methods of coffee brewing anyway, but in a non-systematic way with different labs duplicating each others' research and not effectively sharing their results.

Dedicating a single lab to the problem and publishing the outcome just saves everyone some time.

 

[Aurich]

I'm sure we have some James Hoffman fans in the comments. I found this recent video he did interesting, and I thought of it when the article talked about "cafe-grade" and what we think of when we hear that, and what it really means these days.

tl;dw - Home enthusiasts are making better espresso than cafes because they're taking more time than most commercial realities allow to do it right, and the home market for equipment is giving them the tools to do it. In part though because of research like this.


View: https://www.youtube.com/watch?v=r7YtT6usTPM

 

[needSomeCoffee]

This makes a lot of sense. Been into coffee for a long time e.g. Home Roaster for nearly 20 years. The addition of water to the beans before grinding has been transformative for me -- but not related to espresso. We grind either for pour over (best way to get a non-espresso cup), or to simply use our drip machine (which makes pretty good coffee). Here are my insights (NTIM): 1) Using a good grinder, there is a lot of static electricity affecting the output. For example, with our grinder we grind into a stainless containter. Without any wetting, the static charge is so high that it is impossible to get all the grinds out of the container. 2) Wetting the ground using a mister filled with distilled water COMPLETELY rids the grind of any static affect. It all simply drops out of the container.

I cannot imagine that putting a heavily staticly charged set of grinds (and associated fine particulates) into the porta filter is a good idea. However, I should note that a "...squirt of water..." seems pretty "coarse" to me. The beans need a very light, even coating of moisture prior to grinding. We use a pretty good mister with distilled water, and shake the beans after each mist (4 total for 55 grams of beans for drip).

Final note: Coffee perfection has been a hot topic for me for nearly 20 years. I personally think this is the most illustrative technique for folks to understand the diference. This involves a "full cup" rather than espresso. I dropped off the expresso train a long time ago because I just want a full cup of really good coffee. This results in the best coffee cup I have had:


View: https://www.youtube.com/watch?v=wmCW8xSWGZY


Final note: Home roasting is the ONLY way to understand good coffee. Although not affiliated in any way, I strongly suggest you investigate Behmore (roaster) and SweetMarias (green beans -- always buy farmgate with newest release date).

HTH, NSC

Edit note: If you are paying for "premium" roasted arabica beans, you should do a quick breakeven analysis using costs of the Behmore and SM's beans. I'd guess breakeven likely within 1 year, assuredly 2 years. I've had my Behmore a loooong time, so we are making money every day vs. buying roasted beans, or Starbucks. Also love supporting direct payments to coffee growers (FairTrade is complete gaslighting). HTH, NSC

 

[crepuscularbrolly]

It's worse than under-extraction, it's under-extracted overall but some grounds near the channeling are massively over-extracted, this leads to a taste profile that contains the undesirable properties of both types of bad extraction. All coffee suffers from channeling to some degree, but if you don't prep the puck correctly in Espresso it can be really bad leading to both overly bitter and overly sour notes. The ways to fight it are puck prep, pre-infusion (where you wet the grounds before applying full pressure), and a descending pressure profile (where the pressure of the heated water is decreased through the ~30-40s pour to reduce the erosion of the puck).

Nit pick: not immersion brewing methods, e.g. French press.

 

[xee47]

As a home barista, I've pulled thousands of shots over many, many years. In my experience, channeling DOES increase flow rate. Shots will pull faster if there are channels. However, I found that the simple fix is to pre-infuse and then pause a bit to let the grounds expand. I've never had a channel with this method. I think this is pretty standard in even home machines.

 

[dave_ruff]

I got super into the science of pourover coffee a few years ago, experimenting with ratios (15:1 or 16:1?), temps, speed and # of pours (bloom + 1 or 2, no bloom, etc.), avoiding channeling, spritzing before grinding, adding salt, etc., and came to the conclusion that my 50+ yo nose really couldn't tell the difference in most cases (also hard to double blind yourself). Still, it was a fun and (mostly) harmless obsession. Currently at 16:1, 60g/240g/480g pour progression (assuming 30g coffee), with a Kalita Wave.

 

[RickRoyLeonPrisZhoraRacha]

I would have bought a fancy espresso that was made in Europe but I couldn't afford it/justify it. Then I looked at an Aussie espresso machine, the top of the line Breville, but again couldn't justify it. Then I visited seattle coffee gear and then found a refurb Saeco (now Phillips) for under $500.
I may make the grind more coarse but I can't change the amount of water use. I have cool, filtered water going in, and usually beans less than a month old.
Its just good enough that we no longer spend $$$ at coffee shops weekly. Add some milk, non-milk or even chocolate milk to the froth-hopper and perfect latter or cappucinos. Or I like make the mocha with adding milk then zap for 40 sec in microwave for nice hot mocha latte.

 

[Echohead2]

no mention of over-extraction.

 

[dmsilev]

I look forward to when we can elucidate a detailed quantum chromodynamics breakdown of the the various quarks and gluons involved in creating a great cup of espresso.

Kidding of course. I know nothing of quantum math. I do think it fascinating that we can dive deep into the science of the various factors that go into creating a great cup of espresso.

There is, and I swear I’m not making this up, a software package called Quantum ESPRESSO which is a popular tool for ab initio quantum calculations of various materials.

 

[Aurich]

However, I should note that a "...squirt of water..." seems pretty "coarse" to me. The beans need a very light, even coating of moisture prior to grinding. We use a pretty good mister with distilled water, and shake the beans after each mist (4 total for 55 grams of beans for drip).

Whatever works for you is what's best. But I just give my beans (15g) a couple quick mists with tap water from a cheap little atomizer and check them into a Baratza Encore and I have no static problems.

Not saying you should change what you do, just bringing it up to say that doing it a non-fussy way works fine for me, and people should not feel like if they aren't being meticulous it's not worth doing.

I do a v60 pourover, 15g coffee to 250g water. It works for me. Others might find some other ratio is to their preference. That's part of the fun of doing it yourself.

Final note: Home roasting is the ONLY way to understand good coffee. Although not affiliated in any way, I strongly suggest you investigate Behmore (roaster) and SweetMarias (green beans -- always buy farmgate with newest release date).

This is an enormously silly and snobby and weird statement. It is most certainly not the ONLY way, don't be ridiculous. Maybe it's a GREAT way! Not the same as "only".

As noted above, I'm sure it's part of the fun of doing it yourself, and I imagine you've got something that works well for you, and that's great. But acting like nobody can understand good coffee without roasting their own beans is preposterous.

Coffee is good. I'm drinking coffee right now. I enjoy the science and fun of it. But the mysticism side can get very tiresome.

Go Get Em Tiger sources really good coffee, roasts it fresh for me, and I grind it myself. I'm quite confident I don't need to be doing my own roasting for some reason, they're extremely competent and knowledgable coffee people who do a great job.



At the end of the day it's just coffee though. The effort you put in should only match the value you get back out.

 

[MK1_halfive]

There is a temp curve, hottest (bitter) at the beginning, cooler at the end (acidic) Three seconds of blonding at the end balances the bitter vs acidic. Adjust grind for 13-17 seconds for a single shot.

 

[naive_cynic]

I've experienced channeling first-hand, making beer. Imagine extracting the good stuff from the grain in a process where the water flows through the grain bed. I get far better yields if I introduce periodic stirring into the process than I do if I keep the grain bed intact the whole time.

It's been a long time since I've made beer, but I used to get good results with batch sparging and great results when I didn't sparge at all. It's also quicker and simpler.

No, you're not going to be as efficient as you would with be with a sparging arm so you need to use more grain. I felt the cost was minimal.

Like needSomeCoffee above, I roast my beans at home with an aging Behmor. Like Aurich, I disagree that this is the only way to understand coffee,--but I always have fresh coffee, my roasts are high quality and I save money (compared to what I'd spend for beans of comparable quality, anyway).

I am kind of concerned about what I'm going to do once my Behmor finally dies; the people I bought it from went out of business and I think Behmor itself has had some problems.

 

[stratology]

...¨When the dry coffee puck is hit with water under high pressure¨...

So do they deliberately disregard pre-infusion, which means that the puck is already wet before the high pressure starts?




..¨and a cafe-grade espresso machine, tricked out with a pressure sensor, flow meter, and a set of scales. The entire setup was connected to laboratory laptops via a microchip and controlled with custom software that allowed the scientists to precisely monitor pressure, mass, and water flowing through the coffee.¨...

AFAIK, these are all parameters that are among the many you can control with a Decent espresso machine out of the box. The measurements are sent to an Android tablet that's part of the Decent, again using their stock software.

The Decent is not a 'cafe-grade' coffee machine, it's specifically built for home enthusiasts...

 

[KingKrayola]

I'm seeing "How to trick corporations into funding your labs coffee habit".

Small engineering business owner here, with a team who 'quite' like coffee. I'm already thinking of adding an extra PLC to our next order for some PID control, and I've been looking for an excuse to get a Labview licence and DAC...

Anyone tried measuring in-line brew pressure? In theory the relief valve should make it the same flow or no flow, but I wonder if our solenoid pump is keeping up?

 

[methodmadness00]

I look forward to the day when all these findings are incorporated into a massively over-complicated and over-priced at-home espresso machine with flow sensors, built in puck CT scanners, and spectrometers that requires a monthly subscription to function and gets bricked when the overfunded Silicon Valley startup manufacturing it inevitably goes bankrupt...

 

[Unimportant]

This goes against my experience? If it brews too fast it comes out like acidic coffee. If too slow, it’s bitter. it’s always a dance between grind size and how hard I tamp, and it changes depending on the bean. I usually end up tossing two shots when getting a new bag until I find the right combo. Maybe this does mean I am grinding too fine…

I also have a shitty Breville machine and I don’t think it’s hot enough anyway.

Funny how my entire day revolves around optimizing Java in some form. Now we have to worry about supply-chain attacks in the form of tariffs.

I love my $300+ Breville.

I certainly couldn’t afford one of the super-premium machines

 

[jonah]

Wasn't there a study a year or two ago that said that a single spritz of water wasn't actually optimal?

I've been spritzing ~4-5 times for years, mind you, just because it cuts static down, but I recall feeling validated that adding more water pre grind was actually better.

 

[Unimportant]

Regarding static buildup:
My grinder discharges ground coffee into a metal cup. I can see some charged grounds clinging to the side when I’m done. I touch the metal cup to my grounded metal sink, then stir the grounds with a metal spoon for about 15 seconds.

Shouldn’t that fix the static issue?

 

[the.mighty.oracle]

From the perspective of a geotechnical engineer, everyone seems to be ignoring the 1st or 2nd most important factor for the channeling, which is the grain size distribution. You want a compactible distribution of particle sizes. Having a uniform coarse grind will certainly help avoid channeling, but I question the cost of doing so. Having an ideal gradation of particle sizes should allow substantially higher consolidation prior to water addition. Having a bit of water in there at that point will also help, so a strong hand on the pre-grind water addition may help, but very low initial pressure will do far more. Allowing the time for the expansive organics to swell will be the 2nd critical factor. The ideal gradation would have a nice strong "S" shape to the log graph per below. Maximum and minimum particle sizes should fit to your range, but compactible soils will have that S. Finding the right grinder to create that gradation or particle sizes, perfecting the stirring, and consolidating with cycled or vibrating methods are the name of the game to minimize channeling in soils whether they are expansive, organic, partially soluble, or whatever else.

 

[spopepro]

I think the major advantage of home roasting is getting to brew in roughly the same age range every time. I don’t roast (too many world-class roasters around me to make it worthwhile) and so I know that I have to slightly change the grind and dosage as it gets further away from the roast date. I find I get the best pulls 3-4 days after roasting, and good results until about day 12.

I am surprised they did all their testing on a single shot. I find it much harder to get good pulls, and I don’t really know anyone who doesn’t pull doubles as default. It fits in with the narrower basket crowd’s thinking too.