Posted Thu Jun 30, 2011, 5:38am Subject: Musings On Coffee Extraction, and measuring it:
So, I have gotten a couple of emails about how I calculate coffee extraction, and one of them has given me pause to think. Any experts out there that could help clarify.
Some people use a refractometer and get the %TDS (or strength) of the brewed beverage. Knowing the mass of the beverage, the extracted solids can be determined simply, and divided by the mass of the coffee used to make it to establish extraction.
Example: 8g coffee, espresso produced is 32g at 5% strength as accurately measured on a refractometer calibrated for coffee. Extracted coffee is 1.8g of TDS (5% of 32g), extraction is 1.8g÷8g = 20%.
simple right?
If you dry the puck and weigh it, not surprisingly it will weigh 6.4g, or 80% of what it originally weighed. If you evaporate the shot, you end up with 1.8g of very thick solids left behind (strangely, not all of the evaporated solids are strictly "solid", think partly powder and partly something about 20X as thick as molasses but not strictly liquid and not strictly a powder).
Using an espresso machine, we don't really know how much water was used to press it, although we could weigh wet pucks. Usually they weigh about 22± grams.
Or you can brew coffee, then evaporate the results and measure the mass of coffee left behind in both the puck and the beverage itself.
Since I mostly brew using an Aeropress or Press Pot, I have spent significant time measuring extraction and tracking mass of coffee, water, and evaporation results through the brewing process. One example:
22.5g coffee 125g brew water
After brewing:
100g coffee produced at 4.5% strength (evaporating this 100g leaves behind 4.5g of coffee solids)
the wet puck weighs about 47.5g (give or take, usually a tenth or two of wetness is left behind in the paper disc filter). When dried, it weighs 18g, so the wet puck consisted of 29.5g of water with 18g of coffee solids when it was wet.
I've considered that this is a near-perfect example of a 20% extraction, and this seems to be in line with my taste preference. When this is above 22%, the coffee takes on the bitterness of roast byproducts, and 17% and below it loses bitterness but also loses brightness and acidity and varietal flavor.
BUT...
It was brought to my attention that when brewing, just before separating the grounds, I have a slurry consisting of 22.5g of coffee and 125g of water (total of 147.5g) which means if properly extracted, the solution made by ALL of the water contains dissolved solids that end up stuck in the puck.
In my example above, it really means: 22.5g coffee with 125g brew water
After brewing: 100g of 4.5% strength beverage produced (95.5g water + 4.5g dissolved coffee solids) Puck consists of 18g coffee + 29.5g of water as a SOLVENT - it really consists of 30.9g of 4.5% strength coffee (29.5g water + 1.4g dissolved coffee solids), and only 16.6g of undissolved coffee solids.
In other words, if I could get all of the "coffee" out of the puck, I'd be left with only 16.6 g of undissolved solids and a total of 130.9g of 4.5% strength coffee consisting of my 125g of water + 5.9g of TDS.
This would imply what tastes very good is in fact a ridiculously overextracted 26.2% extraction.
However, if you're trying to justify an Aeropress "recommended" brew, this makes it magically "perfectly" extracted:
My experiment using Aeropress recommended 175°F water, 2 "scoops" beans ground to between drip and espresso, filled to "2", 10seconds... the works, except I weighed everything: 27.2g coffee 99.7g brew water
Produced 73.6g of concentrated coffee with little varietal flavor but very smooth (no bitterness) as tasted on a "sister" brew (same paramters, weights within 0.5g). Slightly sour, no real acidity, no acid or fruit notes on a bean which should have had some.
Evaporated, it contained 4.3g of coffee solids, meaning the resulting strength was 5.85%.
The puck weighed 52.7g wet, and 22.9g dried.
I figured the extraction at 4.3÷27.2 or only 15.8% extraction - and had guessed it underextracted on the sister taste brew.
BUT, if you employ the reasoning that the coffee stuck in the puck was same strength as the brewed coffee, the wet puck actually consisted of 31.65g of 5.85% strength coffee (29.8g water + 1.85g dissolved solids) and 21.05g of undissolved coffee solids. This implies an extraction of a magic 22.6% ((4.3g+1.85g)÷27.2g = 22.6% - technically OVER extracted if you use the SCAA guidelines of between 18% and 22%). There is absolutely no way the Aeropress overextracts when used per instructions, based on my experience.
There is no way this can be right, but it also implies that if you can press more out of the puck you might be able to change the "measured" extraction. Most of the time, it seems the puck has an absorption of 1.08 to as high as 2.0 on some extraction methods (the amount of water in the puck divided by the original mass of the coffee). It seems I cannot get more out of the wet puck by pressing it harder (maybe a couple tenths of a gram) - just can't be done. I've also confirmed these types of measurements using drip pots, pourovers, etc., and when someone makes a "properly" extracted coffee that tastes correct, the extraction always seems to be between 17.9% and 21.7% using my original evaporation method - but would be well over 23 or 24% if you use the "coffee trapped in the grounds" thinking.
Thoughts? I think it's as simple as if you take the brewed coffee, evaporate it and weigh the solids left behind, these solids divided by the original coffee IS the extraction. If you use this method, you find out that cold brew coffee and Aeropress using low temperature and short contact time consistently underextract, and most of the other methods done according to custom seem to extract in the "sweet spot".
I also think that because it seems nearly impossible to get the rest of the "coffee" out of the puck, it's more likely that the "absorption" is really just water that's stuck in the cellulose and undissolved parts of the coffee, and may not in fact be coffee at all - for all practical purposes you can't get this out so it should never be counted as part of the extracted coffee.
------------------------------------------ ----------------------------------------- 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 Jun 30, 2011, 6:25am Subject: Re: Musings On Coffee Extraction, and measuring it:
22.5g coffee to 125g water = 180g/L. That's triple the SCAA recommended brew ratio. So, my question would be, how does grind impact all this? What does your stated brew look like in terms of grind and contact time?
germantownrob Senior Member Joined: 2 Dec 2007 Posts: 2,038 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 Thu Jun 30, 2011, 7:08am Subject: Re: Musings On Coffee Extraction, and measuring it:
Netphilosopher Said:
So, I have gotten a couple of emails about how I calculate coffee extraction, and one of them has given me pause to think. Any experts out there that could help clarify.
after reading through what andy has to say in that thread I have questioned just how accurate your results are however I still like reading what you have to report because I know you are having fun doing your "geek" thing and it is interesting to follow your point of view.
Edit: from a mainly espresso drinkers perspective different grind and dose will greatly change the outcome of taste (temp of brew water and amount as well). Click Here (www.home-barista.com) These small changes have a drastic effect on the taste of the espresso and in the end that is what is important to me, I am certain the TDS changes as well but has little bearing on what a person likes in their cup.
Now I have wondered how these changes will effect other brew methods and to what degree "Has anyone experimented with up dosing and grind size for drip or french?" I realize the changes in grind size and dose would have to be more extreme for other brew methods but not sure if the effects on taste would have the similar results.
Posted Thu Jun 30, 2011, 8:12am Subject: Re: Musings On Coffee Extraction, and measuring it:
I really admire what you're doing. After all, we are Coffee Geeks.
At the same time, I wonder if there is a less complex model that connects flavor to brewing conditions.
Indeed, the word 'flavor' contains families of lumped variables, such as ...all the variables in Sweet Maria's cupping wheel'... plus ... all the variables in 'roast degree'... plus ...all the variables in 'brewing system'.
I am NOT being critical. Here I am, finishing a mug of Sumatra Mandheling, evenly roasted to FC, ground at 16 on my Maestro Plus, brewed in an Aeropress at 190F for 1:30 min. And it's just so good. And here I am wondering: "What did I do right?"
Posted Thu Jun 30, 2011, 8:15am Subject: Re: Musings On Coffee Extraction, and measuring it:
SteveRhinehart Said:
22.5g coffee to 125g water = 180g/L. That's triple the SCAA recommended brew ratio. So, my question would be, how does grind impact all this? What does your stated brew look like in terms of grind and contact time?
The SCAA guidelines are made to produce a beverage between 1.15% and 1.35% strength - the percentage (by mass) of total dissolved solids in the total mass of the resulting coffee. This should never be confused for extraction, which is the mass extracted into the coffee as a percentage of the coffee used to make it.
A straight up cup of coffee brewed to normal target strength of 1.25% would use a brew ratio of 5.5 or 5.6%. I can easily do this in an Aeropress, though it is difficult to produce much more than a couple hundred grams due to fresh coffee ground bloom.
Grind affects extraction to the extent that it is matched to the contact time AT TEMPERATURE. Even the finest grind cold brewed cannot do much more than 17% extraction.
My specific setup is a grind just a bit finer than drip, approximately the same as setting 6 on Zingerman's coffee house Ditting, and magnified appearance roughly equal to a Keruig K-cup or Flavia single serve cup (both methods slightly underextract, and compensate for coffee flavor by using darker roasts). Contact time is 1 min 30 sec in an inverted Aeropress, as quick as possible press (usually about 20-30 seconds).
Properly extracted concentrated coffee can be created up to about 5-6% strength - much more than that and the extraction seems to be inhibited, either by the lack of energy (temperature) because of the ambient temp of the grounds lowering the temperature of the slurry, or because the concentration of dissolved solids impairs further extraction. This concentrated coffee, when diluted to 1.25% strength, is indistinguishable from coffee brewed using SCAA brew ratio with proper extraction.
germantownrob Said:
andys is the one person on this subject I have come to trust, don't be fooled by his profile saying he is 99 and that he is just starting, LOL.
after reading through what andy has to say in that thread I have questioned just how accurate your results are however I still like reading what you have to report because I know you are having fun doing your "geek" thing and it is interesting to follow your point of view.
Edit: from a mainly espresso drinkers perspective different grind and dose will greatly change the outcome of taste (temp of brew water and amount as well). Click Here (www.home-barista.com) These small changes have a drastic effect on the taste of the espresso and in the end that is what is important to me, I am certain the TDS changes as well but has little bearing on what a person likes in their cup.
Now I have wondered how these changes will effect other brew methods and to what degree "Has anyone experimented with up dosing and grind size for drip or french?" I realize the changes in grind size and dose would have to be more extreme for other brew methods but not sure if the effects on taste would have the similar results.
As for the accuracy, when I weigh a sample (say a 68.2g "double espresso" shot from *$s) of espresso, then dehydrate it in an oven at 215°F and obtain 3.4g of coffee solids, there is little doubt the strength of that beverage is right about 5% (3.4g÷68.2g = 0.04985 or 5%). I weigh the dehydrating bowl both before and after dehydration and cleaning to make sure the scale is right. Incidentally, this same sample showed the °Brix at 6%, implying (0.85 anectdotal fudge factor applied) an approximate strength of 5.1%. The refractometer is made for sugar and has a very coarse scale.
Measuring strength, evaporation method of coffee is about as accurate as it gets. It's just time consuming. I don't think this is in dispute with Andys' comments - it was more about the effort I was putting forth and how much easier it would be to use an ExtractMojo for instant feedback on the resulting strength. By the way, his extraction math works out well using his example Espresso Brew Ratio - using what I think should be used for calculating it.
When it comes to extraction methods, extraction is extraction, and the flavor can be changed by the presence or absence of oils and fines. Press pot will have more perceived body because of oils and fines. Up-dosing press pot works, actually pretty well. I have created very good 3.5% strength coffee with my Bodum - because extraction is extraction. We're all just trying to get those special 20% of the solids into water.
------------------------------------------ ----------------------------------------- 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 Jun 30, 2011, 8:16am Subject: Re: Musings On Coffee Extraction, and measuring it:
JKalpin Said:
... I am NOT being critical. Here I am, finishing a mug of Sumatra Mandheling, evenly roasted to FC, ground at 16 on my Maestro Plus, brewed in an Aeropress at 190F for 1:30 min. And it's just so good. And here I am wondering: "What did I do right?"
You didn't use 175°F water and your grind level was fine enough to make 1:30 work - good job!
(I'm finding the critical temperature is breakpointing right around 185°-190°F)
------------------------------------------ ----------------------------------------- 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: 2,038 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 Thu Jun 30, 2011, 9:25am Subject: Re: Musings On Coffee Extraction, and measuring it:
Well I did see andys mention dehydrated grinds will quickly absorb moisture out of the air so relative humidity plays a factor at the time of testing. Scales are not all created equal and taste is subjective especially when not blind tasting. Not sure if moisture retained in the bean after roasting plays into any of this but it does change the percentage lost after roasting depending on what is done during the drying phase of a roast by as much as 1-4%. I admit I could be completely wrong in my assumption that pre brew weight and the varying moisture retention of that particular roast could have effect on your results.
Extraction is extraction, ok, but a 14g, 1.5oz shot of espresso brewed in 25 sec is going to taste different then an 18g, 1.5 oz shot brewed in 25 sec as will a 18g, 2oz brewed in 25 sec, and so on, each of these shots will be extracting differently and there is no right or wrong to them it is just taste.
Sorry for this part because it is a critical critique of what you do when people respond to you. You gloss over what they say and respond with a ton of facts that say you are correct. Even in this thread where you start by asking a question about your methods and results it seems you are really saying everybody else is wrong and you are right. Your back and forth with andys had much more in them then him just agreeing with you and I believe with your true coffee geekness it would be a shame not to pursue conversations with him where you really listen to what he has to say. I have a ton of respect for you and your experiments and do love that you share them with us so I hope you don't get offended by my criticism.
Posted Thu Jun 30, 2011, 10:46am Subject: Re: Musings On Coffee Extraction, and measuring it:
germantownrob Said:
Well I did see andys mention dehydrated grinds will quickly absorb moisture out of the air so relative humidity plays a factor at the time of testing. Scales are not all created equal and taste is subjective especially when not blind tasting. Not sure if moisture retained in the bean after roasting plays into any of this but it does change the percentage lost after roasting depending on what is done during the drying phase of a roast by as much as 1-4%. I admit I could be completely wrong in my assumption that pre brew weight and the varying moisture retention of that particular roast could have effect on your results.
Extraction is extraction, ok, but a 14g, 1.5oz shot of espresso brewed in 25 sec is going to taste different then an 18g, 1.5 oz shot brewed in 25 sec as will a 18g, 2oz brewed in 25 sec, and so on, each of these shots will be extracting differently and there is no right or wrong to them it is just taste.
Sorry for this part because it is a critical critique of what you do when people respond to you. You gloss over what they say and respond with a ton of facts that say you are correct. Even in this thread where you start by asking a question about your methods and results it seems you are really saying everybody else is wrong and you are right. Your back and forth with andys had much more in them then him just agreeing with you and I believe with your true coffee geekness it would be a shame not to pursue conversations with him where you really listen to what he has to say. I have a ton of respect for you and your experiments and do love that you share them with us so I hope you don't get offended by my criticism.
thanks for the feedback, and nah, I don't get offended easily, so don't worry about it. It's all coffee, anyways. This is just stuff I'm figuring out about coffee, I'm fairly new, and so expect questioning on my methods and accuracy. Call it hobby experimentation on a budget (ergo the reason I don't own a Ditting or the new Breville, nor do I own an ExtractMojo).
I was concerned about both pre-brewing moisture content and post-drying moisture absorption, that's exactly why I checked this phenomenon.
Pre-brewing, I did try drying freshly roasted grounds, but they only lost about 0.1g in an hour (in 30g), so I considered that newly roasted and properly (dry) stored are sufficiently dry, having had most of the moisture removed by roasting anyway. It's an excellent way to end up with a flat cup of coffee, though. :D
Post brewing, I have found the dried grounds gain 0.1g in the first 10 minutes if the relative humidity is >50% ambient, a bit longer in the winter and the ambient humidity is lower. They seem to gain about 0.5g in a couple of hours if left sitting out and the relative humidity is high. I have not personally seen the rapid gain of significant weight that andys mentioned, and the other part is being able to consistently duplicate the results - which I have.
The dehydrated solids from coffee (the beverage) do not gain or lose moisture over time (checked over 12 hours). That stuff is dry and remains dry.
This stuff isn't "magic", this is just good old basic kitchen science. There's nothing magical about a coffee refractometer, the Aeropress, a vacuum brewer, a chemix, or even an espresso machine, any more than there's anything magical about road racing a car and winning a race. It's all a learned craft. In many craft, there are rules of thumb - they are nothing more than guidelines. Reading many of the posts in the past here on CG, it seemed like there is this thinking that coffee is magical, or you need complicated mass spectrometers, refractometers, and arcane hi technology methods to understand brewing coffee, otherwise you must follow rules of thumb.
Deeper understanding of the nature of coffee doesn't require much more than a few simple instruments, your taste buds, a stable methodology, and some time. And maybe a bit of curiosity. I don't post this stuff to say "i'm right and everyone else is wrong", I post results as a scientist - so people, if so inclined, can duplicate them. I post them in hopes that I encourage someone else to try the stuff that I have - maybe their different results might further my understanding, or give me insight to what might be wrong.
As an example, after Andys' comments about moisture gain of dried grounds, I went back and re-checked to make sure nothing had changed. It had, but only by a bit. Being later in the year, the +0.1g time of ~18g of coffee was shorter, and because I knew the relative humidity I am fairly sure I knew why. I also understood that the difference may have been the different drying temperatures - Andys' attempts to dry grounds was done much higher than I was doing, maybe this completely overdries the grounds? I don't know, but listening and reading responses helps keep me sharp.
I feel I do myself a disservice if I did these hobby experiments in a vaccum and never got feedback. I only post a very small amount of what I actually do - people are bored enough already of hearing me do weird things like making a half dozen cold brew coffee single servings to check extraction... LOL
Maybe people get something out of my posts, maybe not, but it also increases input through other channels as well, suggestions or further questions. I get something out of it, so I guess I'll continue until I get bored or until I get banned for being a post whore ;-)
I certainly hope that nobody ever takes offence at any of my replies - they aren't meant to be offensive, just thorough.
(by the way, I got a chance to review a couple of comments, and essentially the accepted way of defining extraction seems to be exactly what I thought - the coffee solids in the cup as a percentage of the grounds used to make it is the definition of extraction)
------------------------------------------ ----------------------------------------- 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: 2,038 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 Thu Jun 30, 2011, 11:06am Subject: Re: Musings On Coffee Extraction, and measuring it:
Netphilosopher Said:
thanks for the feedback, and nah, I don't get offended easily, so don't worry about it. It's all coffee, anyways. This is just stuff I'm figuring out about coffee, I'm fairly new, and so expect questioning on my methods and accuracy. Call it hobby experimentation on a budget (ergo the reason I don't own a Ditting or the new Breville, nor do I own an ExtractMojo).
Steve, Good. I actually logged on to erase my post, I feel much better about encouraging people about coffee then criticizing their ways. Keep it up and keep learning, after 5 years of roasting very seriously (might be getting close to 1000lbs of roasted beans) I am just a babe in the woods and don't feel like there is an end, that is why I love this hobby.
Posted Thu Jun 30, 2011, 12:00pm Subject: Re: Musings On Coffee Extraction, and measuring it:
germantownrob Said:
Steve, Good. I actually logged on to erase my post, I feel much better about encouraging people about coffee then criticizing their ways. Keep it up and keep learning, after 5 years of roasting very seriously (might be getting close to 1000lbs of roasted beans) I am just a babe in the woods and don't feel like there is an end, that is why I love this hobby.
np - I've been around and/or administrating or advising on forums for many years. I know how sometimes nuances and non-verbal communication do not come through on a text only post. 'sall good! <thumbs up> (need some other emoticons readily available on this forum - LOL)
------------------------------------------ ----------------------------------------- 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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