Posted Fri May 11, 2012, 11:54am Subject: Re: Coffee Extraction Discussion, Questions for the membership:
jpender Said:
By the way, I'm looking for an inexpensive scale. I read a comment on Amazon.com about the one you purchased. The person was claiming that it locks into 100g increments. I'm familiar with the annoying but common tactic of reporting zero when small masses (presumed drift) are added after the tare is used. But does your scale also do this at 100g increments as the reviewer claimed? I'd like to avoid that "feature" if possible.
I was also concerned about the commenter's observation, but honestly I don't think I see that happening. If I have the scale stabilized, I have to make sure any additional mass takes it out of the stabilized zone (i.e. if you drop a few grains of coffee onto something that reads 100.00, you should tap the scale and let it re-stabilize, and usually it will register 0.01 changes). Same thing if you remove the thing being measured and re-place it.
One thing I've noticed with all of these scales (the 2kgX0.1g and the 500gX0.01g) is that they can be sensitive to static and also thermal changes.
I need to do a quick damp-dry wipe on the scale pad and the AeroPress, or I can see a few hundredths of a gram change as the AP approaches the scale pad. This is static that goes away with a quick wipe and re-tare. Also once the press is on, the static of your approaching hand can be registered. It took me a while to figure out what was happening.
Thermal: If you put a hot cup of coffee on the pad, the scale will stabilize and then after a few seconds will begin to drift (not much more than a tenth of a gram), and then the tare will be off by about 0.1g (a bit more on the 2kg scale). Have a nice insulating pad as a tare for coffee cups or something to reduce heat transfer to the scale pad.
But still a heck of a deal for $20 or so...
------------------------------------------ ----------------------------------------- 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: 408 Location: California Expertise: I like coffee
Grinder: Kyocera CM-50 Vac Pot: S/S Moka Pot Drip: Aeropress
Posted Fri May 11, 2012, 12:56pm Subject: Re: Coffee Extraction Discussion, Questions for the membership:
Netphilosopher Said:
I was also concerned about the commenter's observation, but honestly I don't think I see that happening. If I have the scale stabilized, I have to make sure any additional mass takes it out of the stabilized zone (i.e. if you drop a few grains of coffee onto something that reads 100.00, you should tap the scale and let it re-stabilize, and usually it will register 0.01 changes). Same thing if you remove the thing being measured and re-place it.
No, not just at the 100.00. It's anytime it's stabilized no matter what weight it is on it. When a scale like that stabilizes, usually (as explained to me by a friend of mine in instrumentation) the scale is sampling and averaging - when the reading variation drops below a certain threshold for a certain time (all control algorithm based) it considers it's stabilized and reports the value - and the sampling rate drops. If one of the slower sample rates goes out of the range, it generally re-samples and re-reports after it re-stabilizes.
When you take a scale and change the weight on it by near the resolution, it doesn't consider the slight wiggle of the strain gage enough to worry about. Sometimes I just puff at it and that's enough.
I am able to fit the AeroPress on it without an issue. I do like the small size, but I still pull out my bigger scale just as a cross check or for convenience or measuring larger than 500g stuff. Like I couldn't do most of my beans for roasting on the little one.
I figgered for $22... <shrug> been happy with it so far.
------------------------------------------ ----------------------------------------- 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 Fri May 11, 2012, 7:07pm Subject: Re: Coffee Extraction Discussion, Questions for the membership:
Netphilosopher Said:
First - the brew charts are indeed predictor charts (hence the term "control" charts), and based on an assumed "absorption". Change the absorption and you change the brew charts.
Any part on the brew chart consists of 4 parameters in a closed solution where the 4th parameter is hidden and assumed to be the same for all brew methods.
(1) Sure, a brewing chart is a rough "predictor" of how much beverage you will end up with, given a measured dose, a measured amount of brew water, and a decent guess at the absorption factor. (2) But a brewing chart is a poor "predictor" of what the beverage strength and extraction yield will be, since changing the brew ratio will change the amount of solids that are extracted from the dry coffee. (3) I agree with jpender that your equation Extraction = Strength * ((1/Brew Ratio) - Absorption) is only approximately correct, since it ignores the extracted solids as part of the beverage mass. The fact that it matches up well with a 50 year old chart doesn't mean it's correct; we know the creators of those charts made errors and/or omissions.
Posted Sat May 12, 2012, 2:06pm Subject: Re: Coffee Extraction Discussion, Questions for the membership:
andys Said:
(1) Sure, a brewing chart is a rough "predictor" of how much beverage you will end up with, given a measured dose, a measured amount of brew water, and a decent guess at the absorption factor...
(2) But a brewing chart is a poor "predictor" of what the beverage strength and extraction yield will be, since changing the brew ratio will change the amount of solids that are extracted from the dry coffee.
I'm not sure I agree with this. Lockhart's studies using the dehydration method of extraction (basically the backbone of extraction definition) used FILTERED coffee. The extraction is only the dissolved portion, just like the VSTcr - which is also correlated to only the dissolved portion and how they change the nD of the coffee beverage. Any studies based on the VSTcr will be in line with this.
Unless I misunderstand your point.
When I present an amount of dry coffee, a produced beverage at a given strength, and you plug this into any formula to determine "extraction", the result is basically straightforward math:
Coffee Beverage X %TDS = TDS TDS/Dry Coffee = Extraction.
This works because the studies on strength, extraction and brew ratio were all done with this definition in mind. The "brew control charts" were the idea that since you can alter the brewing parameters for a given brew ratio, you can change whether the coffee is underdeveloped, over-developed, or in the middle of the "sweet spot".
My thinking is that any time I can reproduce a brew with the same method and the resulting beverage amount and strength are repeatable, I have a predictable system.
andys Said:
(3) I agree with jpender that your equation Extraction = Strength * ((1/Brew Ratio) - Absorption) is only approximately correct, since it ignores the extracted solids as part of the beverage mass. The fact that it matches up well with a 50 year old chart doesn't mean it's correct; we know the creators of those charts made errors and/or omissions.
Again, I'm interpreting your term "extracted solids" as the solids that have not been dissolved but make it into the beverage. The VSTcr and the old studies both eliminate these solids as part of the result. The standard protocol for dehydration is for filtration of the sample prior to dehydration (specifically to remove these solids as part of the measurement of extraction), and the VSTcr has been correlated to the dehydration method this same protocol.
The Brewing Control Charts are based on a term called absorption because to use a brew ratio to control the end strength makes sense - and you need a reliable way to predict the end amount of coffee produced, so you can determine the extraction based on the TDS in the end result. It isn't something I made up - Lockhart et.al. did.
The premise is:
Coffee Produced = Brew Water - (Absorption X Dry Coffee) (corrected 5/14/12)
This predicts the coffee produced. From the coffee produced, you can measure the strength (aka %TDS).
(Coffee Produced X %TDS)/Dry Coffee = extraction
When you produce espresso, you have your espresso produced multiplied by your %TDS from the VSTcr, and divided by the coffee you used to make it to obtain extraction. There is no absorption, because you don't know your brew water - you simply control how much espresso you make when you pull your shot. Conventional brewing of coffee we don't get that luxury - if we want to end up with some amount of coffee we have to control these parameters before we make the coffee.
All I did was normalize the equations into brew ratio, but the equations are all standard coffee extraction theory.
------------------------------------------ ----------------------------------------- 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
I believe you have a typo there, and you meant to say:
Coffee Produced = Brew Water - (Absorption X Dry Coffee)
But since you haven't defined "Absorption" (or at least I don't see where you have), the equation is ambiguous.
It appears you are defining Absorption as: ((weight of wet grounds/weight of dry grounds) - 1)
A more intuitive (and perhaps more accurate) definition of Absorption might be: (amount of brew water absorbed by the grounds/weight of dry grounds)
Here's an illustration of the difference with numbers: say we start with 10 grams of dry grounds. After extraction our wet grounds weigh 30 grams, and our extraction yield is 20%.
Using your definition, Absorption = (30/10) - 1 = 2
Using the second definition, we take into account that 2 grams of soluble solids have been removed from the grounds. Absorption = (30-8)/10 = 2.2
The second definition is the one that ExtractMoJo software is using. Tellingly, it is referred to as a "water lost" ratio (as in: brew water absorbed by the grounds, "lost" to the beverage).
I'm not saying your definition is "wrong." By choosing an appropriate absorption number, you can make the figures come out OK. But since the whole point of extraction theory is to focus on how much material is removed from the dry coffee, your definition seems like an inappropriate oversimplification to me. I haven't worked it all through, but I believe it creates some problems down the line.
Netphilosopher Said:
All I did was normalize the equations into brew ratio, but the equations are all standard coffee extraction theory.
Perhaps you'll agree there is no "standard coffee extraction theory." We are learning that Lockhart did brilliant work; but he did make mistakes, and it's up to us to identify and correct them.
Posted Mon May 14, 2012, 4:38am Subject: Re: Coffee Extraction Discussion, Questions for the membership:
Corrections made
------------------------------------------ ----------------------------------------- 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
Yep you are correct, and corrections made above. Thanks for the catch.
andys Said:
But since you haven't defined "Absorption" (or at least I don't see where you have), the equation is ambiguous.
It appears you are defining Absorption as: ((weight of wet grounds/weight of dry grounds) - 1)
A more intuitive (and perhaps more accurate) definition of Absorption might be: (amount of brew water absorbed by the grounds/weight of dry grounds)
Here's an illustration of the difference with numbers: say we start with 10 grams of dry grounds. After extraction our wet grounds weigh 30 grams, and our extraction yield is 20%.
Using your definition, Absorption = (30/10) - 1 = 2
Using the second definition, we take into account that 2 grams of soluble solids have been removed from the grounds. Absorption = (30-8)/10 = 2.2
The second definition is the one that ExtractMoJo software is using. Tellingly, it is referred to as a "water lost" ratio (as in: brew water absorbed by the grounds, "lost" to the beverage).
I'm not saying your definition is "wrong." By choosing an appropriate absorption number, you can make the figures come out OK. But since the whole point of extraction theory is to focus on how much material is removed from the dry coffee, your definition seems like an inappropriate oversimplification to me. I haven't worked it all through, but I believe it creates some problems down the line.
Perhaps you'll agree there is no "standard coffee extraction theory." We are learning that Lockhart did brilliant work; but he did make mistakes, and it's up to us to identify and correct them.
The definition of absorption wasn't up to me - I am using what was available regarding the way the brew chart was defined.
Absorption is the concept of how much is captured and doesn't end up in the cup - as a ratio of the coffee mass. You're right that a more intuitive way would be to re-define it, but I see the easier way to look at it. It helps the algebra. Rather than creating problems, it actually makes it cleaner - depending on the assumptions you're willing to make.
The unknown here is the strength of the liquid in the spent grounds - and whether it should be counted as extraction or not. The standard answer is "no". Extraction is pretty simple: (yield beverage X strength )/dry coffee.
That's why the absorption, for the most part, doesn't technically matter - it only matters if you care about the brew ratio and the ability of this parameter to control part of the end strength.
Let's work it backward: Say I want 700g of coffee at 1.25% strength. I also want 20% extraction. How much coffee do I use?
That's simple: (700X0.125)/0.20 = 43.75g of coffee.
Now, how much WATER do I use in my BCM-4C?
Tricky. I want 691.25g of water in the end, so I know I need at least that much in the reservoir. I'll probably lose about 15g in the brew process, so I'll add that (706.25). But I need to know how much to add in the reservoir that will end up stuck in the exchange of solubles, solutes and solutions in the spent grounds - that's EXACTLY where the absorption comes in. If I know it's 2.06, then I just add 2.06Xdry coffee mass to the brew water and I'm all set - 796.375 to 43.75g of coffee (or the familiar standard of 5.5%).
Without that absorption, or with a more complicated absorption, it gets really messy. I see exactly why they defined it that way - it works (most of the time) with basket brewers like the Bunn. If you're thinking in mass but your brew water is volume, it gets thrown off a bit. Cone-type filters have a higher percolation pressure gradient, so they will trend lower (the last half dozen in my little BCM-4C were right around 1.85).
I wanted to start with reconstitution of the old standard brew chart, and go from there. The interesting thing is that if I adjust the chart with a mass-based brew ratio, and then adjust the "absorption" to what my brewer actually does - I get a pretty decent approximation of the extraction in taste. Surprisingly good, in fact. Brews that calculate >22.5% extraction taste like it, brews that are between 18% and 19.5% taste pretty good. Unfortunately with a 6min brew cycle, it's more difficult to get an underextracted brew.
I'm trying to reconcile this with how the Aeropress brews.
Again, I didn't come up with the definitions, I'm just understanding and utilizing them. I didn't see the need to redefine "absorption", because that's the basis of the brew control charts (which doesn't apply to espresso, since you don't know the brew ratio). Absorption is the increase in the grounds mass after brewing as a ratio of the dry coffee mass. It has no technical upper limit, and it has a lower limit of -Extraction (that's negative extraction).
In fact, if you plug in -Extraction for absorption, and add it to the dry coffee mass, you'll yield the expected dry SPENT coffee mass. I think that's part of the reason the definition works.
------------------------------------------ ----------------------------------------- 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 Mon May 14, 2012, 10:01am Subject: Re: Coffee Extraction Discussion, Questions for the membership:
Also, if you think of the system in terms of "espresso brew ratio" (i.e. the ratio of coffee mass used to produce a given mass of espresso), the whole thing is very simple:
Extraction = Strength / EBR
So, if you use 7 grams of coffee to produce 28g shot, the EBR is 25%. If the strength is 5%, the extraction is .05/.25 or 20%.
Given a desired strength and extraction, you have how much you need to think about producing, if you define the coffee amount:
19% extraction at 10% strength, you want to use 15g of coffee:
EBR = Strength/Extraction, .10/.19 = 52.6% EBR,
15g/.526 = 28.5g shot should be your espresso target. The whole concept of "absorption" goes out the window with regard to 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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