Posted Wed May 25, 2011, 6:58am Subject: Aeropress - Hypothesis: Why it can't make "espresso"
I've seen lots of discussion over the years here and on other forums about whether an Aeropress can make "espresso" or not, and if not, why.
I've also seen the explanations that the method of espresso cannot be duplicated by other means, that the fine-ness of the grounds for expresso, or the existence of crema and emulsion of oils is why an Aeropresso and an espresso can never be the same, but no real explanation of what the mechanism is that prevents the Aeropress from making espresso.
I think I may have figured out why, and it does indeed have to do with the method of extraction for espresso vs. other brewing methods.
The inventor of the Aeropress has showed lots of data about the strength of the brewed coffee, approaching levels of espresso (generally >6% strength). There is little data, however, showing actual (either backcalculated or directly measured) EXTRACTION of the coffee. To determine this, the calculated TDS is needed as well as the pre-brewed mass of the coffee grounds.
As we all know, espresso and coffee have their best flavor profile when the grounds are properly extracted, somewhere between 18%-22% of the potentially 30% available solubules dissolved into solution in the drink we call coffee (or espresso). I believe I now understand why the Aeropress makes a damn good cup of coffee IF used to brew normal or maybe double strength coffee, but does not and probably cannot achieve "espresso".
Some definitions:
Espresso refers to the method of extraction. This method uses pressure (~130PSI/9bar) and high temperature (200°-205°) water, and relatively little water, along with a very fine grind, to yield a solution with somewhere between 7%-20% strength. The method controls the strength of the final drink and the extraction by the dosage and the time used to pull(push?) the water through the grounds. A good machine maintains the temperature of the press water at a consistent temperature.
Extraction is simply the mass of the coffee removed from the grounds as a percentage of the starting coffee mass.
Strength is the mass of the coffee removed as a percentage of the resulting drink. Typical coffee ends up around 1.25% strength, I seem to prefer mine around 1.35% or so. Europeans tend to like it approaching 1.5% (strong by most of our standards). Espresso ends up usually ~5%-7% (for a PBTC produced automatic *$s machine) to >7% up to maybe 20% strength for professional baristas.
Brew ratio is the percent mass of coffee to mass of brew water (as opposed to espresso brew ratio, the ratio of ground coffee to yielded drink).
Ideally, whether coffee or expresso, the extraction target is the same - that nice balanced 20% of the coffee mass dissolved into a liquid. Much more and you get the distinct bitterness of burnt cellulose, less and you leave components of the flavor profile behind. Some espresso is extracted above 22%, but not much more, and is usually easy to tell if espresso is underextracted.
So, I reasoned that the first two constraints on the Aeropress to produce an "espresso-like" drink are: 1) it must be able to achieve 20% extraction 2) after that, it should produce a liquid with that 20% extraction that could be up to 10% strength.
I have proved to myself that if used inverted, with extended contact times, proper water temperature, and proper grind levels, the Aeropress can make normal to double strength (up to about 2.7%) coffee with full flavor profile and full 20% extraction of the grounds. It CANNOT do this with 175°F water or if used according to instruction (producing smooth but underdeveloped/underextracted coffee).
Over the last several weeks, I have been tracking extraction and brew ratio, and yielded strength. I can produce coffee strengths approaching 7-8%, and I can get extraction to >18%, but it seems I cannot do these AT THE SAME TIME.
What I'm finding is that as the brew ratio approaches 15%, the extraction becomes very difficult to keep above 18%. Dropping from 205°F water to 175°F water drops the extraction by a whopping full percent. At a 25% brew ratio, about the best I can do is a 17% extraction for 205°F water to about 15.5% extraction for 175°F water.
I can increase the strength of the coffee by increasing the brew ratio, but the extraction drops even further (below 15%) - I get more coffee solids in less brew water, but cannot extract enough of the good stuff to have something that actually tastes good.
I will have to experiment some more, but the closest thing I've found is 15% brew ratio (18g coffee to 120g water) at 205°F water and >2min contact time. This was about 18% extraction and a strength around 3.2%. Excellent cup of concentrated coffee, and really great cup of coffee when cut 2:1 (add approx 120g) to bring the strength to a strong but scrumptious 1.5%.
A couple of observations - the extraction is helped by finer grind, but not as much as I was hoping. I haven't gone all the way to espresso because of the difficulty for pressing. I use <drip or on par with 1200-1500 particles per bean.
I believe one issue is the thermal mass of the single-cup brew in the Aeropress. I tried brewing at 150°F water once, just to see. The extraction was horrible, around <10%.
Therefore, I think the decreasing temperature during contact time (something that a vacuum brewer or an espresso machine, or even the single cup brewers don't deal with) is the culprit here. Room temperature grounds mixed 1:4 with high temp water means a coffee slurry of about 180°F and drops quickly below 150°F during contact time - EVEN if the aeropress is pre-heated (which I have been doing). This is probably prematurely terminating the rate of extraction.
I think this dabbling may shed some light on why the Aeropress has yet to produce a beverage that has a running chance of being close to espresso - it is nearly impossible to achieve both the extraction and strength (20% extracted solids at ~9% strength).
A look at the SCAA and SCAE charts and you see the brew control charts only go up to about 9% brew ratio - even then, you see that it takes making a beverage with 1.65% strength to even TOUCH 18% extraction at a 9% brew ratio. The slope (strength:extraction) increases as the brew ratio goes up, so trying to achieve the "sweet spot" of 20% extraction for a brewed non-pressurized method with no temperature control at 9% strength may not even be achievable. Espresso does this by high pressure and high and constant temperature brew water through very fine grounds. IF one could determine the line for 50% brew ratio - it may not even cross the extraction zone at any mathematically reasonable concentration.
Essentially, as some point there's just not enough water with enough energy at high brew ratios in the Aeropress to get the extraction done properly. I think this level is approached around 15%-20% brew ratio.
Very fine grounds on an Aeropress (with normal filters or metal filters) is not feasible because of the press force limitation or clogging of metal filters.
It just may be simply beyond the capability of this device to make a fully (i.e 20%) extracted high strength (i.e. 9-10%) coffee.
Not to say the Aeropress is anything less than an excellent brewing method - for very little money it provides a terrific level of control for brewing normal and double strength coffee - it just ain't espresso, and there are some physical limitations.
I have also given some consideration to split brewing, though I am skeptical. I would have to figure out if there is a water volume that actually works properly to end up with full extraction but end result of 9% or so.
Split brewing is partial extraction as a first brewing step, then essentially brewing the same grounds a second time to extract the remaining. This method is used in the liquid concentration industry to extract the "smooth middle" of the coffee (that is also somewhat absent some character) - essentially what the Aeropress does at recommended brew ratio. Then a second brewing step to extract the "half-n-half" portion of the extraction, where you flirt with overextracted parts and the rest of the flavor profile - but this volume of extracts can be used to increase the yield, and partially control the taste of the final product.
Lot of work, lots of words, I know, but shoot me - I'm simply curious.
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
germantownrob Senior Member Joined: 2 Dec 2007 Posts: 2,043 Location: Philadelphia Expertise: I love coffee
Espresso: Duetto 3, A Dead Oscar Grinder: Vario-W, Preciso w/Esatto,... Drip: Brazen Roaster: Diedrich IR-1, HT B
Posted Wed May 25, 2011, 7:49am Subject: Re: Aeropress - Hypothesis: Why it can't make "espresso"
Simply put espresso yields around 20% extraction and so does a cup of brewed coffee, it is the volume that is different. Without 9bars+/- at 195-205f I just don't see how you can come close to 1-2oz at 20% with any other brew method.
I would be very curious to see the findings you may come up with if you experiment with cold brewing coffee. I do it in 1/2 gallon mason jars at a 4 to 1 ratio in fridge for 12 hours then pour through a filter, never found the need to spend any money on this method of brewing.
Posted Wed May 25, 2011, 8:12am Subject: Re: Aeropress - Hypothesis: Why it can't make "espresso"
FYI: For those not in the know, this specific topic had been beaten to death ad nauseum in the aeropress thread "Aerobie Aeropress"
Len
"Coffee leads men to trifle away their time, scald their chops, and spend their money, all for a little base, black, thick, nasty, bitter, stinking nauseous puddle water." ~The Women's Petition Against Coffee, 1674
If you would point me to which of the 218 pages and 2,200 posts explicitly describe WHY, or anything that shows measured extraction, I'll read it... again. I've read through all of the discussion (yes, all of the posts) and specifically the posts where Adler and Scott argue about whether it makes espresso or not. I was reasoning that if proper extraction and strength are met, these are at least necessary conditions FIRST. Then we could determine what the differences were between espresso and Aeropresso.
I see a number of posts from Adler where he works a Brix-scale sugar refractometer, lots of discussion of strength - no back calculations of extraction. There are even a few where he tries some different grinds and gets extractions from 15% to 20% - YET he tastes no differences. I find this in direct conflict with my own experiences (and in fact one of the reasons I started measuring extraction).
Lots of claims of 20% extraction, yet I can't seem to duplicate this - and my taste buds confirm this. If you follow the instructions, the coffee concentrate is strong but underextracted. If you modify the parameters to get espresso strength result, the coffee will underextract. If you properly extract, the best strength it seems you can get is about 3%.
I think the key is a misunderstanding of the calculation by Adler once he had a brewed %TDS - he used the backcalculation with the BREW water, not the mass of the resulting drink. You can't do that, even if you think the water in the puck "extracted" anything - it isn't "extracted" until it makes it to the cup and subsequently to the dehydrator or gullet.
I think I've discovered that the Aeropress naturally prevents overextraction - specifically because of the thermal properties. The extraction terminates with high brewing ratios before the coffee can overextract. The grind can not be much smaller than a bit less than drip, or you can't press it - so you're limited for very small grind size, lest you find your Aeropress plugged or unpressable. The paper filter will become a drip brewer in 45-60 seconds, so you can't have excessive contact time (if brewed normal orientation). Especially so since the instructions promote 175°F brew water - in a world where crappy overextracted and overroasted coffee is ubiquitous, "not overextracted" or even "underextracted" coffee from even dark roast coffee is really a breath of fresh air.
Unfortunately, this also mutes some of what makes varietal single-origin coffee an artisan endeavor.
germantownrob Said:
Simply put espresso yields around 20% extraction and so does a cup of brewed coffee, it is the volume that is different. Without 9bars+/- at 195-205f I just don't see how you can come close to 1-2oz at 20% with any other brew method.
I would be very curious to see the findings you may come up with if you experiment with cold brewing coffee. I do it in 1/2 gallon mason jars at a 4 to 1 ratio in fridge for 12 hours then pour through a filter, never found the need to spend any money on this method of brewing.
Point 1 - EXACTLY. You can't, yet I haven't found where anyone explains why.
Question 2 - I haven't "cold brewed" using the Aeropress. I have made small batches of cold brewed coffee, and it tends to be not much more than 16% extraction, even after 24 hours contact time. It also tastes a lot (using the same beans) like an Aerocano brewed according to instructions. (I do use the Aeropress to separate out the grounds - very useful there!)
That's a 25% brew ratio (50g coffee : 200g water), fine grind (about same as Aeropress), 24 hour refrigerator contact time. It yields a coffee that is about 6% strength, which is decent when diluted 3parts to 1. Similar to Aeropress according to directions - nutty, smooth, low bitterness but very little "character". Can't really tell the difference between a Kenya, Ethiopia, Guatamala or Columbia.
Cooler temperatures extract SOME of the desirable flavors, accentuates nutty flavors and those associated with lighter oils, and mutes floral character and fruit notes but ALSO mutes bitter oil extraction (if not eliminate it entirely) along with muting astringency.
EricBNC Said:
It cannot make espresso because it is not an espresso machine.
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
germantownrob Senior Member Joined: 2 Dec 2007 Posts: 2,043 Location: Philadelphia Expertise: I love coffee
Espresso: Duetto 3, A Dead Oscar Grinder: Vario-W, Preciso w/Esatto,... Drip: Brazen Roaster: Diedrich IR-1, HT B
Posted Wed May 25, 2011, 12:05pm Subject: Re: Aeropress - Hypothesis: Why it can't make "espresso"
Netphilosopher Said:
Point 1 - EXACTLY. You can't, yet I haven't found where anyone explains why.
Question 2 - I haven't "cold brewed" using the Aeropress. I have made small batches of cold brewed coffee, and it tends to be not much more than 16% extraction, even after 24 hours contact time. It also tastes a lot (using the same beans) like an Aerocano brewed according to instructions. (I do use the Aeropress to separate out the grounds - very useful there!)
That's a 25% brew ratio (50g coffee : 200g water), fine grind (about same as Aeropress), 24 hour refrigerator contact time. It yields a coffee that is about 6% strength, which is decent when diluted 3parts to 1. Similar to Aeropress according to directions - nutty, smooth, low bitterness but very little "character". Can't really tell the difference between a Kenya, Ethiopia, Guatamala or Columbia.
Cooler temperatures extract SOME of the desirable flavors, accentuates nutty flavors and those associated with lighter oils, and mutes floral character and fruit notes but ALSO mutes bitter oil extraction (if not eliminate it entirely) along with muting astringency.
I am going to stick with the answer to Why is the 9 bars of pressure. From what I have read prior to 1938 espresso was made with steam and water and was pretty awful tasting, then came the piston based machine that solved that "burnt taste".
Thanks for the info on cold brew. I use beans that the profile did not come out the way I liked or beans that are getting on the old side for making cold brew for iced coffee. I never really like iced coffee until I started to cold brew it, I do not dilute it with water I just add ice and it does it all by itself. It is win win to me, the beans would have gone in the trash otherwise.
Either insufficient pressure or insufficient temperature long enough to extract with minimal water. For a double shot at 9% strength, the barista is trying to extract about 5.5g of coffee solids from 25-30g of grounds using a bit more than 60ml-70ml (about 60g-70g give or take) of water.
There isn't enough energy in 70ml of water to do this as an Aeropress - the 25g of ambient temperature coffee drops the temperature of the total brew enough to stop extraction before it is fully complete.
I have not, however, tried a 10 minute contact time, but cold brewed coffee doesn't fully extract, so why would cooled coffee? Within 1 minute, the contact slurry will be below 130°F, and in 10 minutes will be close to ambient temperature.
One thing I have also considered is continued heating during contact time, and Aeropressing the result. Essentially, take about 110g-120g of boiling water, add 30g of fine ground coffee, continue to heat/stir this on stove for 2minutes at 205°F, SUB boiling (and expect about 10g-20g of water maybe evaporates during this process), THEN pour the slurry into an Aeropress to separate out the grounds. This SHOULD enable a full 20% extraction (or maybe more) and result in 60g of 10% strength... of something (but whatever it is, for the first time it will approach the extraction and strength of a 40%EBR double shot espresso).
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
Posted Thu May 26, 2011, 12:02pm Subject: Re: Aeropress - Hypothesis: Why it can't make "espresso"
OK, so it's the pressure that allows that final extraction toward target 20% (or more).
I tried a fine grind (about as far as my patience would allow me to grind 30ish grams in about 4-5 minutes), started with 118g of water (ending with 92.2g after the hi-temp contact time) for a brew ratio of 32.2%. I brought the water to boiling in covered container, then transferred to hot pan on low.
Added the grounds and stir/simmered for 2:00 (bizzare, I know, but still trying to duplicate "claimed" results). Transferred all of the slurry to an Aeropress, and after a very patient minute of pressing (I mentioned fine grind) I produced 54.9g of a very decent aroma, thick substance that resembled espresso with the crema stirred into it.
The resulting extraction of this crazy stunt ended up to be 17.8%, and the strength of the result required right around 300g of added water to bring it to about 1.5% strength. The backcalculated strength of the initial press is 9.8%.
So, here is the closest I have ever gotten to producing a 20% extracted 9-10% strength beverage, but had to go to extraordinary measures just to get the extraction on the border.
The result was a surprisingly excellent cup of nicely balanced coffee (India Western-Ghats hi-elevation), smooth but a shocking amount of varietal flavor, lots of nutmeg and a mild toffee with a hint of orchid in the nose - on par with a very well prepared cup of the coffee normally, but with more complexity. Honestly, I wasn't expecting much, so I was pleasantly caught off guard from the first sip.
My conclusion is that under normal atmospheric conditions with only the initial heat of the brew water available during brewing, full extraction seems limited by about 5-6% strength. Maybe this is the saturation limit of 180°F and cooler water as a solvent - the point at which the water can't bring much more of the coffee solids into solution.
It is possible to push the extraction further by adding heat, but then one must begin (I know, just NOW?) to ask oneself why. Unless I end up with an espresso machine or someone who is a top notch barista, there is little sense in continuing further - this last attempt was an unexpectedly excellent-tasting result, VASTLY superior anything I've had resembling an Americano at *$s. That doesn't prove that the Aeropress makes espresso.
If anyone thinks they have been able to produce a 20% strength drink with 20% extraction with an Aeropress, they haven't. If so, please post the brewing parameters so I can duplicate.
I did see posts in the past where Adler claims he can produce ANY strength beverage with the Aeropress (even up to 23%), but I just don't see this as a meaningful result, and nearly impossible to do with proper extraction. This was supposedly measured with a brix-calibrated refractometer, but one must question whether this is accurate. The puck absorption for an Aeropress is about 1.2 - 1.5 (meaning of the brew water used, 1.2-1.5 TIMES the mass of the coffee grounds is stuck in the puck). This implies the brew ratio limit is around 80% to produce ZERO brewed product
In Adler's proposed example, he said "48g of coffee and very little water" which to me means a minimum of 85 grams of water used. The only times I get extremely high strengths, my extractions are pitiful (around 14%) and the result is nasty stuff barely resembling coffee.
One recipe that I keep coming back to, it produces a decent 10ish oz of excellent coffee: 22.5g coffee 115-125g of 205°F water (just off boil) Grind slightly more than drip (not quite Press Pot - somewhere in between) Brew inverted, 2:00 contact time Flip and press in about 30 seconds through a 5, 10, or 15 micron polyester felt filter
Produces about 90g of stuff around 5% strength. By itself, very rich, full flavor profile. Reminiscent of weaker espresso, without any crema (or the crema stirred in) and served at a low temperature.
Add 210g (or ml) of hot water and you get a good smooth strong cup of ~1.5% strength coffee with correct extraction and full flavor of the bean.
NOTE: this is NOT according to Aeropress instructions. Using low temperature water makes an underextracted and weaker coffee in the end.
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
Posted Wed Jun 1, 2011, 6:41am Subject: Re: Aeropress - Hypothesis: Why it can't make "espresso"
Some more fuddling around:
I tried thrice to duplicate Adler's high strength experiment. I don't think that full extraction is possible with 175°F water.
Adler claimed to produce 23% strength (as measured with a Brix-calibrated and correlated refractometer) "Aeropresso" with 48g of coffee and little water, implying the extraction was correct (around 20%)
While unusally high strength can be achieved with an Aeropress, it doesn't seem possible to extract much more than about 6-7g from 50g of coffee no matter how much water I use at 175°F (at extremely high brew ratio). I'm doing a very fine grind, (press takes almost a minute), and even stirring for 30 seconds (20 seconds more than recommended).
The result is in the cup - nutty and slightly sour, all the elements of underextraction. Less water seems to imply less extraction.
49.7g Coffee : 100g water 6.9g extracted, 13.9% extraction. 48.7g Aeropresso produced at about 14.2% strength. Required 450g of water added to get to normal strength by taste.
50.1g coffee : 86g water 6.7g extracted, 13.4% extraction 37.7g Aeropresso produced at about 17.8% strength. Required 500g of water added to get to normal strength by taste.
49.8g coffee : 74.3g water 6.2g extracted, 12.4% extraction 26.4g Aeropresso produced at about 23.5% strength. Required about 450g of water added to get to normal strentgh by taste. This batch was especially poor - a very weird flavor profile similar to earwax. Blehchhh! (reference taste would be one of the Jelly Belly "Bertie Bott's Harry Potter All Flavor" jelly beans - earwax flavor). Vaguely remniscient of chewing a No-Doz pill without the mint essence.
Unexpectedly, the absorption ratio in the puck was hovering around 1.1 (i.e 1.1 X the grounds original mass was water stuck in the puck) for all three batches. This is much lower than when using more normal brew ratios. Because the resulting brewed coffee is so small, I did spend a lot of time pressing the puck to get every possible drop, so this may be part of it.
Conclusion: Yes, you can produce high strength brew with an Aeropress. However, the result is so hopelessly and meaninglessly distant from proper extraction that it can barely be called coffee.
Raising the temperature MAY be able to get some more extraction (and thereby higher strength) but the boiling point of water and the huge ratio of ambient temperature grounds mass to water even "just off boil" is a limitation that will not allow this to compensate for lack of high pressure during brewing. It appears this pressure during expresso extraction is what allows very small amounts of water to properly extract the full and proper amount (about 10g) of solids from the coffee with espresso.
------------------------------------------ ----------------------------------------- Le café doit être noir comme le diable, chaud comme l'enfer, pur comme un ange, et doux comme l'amour.
"There is no right answer with coffee. There is only the elixir in your cup at the moment you partake."
"...I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;..." - Lord Kelvin RECIPES thread => http://www.coffeegeek.com/forums/coffee/machines/585708
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