Posted Tue May 8, 2012, 9:24am Subject: Coffee Extraction Discussion, Questions for the membership:
So, I've devised and run an experiment to test both my coffee brewing skillz, repeatability, and generalized taste.
My first target was to run three levels of "extraction" (by both varying grind and contact time), three different brew ratios at approximately the same total brew mass give or take the limitations of the brew device. These levels were to approximate underextraction, mid to slightly strong extraction, and something that is OVER extracted.
I chose to use my Aeropress, inverted, a scale with resolution to 0.01g, and my Bodum Bistro Grinder Click Here (andlots.com) The "pourover" icon is considered 0, there's an espresso icon at "-5", and a press pot icon at +6.
My filter is minimal absorption, uses what I call a "supported" Aeropress filter, and consists of a the paper Aeropress filter, on top of a cut circle of "gold tone" coarse filter, backed up by a coava disc and then the filter cap. I find the gold tone mesh helps keep the paper filter from restricting the coava, and the coava provides needed support to keep the paper filter from pushing into the filter cap holes and blowing open. It seems to provide better clarity than an aeropress or coava alone, and less fines than either.
(Before I started, I did try just a paper filter without the gold tone mesh on top of a coava disc, but ended up with occasional heavy press resistance, which I assume if the paper filter fibers clogging the holes. I felt I'd be more consistent and better off with the triple layer, and I think the decision is the right one).
I decided on 1 replication, then a randomized run order. That's 18 cups of coffee, all measured to hundredth of a gram, coffee, brew mass before pressing, the coffee in the filter, the produced coffee, the mass of the spent coffee, and the VST strength. Don't forget to sample the product and decide whether it has the characteristics of extraction.
So the question is this:
If I have a given method of extraction (grinder setting, contact time, temperature of water, same coffee), and the ONLY thing I change is the Brew Ratio, what should "extraction" do?
Example:
6% Brew ratio, (16.66 g water : 1 g coffee). Grind to a very fine grind, then contact for 480seconds (8 minutes). I'll achieve a particular extraction.
Then, I use a 12% Brew ratio (8.33g water : 1g coffee), same grind, same 480seconds contact time.
Then, I use an 18% brew ratio (5.55g water : 1g coffee). same grind, same 480 contact time.
So, only difference being brew ratio, what should the EXTRACTION do? Should it stay the same, go lower with higher brew ratio, or get higher with brew ratio?
Change the parameters to a 3 minute contact time, and grind to slightly more coarse, and brew the same three brew ratios.
If you use the normal brew control charts as a guide, this would imply that the strength is pretty much predictable given any one of the brews. If you use these three brew ratios, and you have a particular strength, then the extraction would be predicted.
I know what they TASTE like (both as produced and also when diluted to equivalent strength of around 1.2%, if possible), and I have some interesting notes on the differences between diluted vs straight for a "normal-strong" brew, but I wanted to see if anyone had any thinking on what extraction happens at different brew ratios.
Thanks!
------------------------------------------ ----------------------------------------- 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
jpender Senior Member Joined: 11 Jul 2011 Posts: 428 Location: California Expertise: I like coffee
Grinder: Kyocera CM-50 Vac Pot: S/S Moka Pot Drip: Aeropress
Posted Wed May 9, 2012, 5:10pm Subject: Re: Coffee Extraction Discussion, Questions for the membership:
Netphilosopher Said:
So the question is this:
If I have a given method of extraction (grinder setting, contact time, temperature of water, same coffee), and the ONLY thing I change is the Brew Ratio, what should "extraction" do?
I think it will decrease with increasing brew ratio.
Ignoring possible temperature effects, as the brew ratio increases there will be a larger proportion of liquid retained in the grounds. Regardless of brewing method there will be some amount of solubles trapped in that liquid so the extraction will decrease.
The brewing control chart assumes a constant ratio of liquid retained per unit measure of initial coffee, something around 2.3. This results in the prediction that as the brew ratio approaches 1/2.3 (about 43%) the extraction will approach zero as all the liquid is retained in the grounds. I'll bet that's not too far from the truth.
But when you ask what extraction should do I think you're after something else, some other metric that corresponds to optimal extraction for a given set of parameters. Maybe there's a nice way to do that, maybe we end up with a bunch of different charts. Consider the guy who sieved his grounds to obtain a very narrow grind profile. His optimal extraction for a given set of brewing parameters changed significantly. What should his extraction have done?
Posted Wed May 9, 2012, 8:17pm Subject: Re: Coffee Extraction Discussion, Questions for the membership:
Netphilosopher Said:
If I have a given method of extraction (grinder setting, contact time, temperature of water, same coffee), and the ONLY thing I change is the Brew Ratio, what should "extraction" do?
The answer seems obvious, which makes it seem like you're probably asking a trick question. If so, I can't figure out the trick.
Anyway, I would definitely say that as the coffee-to-water ratio increases, the extraction yield decreases. This would be true whether you calculate Extraction Yield (beverage mass x %TDS / coffee dose) or "Adler Yield" (brew water x %TDS / coffee dose).
Posted Thu May 10, 2012, 5:01am Subject: Re: Coffee Extraction Discussion, Questions for the membership:
That's my thinking too (decreasing with increased brew ratio) - and the reason I decided to map out the "taste space" (did I mention I did systems analysis early on - multidimensional optimization, etc.). Specifically over defining the design space for brew ratio, absorption, extraction and strength.
If you look at the brew charts, I reasoned that with a well-controlled and replicated brew (input variables) I can get the absorption and the resulting strength - then consult the brew charts.
Problem is that all three brew ratios (just did the low BR and high BR once again to confirm) using the overextracting recipe TASTE overextracted. In fact, when diluted to same strength (about 1.2%), I ended up having to look under the cup to determine which one was which (I had guessed the correct one, but only had about 60% confidence I had the right one).
The "classic" brew charts indicate going from slightly overextracted to severely underextracted (22%ish extraction at 6g/100g to <16% extraction at 18g/100g). This is definitely NOT the case - I have underextracted samples too, and they have a VERY characteristic taste.
I'm understanding more and more about the brew charts, including how they were developed. I'm actually thinking of putting this info together into a single document to post online - a more favorable way to present the findings and how I conducted the experiment, and allow people to duplicate it should they so choose.
Another curious thing - I've been also mapping out my Melitta BCM-4C with different brew ratios. I'm limited by the basket size and full brew cycle, so I have to reduce the brew water and can't go much more than maybe 10% brew ratio - BUT in nearly every case, this little device is (by both taste and by the brew charts) OVER extracting, even at coarser grinds that should be trending toward underextracting. Even using standard grind for drip as ground by a Ditting, at 6% brew ratio it's not uncommon to get strengths above 1.55% TDS.
So, Andy, no tricks. Just trying to interpret what I found and reconciling it with what I taste and the "conventional" knowledge of controlling the brewing process. I expected reduced extraction and was absolutely shocked to find that the normal-high(ish) brew parameters all tasted pretty much the same (when diluted to similar strength) - MAYBE a bit less extracted for the 18% brew, but not severely underextracted as the brew charts would predict.
I'm unsure that anyone else has tried this, either, so I figured that if anyone had they'd pipe up to a question like this.
I was also recalling that in the refractometer thread, you did attempt an "overextracting" recipe that didn't technically overextract - did you taste it? I assume you would but at the time I can't recall if you did or not, and if it had overextracted characteristics or not.
------------------------------------------ ----------------------------------------- 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
D-Setting Grind and contact time -2 and 480 seconds (expected to be heavily overextracted) +1 and 180 seconds (expected to be 20-22% extracted) +6 (press pot) and 120 seconds (expected to be <18% extracted)
I did a full factorial with one replication, randomized run order. (that's 3 brew ratios X 3 brew parameter levels X 2 measurements each - or 18 cups of coffee).
All runs measured to 0.01g, and scale checked with a 500g OIMI class M2 cal weight (allowed tolerance ± 0.08g) and recalibrated if the reading is more than 0.1g off (rare, usually reads within 0.01g of 500.00g).
Weighed the empty cap with filter, aeropress ready to accept the coffee, and the cup for each run.
Added the ground coffee to the aeropress to the AP+desired coffee mass within 0.01g.
At beginning of brewing, added water to as close as feasible (tho sometimes difficult on the higher brew ratio due to bloom) to the AP mass+coffee+desired brew water+~1g or so.
At press time, recorded final mass of the AP with brew mass.
Pressed the assembly, then removed the filter cap with filter, taking care to keep all remaining grounds in the AP, then weighed the:
Cap+wet filter Aeropress with spent grounds and liquid Resulting cup.
Stirred, then took a sample for cooling and checking strength. And sampled the results for taste, at native strength and diluted.
Time consuming, yes. Enlightening? Yes.
------------------------------------------ ----------------------------------------- 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
jpender Senior Member Joined: 11 Jul 2011 Posts: 428 Location: California Expertise: I like coffee
Grinder: Kyocera CM-50 Vac Pot: S/S Moka Pot Drip: Aeropress
Posted Thu May 10, 2012, 9:16am Subject: Re: Coffee Extraction Discussion, Questions for the membership:
Netphilosopher Said:
The "classic" brew charts indicate going from slightly overextracted to severely underextracted (22%ish extraction at 6g/100g to <16% extraction at 18g/100g).
Not that it matters for your purposes here but isn't your calibration weight insufficiently accurate for that class of scale?
Also worth mentioning that you'll get a bouyancy error of more than 0.01g when you weigh 40g of coffee. You could correct for this if you knew the true density of coffee (if it mattered).
Chang94598 Senior Member Joined: 24 Oct 2007 Posts: 209 Location: SF Bay Area
Posted Thu May 10, 2012, 9:57am Subject: Re: Coffee Extraction Discussion, Questions for the membership:
Extraction is not linear. On coffee particle sizes =>1mm, the center never becomes hydrated.
Imagine a single coffee ground particle. At the microscopic level, at the periphery, the coffee flavor is extracted, the fibers swell, and form a semipermeable lattice which also traps water. Solvent water then has a difficult time diffuse into the center. So technically, the periphery is over extracted, and the center is never, or under extracted. This was confirmed via electron microscopy on brewed coffee at atmospheric pressure, not espresso nor Aeropress, btw.
In my experience, with the Abid at least, even at 5 minutes, the drink does not taste too much different then 2.5 minutes.
Posted Thu May 10, 2012, 10:59am Subject: Re: Coffee Extraction Discussion, Questions for the membership:
jpender Said:
Not that it matters for your purposes here but isn't your calibration weight insufficiently accurate for that class of scale?
Also worth mentioning that you'll get a bouyancy error of more than 0.01g when you weigh 40g of coffee. You could correct for this if you knew the true density of coffee (if it mattered).
The coffee is dry when weighed in the Aeropress. Not sure why the bouancy error matters when I add water - added mass is added mass, even with air entrained in it. The foam entrained in it is negligible. As long as I don't insert anything into the brew mass that displaces the liquid (like the stirrer, even if I don't let it touch the bottom, the mass of the whole shebang increases by the displaced liquid volume at the given density).
Also, when I was doing cold brewed coffee, I did a final weigh with the mason jar sealed (and the bloom and floating grounds inside), and it weighs exactly the same 24 hr later as it did when it went into the fridge (absent the bloom and all of the grounds settled to the bottom).
Regarding the scale:
I was looking for a handful of weights to check the range and calibration of my scale(s) - and ended up with four 500g weights. When calibrated with any one of them, they all read 500.00 ± .01g, and the 200, 100, and 50g cal weights all weigh dead nuts, regardless of whether I use 500g weight A, B, C or D to cal the scale. (I'm talking about the 500X0.01g scale)
I have four of the 500g cal weights to check the linearity of my 2kg X 0.1g scale - and that scale ALSO agrees with the 500gX0.01 scale for all of the weights. And I can repeat the measurement of my cup to 0.01 gram (the AP and the cap depend on whether there's a bit of water on it or not). Yes, it's possible the weights are all off to the bottom of the tolerance, but that means 4 differently sourced 500g weights and three other cal weights would all have to be biased the same way, or I'd see it in the measurements.
(I also brought one in to work and checked it here - it also reads 499.99 to 500.00g - the .001g scale was out for cal at the time)
I think I'm "good enough". Class E1 and E2 weights at 500g are in the kilobuck range, the scale is $25 - I don't need an albatross weight if I have four 500g weights that are repeatable within the scale resolution.
------------------------------------------ ----------------------------------------- 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 10, 2012, 11:06am Subject: Re: Coffee Extraction Discussion, Questions for the membership:
Chang94598 Said:
Extraction is not linear. On coffee particle sizes =>1mm, the center never becomes hydrated.
Imagine a single coffee ground particle. At the microscopic level, at the periphery, the coffee flavor is extracted, the fibers swell, and form a semipermeable lattice which also traps water. Solvent water then has a difficult time diffuse into the center. So technically, the periphery is over extracted, and the center is never, or under extracted. This was confirmed via electron microscopy on brewed coffee at atmospheric pressure, not espresso nor Aeropress, btw.
In my experience, with the Abid at least, even at 5 minutes, the drink does not taste too much different then 2.5 minutes.
Agree. What I've found is that fine grind the extraction and taste are pretty much settled at 4-6 minutes. However, the extraction for 900micron particles and hot water may go longer than 6 minutes.
------------------------------------------ ----------------------------------------- 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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