WonderClown Senior Member Joined: 17 Apr 2007 Posts: 203 Location: NC, USA Expertise: I love coffee
Espresso: Gave away a Saeco Via Veneto... Grinder: Baratza Virtuoso, Zassenhaus Drip: Buchner funnel + vacuum... Roaster: WB Poppery I
Posted Sun Nov 1, 2009, 4:34am Subject: Re: Extraction Measurements
AndyS Said:
Gary got on board with this. Wonderclown got on board with this. Vince and James Hoffmann are on board with this. I urge you to get on board too, Alan.
For the record, I'm "on board" with the idea that the SCAA definition is ambiguous, and that it is entirely possible that the coffee world has been using the "solids in the cup/pot" interpretation rather than the "solids dissolved in brew water" interpretation. I think the reasons for this are clear given the common drip or espresso brewing methods, which are progressive extractions, where the water left in the grounds will have a different concentration than the beverage, and so calculating what was actually dissolved would be both harder and less meaningful than it is for a total immersion method like the Aeropress, or a French Press. For the total immersion methods, the "solids dissolved in brew water" makes the most sense.
But if you want your numbers to be comparable to other methods, it seems like the "solids in the cup" method is more universal. However, in my last post on this subject, I gave up on the idea of using % extraction as a way of comparing different methods. It is at best a very coarse comparison. It is useful for fine-tuning a method relative to itself or similar methods.
Posted Sun Nov 1, 2009, 2:14pm Subject: Re: Extraction Measurements
Hi All,
I spent quite a lot of time in Google Scholar seeking definitions of extraction. I found two similar to the SCAA definition, but more precisely worded. I did not find a single definition in support of AndyS's formula.
Extraction or sometimes referred to as "solubles yield" - refers to the amount of solubles extracted from the bean itself and also expressed as a percentage.
As shown in Figure 2, a 20% extraction (shown at the bottom of the chart) indicates that 20% of the soluble flavoring material was dissolved in water. For example, if 10 grams of ground coffee was used in brewing, the bean would have lost 2 grams of soluble material to water." (my emphasis)
Note that the definition refers to the amount of material dissolved in water. Not how much of that material ended up in the cup.
"The transfer of flavour components from solid to liquid form is called Extraction.
The maximum roasted coffee particles that can be dissolved in water is approximately 30%"
Note that the definition refers to the amount of material transferred to liquid and the amount that "can be dissolved in water". Not how much of that material ended up in the cup.
While the frequently cited SCAA charts appear to be based on the amount which ended up in the cup, I have not found a single definition to support that method of measurement.
Consider the following:
Let's brew two pour-overs. One with a standard cone filter, a second with a filter made from thick felt. The felt is highly permeable so the drip through times are identical. Both taste identical and measure identical strength. However the thick felt retains more liquid, and consequently less brew (and thus less solids) end up in that cup.
By the definitions which I support, the extraction percent would measure the same for both methods. By AndyS's definition, the felt filtered process would be measured as lower extraction. Yet the time and temperature of both brews is identical. How could the extraction of the felt brew be different?
Posted Sun Nov 1, 2009, 6:14pm Subject: Re: Extraction Measurements
AlanAdler Said:
Consider the following:
Let's brew two pour-overs. One with a standard cone filter, a second with a filter made from thick felt. The felt is highly permeable so the drip through times are identical. However the thick felt retains more liquid, and consequently less brew (and thus less solids) end up in that cup.
By the definitions which I support, the extraction percent would measure the same for both methods. By AndyS's definition, the felt filtered process would be measured as lower extraction. Yet the time and temperature of both brews is identical. How could the extraction of the felt brew be different?
I would consider the extractions the same. In both cases, 2 times the coffee weight would be absorbed in the grounds with the felt retaining (not absorbing) some of the brew that would normally be the cup using a paper filter.
I just don't know how you can say the water absorbed in the grounds is the same as the brew in the cup. I squeezed some drip brew grounds with my AeroPress and what came out was much more concentrated than the brew in the cup.
Posted Mon Nov 2, 2009, 7:49am Subject: Re: Extraction Measurements
Hi gt,
In this post, http://coffeegeek.com/forums/coffee/machines/448143#448143 I measured lower Brix in the retained liquid. After drip-through I lifted the paper cone out of the holder and gently squeezed a few drops on to my Brix meter. Then I applied that 1.1 Brix reading to the weight of retained liquid. This would seem to me to be the most precise of the three computations in that post and I would recommend it to anyone seeking the most accurate result.
My approximation of using the brew Brix of 1.4 yielded a closer number to the precise formula because obviously 1.4 was much closer to the actual 1.1 than zero Brix, which is effectively what AndyS advocates.
Here are those three computations again:
0.85 x Brix x (Brew wt) / (coffee wt) = 16.9% extraction This is likely the basis for the SCAA graphs.
0.85 x Brix x (Input water wt) / (coffee wt) = 19.5% extraction This is my standard formula.
0.85 x (1.4 x brew wt + 1.1 x trapped liquid wt) / (coffee wt) = 18.9% extraction This formula calculates what is removed from the 19.1 grams of coffee. This replicates the SCAA definition of extraction.
With AeroPress, the Brix of the puck is more nearly equal to the Brix in the cup. Thus the latter two results would be closer.
When I first posted my formula here, http://coffeegeek.com/forums/coffee/machines/446876#446876 I wrote, " This assumes that the brew trapped in the puck has about the same strength as the brew in your cup. I've confirmed that to be sufficiently close."
I checked that again this morning. The liquid trapped in the puck Brix = 3.3. The brew Brix = 3.8.
Extraction by my simplified formula = 21.1%. Extraction by the precise formula = 20.7%
WonderClown Senior Member Joined: 17 Apr 2007 Posts: 203 Location: NC, USA Expertise: I love coffee
Espresso: Gave away a Saeco Via Veneto... Grinder: Baratza Virtuoso, Zassenhaus Drip: Buchner funnel + vacuum... Roaster: WB Poppery I
Posted Mon Nov 2, 2009, 8:29am Subject: Re: Extraction Measurements
AlanAdler Said:
In this post, http://coffeegeek.com/forums/coffee/machines/448143#448143 I measured lower Brix in the retained liquid. After drip-through I lifted the paper cone out of the holder and gently squeezed a few drops on to my Brix meter.
IIRC, gt took the grounds themselves and pressed them in his Aeropress to extract the retained brew water for a sample. I wonder if the difference in measurements is due to the fact that he is probably getting more water from the interior of the mass of grounds, and your method gets more water from the periphery, and even from the paper filter itself, which is probably more dilute than the interior. I suppose it could also be a matter of contact time -- Alan's process was probably completed very soon after the brew cycle, whereas gt's method probably took a fair amount of time to execute, during which time the retained water was continuing to extract more solubles.
Posted Mon Nov 2, 2009, 8:59am Subject: Re: Extraction Measurements
Hi Alan,
I probably shouldn't have brought up trying to extract liquid from the grounds as it must be very method dependent. I just tried it again and I got a Brix of 2.8-2.9 which is the same as when I tried it a few days ago. The coffee in the cup in both cases was Brix 1.4-1.5 which is roughly half the grounds value.
The way I did it was this:
I used my Clever Coffee Dripper with a steep time of 3 minutes to brew 14 oz of finished brew using 16 oz of 200F water and 1 oz of coarse coffee.
After about a minute of drain through, I removed the filter with the grounds and set it on the dish drainer in the sink for about 5 minutes.
I then spooned most of the grounds into my AeroPress and squeezed out maybe a quarter teaspoon of liquid and this liquid measured 2.8-2.9 Brix using my analog refractometer.
My point is once the dripping stops, what's left is absorbed in the grounds and it's much different (stronger in my case, not as strong in your case) than the brewed coffee in the cup.
It just seems to me that the absorbed water is a result of the process and doesn't extract anything.
paulbel Senior Member Joined: 26 Apr 2008 Posts: 58 Location: Vancouver, BC, Canada Expertise: I love coffee
Espresso: aeropress Grinder: moulinex blade Drip: sometimes
Posted Mon Nov 2, 2009, 10:11am Subject: Re: Extraction Measurements
I did buy and try a Brix refractometer in my early days of using the Aeropress yet at the same time I am nothing like a coffee geek as regards measurement. (I like coffee and how it's made seem to matter.) so I'm kind of enjoying the details of the back and forth here while in kind of train-wreck awe of the little bursts of emotion that puff out of it.
Still, if people weren't really geeky about coffee we probably wouldn't have espresso machines today.
One thing I'm interested in, with the discussion of "dissolved solids" is oils. How are these things that come out of the coffee bean but are not dissolved get measured?
In particular, what happens when you use the inverted Aeropress method that presumably delivers more oils into the cup, compared with the regular method?
Posted Mon Nov 2, 2009, 3:34pm Subject: Re: Extraction Measurements
gt Said:
After about a minute of drain through, I removed the filter with the grounds and set it on the dish drainer in the sink for about 5 minutes.
I then spooned most of the grounds into my AeroPress and squeezed out maybe a quarter teaspoon of liquid and this liquid measured 2.8-2.9 Brix using my analog refractometer. Gary
It looks to me like further extraction occurred during your 5 plus minutes. Remember that I recently made some surprisingly high Brix brew at room temp in 10 minutes.
Posted Mon Nov 2, 2009, 8:58pm Subject: Re: Extraction Measurements
AlanAdler Said:
I spent quite a lot of time in Google Scholar seeking definitions of extraction. I found two similar to the SCAA definition, but more precisely worded. I did not find a single definition in support of AndyS's formula....
It's not "AndyS's formula." It's the SCAA's formula, and the SCAE's, and the SCAJ's and GHCC's, and the CBI's, and the CBC's, etc, etc, etc....
The formula and the method were developed in the 1950's by Ernest Lockhart at the Coffee Brewing Institute (later called the Coffee Brewing Center). The material isn't in Google Scholar, it's too old. If you stepped away from the computer for a moment and went to a technical library (you teach at Stanford, right?) you could locate this stuff and find out what his technique was. Then you could verify that Dr Lockhart and the coffee research groups after him base their yield calculations on solubles delivered into the cup.
Hint: when cafes send in $35, an application form, and a sample vial of brewed coffee to the SCAA for "Golden Cup" quality certification, the award is issued or rejected based on solubles yield delivered into the cup.
Hint: The Specialty Coffee Association of Europe's Gold Cup Programme works the same way, using solubles delivered into the cup. See page 10 of their powerpoint presentation, but mostly, examine their charts.
Hint: when the SCAA awarded George Howell Coffee Company's ExtractMojo "Best New Product" of their annual show, the system was based on solubles delivered into the cup. Get a copy of ExtractMojo and examine the chart.
It's not "AndyS's formula." The entire coffee world uses this formula, except for you, Alan.
-Andy S picture page: http://flickr.com/photos/andy_s/sets/
WonderClown Senior Member Joined: 17 Apr 2007 Posts: 203 Location: NC, USA Expertise: I love coffee
Espresso: Gave away a Saeco Via Veneto... Grinder: Baratza Virtuoso, Zassenhaus Drip: Buchner funnel + vacuum... Roaster: WB Poppery I
Posted Tue Nov 3, 2009, 5:31am Subject: Re: Extraction Measurements
AndyS Said:
Hint: when cafes send in $35, an application form, and a sample vial of brewed coffee to the SCAA for "Golden Cup" quality certification, the award is issued or rejected based on solubles yield delivered into the cup.
This is not, in itself, damning. The application form contains enough information that the SCAA could calculate the water retained in the grounds, using some assumptions. However, I think the SCAA's charts are enough to prove that they are, in practice, using solubles in the cup as the measure -- whether they really mean to be doing that or not, and whether they put much thought into whether that was the right way or not, or just went with what was easy.
And this is where I'm going to come to Alan's defense. His method makes more sense for total immersion, rapid filtration methods (Aeropress, French press) than the solubles-in-the-cup method. The latter makes more sense (or rather, is simply easier) for progressive extraction methods (drip, espresso). So which method to use depends on what your goal is. If you want to quantitatively compare Aeropress brewing to drip brewing, well you ought to be using the same method, whichever way you do that. Since Alan's method is difficult to execute reliably with drip brewing, that would lead me to say you would be better off with the SCAA method. But I don't think it's particularly meaningful anyway, because the quantitative comparison is a false comparison -- the methods are very different, and there is good reason to think that there is a different extraction sweet spot with the two different methods.
If two Aeropress users want to compare notes, I would advocate Alan's method, with the caveat that you may achieve identical extraction numbers with very different results. For example, you can get 20% extraction with 175F water or with 205F water, by adjusting grind, contact time, and/or water:coffee ratio. I suspect the coffee will taste quite different, even at the same extraction.
I think the most meaningful thing to calibrate to when comparing brewing methods is TDS of the coffee as consumed -- if I get both cups to 1.25% TDS (diluting as necessary) and the same temperature and taste a difference, I know the difference comes from the brewing methods, not just from one cup being weaker than the other. At that point, qualitative taste rules, not the numbers.
It's not "AndyS's formula." The entire coffee world uses this formula, except for you, Alan.
Which is only relevant when he is publishing numbers intended to be compared to SCAA numbers (which he has often done). Otherwise, it only matters if you suffer from Authoritarian Personality Disorder and cannot tolerate dissent. It says nothing about what the "right" way to do it is. But I agree, Alan should be careful when discussing the Golden Cup standards with respect to the Aeropress.
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