I'm working on best way to summarize and show the data - and will probably start a new thread when I do.
------------------------------------------ ----------------------------------------- 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, 12:46pm Subject: Re: Coffee Extraction Discussion, Questions for the membership:
Also, in looking at the old development and coffee testing back in the 50s and 60s (the basic development of the brew chart, by Lockhart and others), I noticed that in every case they keep talking grams of coffee to oz of water.
The weird thing is that oz (a volume) of water is different depending on temperature. (thanks to jpender, you got me thinking about it!!!) It appears that it's probable the brew charts were developed using HOT water volume, and knowing they would have been as precise as possible and no access to instant-read digital scales like we have today, they would have been fanatical about measuring exact volume.
Fast forward 60 years, and we now have unbelievably great measurement devices for mass. The most uncertainty is actually volume. The clues come from old army studies on coffee (also where Lockhart was involved) and a passage in one of them struck a chord in the back of my mind: "it is much easier and quicker to obtain a consistent and accurate reading with volumes and hot liquids than it is with measuring weight..."
And if all you had was one of those precision balance scales, this would be VERY true - they are a true pain to use, and when trying to get the brew water temperature as close to a specific setting as possible, you can't fart around with a balance scale trying to get it to be within a tenth of an oz - much easier to have a reference volume and be done with it.
The density of water is 1.0 at 4°C. At brewing temperatures, this changes fairly rapidly but is approximately 0.9625 at 94°C - or about 3.75% less mass than the volume in ml would indicate.
I've always used these as fairly interchangeable (g of water and ml of water), but turns out that changing the brew ratio by 3.75% re-jiggers the brew chart. A lot.
If you're using 55g per 1 liter (5.5% brew ratio), at 20% extraction your expected strength is 1.24%. You could conversely state this as if you use this brew ratio and count 1 liter as 1000g of water, and achieve a strength of 1.24%, then your extraction is 20%.
Note: Some people define brew ratio as the inverse of what I show to make it a whole number - 5.5% (aka 0.055) coffee : Water is the inverse of 18.18 water : coffee
The absorption = 2.068 by historical precedent. Most brew charts that you see have this assumption, with the exception of the modern Bunn brew control chart available on their website, where their absorption has a variance built into it based on brew ratio and extraction).
Inverting this, if you know your brew ratio, and you know your strength, then you can see where you extracted on the brew chart:
If you use 55g/1 liter of hot water, and achieve 1.24% strength, your calculated extraction is 20% on the classic brew chart. This is actually the same thing as using 55g/962.5g of hot water.
BUT if you use 55g / 1000g of hot water and achieve 1.24% strength, your calculated extraction is only 19.2% (because you achieved the same strength but used a higher brew ratio relative to volume to get there). On the chart, it's the same thing as using a brew ratio of 57g/1 liter and achieved 1.24% strength.,
Conversely, if you do everything right to brew the coffee to reach 20% extraction (assuming that's your taste target), and you back figure your extraction with 55g / 1000g of hot water, and you actually DID reach 20% extraction, your strength will be a bit on the strong side - 1.3% (instead of intended 1.25%).
If you consider that that 1 liter is really only 962.5g of water at 94°C (201.5°F), your real brew ratio (in mass) is 1.039 times higher (3.9%) than by volume. This applies to both the European and the North American brew charts (like the ones you can find online).
Whether or not your taste needs are met depends on whether you're sensitive to extraction or to strength.
If your taste is sensitive to strength, then you might trend lower to meet a tasting "strength" within a range of flavor that's still "in the ballpark" of extraction but not what you think it actually is. i.e. you'd be targeting 19.1% extraction. This also would match the brew chart for a given brew ratio and strength (assuming that your brew ratio is in mass).
If your taste is sensitive to extraction, and especially if you're outside the range of "in the ballpark", then you might be trending higher to achieve your taste goals given a particular brew ratio - and the variance in strength is not as much of an issue.
It all depends on the direction of the calculation and what you're sensitive to.
It does make me wonder what other assumptions we're making about the relevancy of the brew control charts.
------------------------------------------ ----------------------------------------- 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: 406 Location: California Expertise: I like coffee
Grinder: Kyocera CM-50 Vac Pot: S/S Moka Pot Drip: Aeropress
Posted Thu May 10, 2012, 12:48pm Subject: Re: Coffee Extraction Discussion, Questions for the membership:
Netphilosopher Said:
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.
When you weigh something on a scale you measure two things, the sample weight (mass * g) and its bouyancy in air (unless you have an evacuated chamber). If the densities of the sample and calibration weight are identical there is no correction. Steel has a density of about 7.9 g/cm^3 and coffee has a true density of....? I'm not sure, but I believe it's something a little greater than water.
For example, if you were to measure out 100.00g of olive oil (density of 0.9 g/ml) on your calibrated 0.01g scale the actual sample mass would be about 100.12g. Would this matter? It depends.
Netphilosopher Said:
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.
Could they all be off in the same direction? Maybe the statistics are on your side, but if you really wanted to you could buy a class F1 or F2 weight for about $20. It doesn't sound like that's necessary, especially if all you need is to measure coffee to something a little better than 0.1g.
Isn't TDS concentration typically defined as dissolved solids divided by solution volume? The equation above is TDS / solvent.
For normal concentration coffee that doesn't matter much but for higher brew strength it becomes more significant.
The most convenient way to measure coffee concentration is mass of dissolved solids divided by mass of solution. I'm pretty sure that's what a VST refractometer reports and I'll bet it's what you've been measuring with oven dehydration.
If you do this it changes the "standard" equation a little:
where the standard absorption factor is 2.3 instead of 2.086 or whatever. So many significant digits is pretty funny for something that is so variable!
Posted Thu May 10, 2012, 7:02pm Subject: Re: Coffee Extraction Discussion, Questions for the membership:
Netphilosopher Said:
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.
Not sure what you mean here. The brew charts don't predict, they simply input two of the three variables (brew ratio, %TDS, Extraction Yield) and calculate the third.
Posted Thu May 10, 2012, 7:07pm Subject: Re: Coffee Extraction Discussion, Questions for the membership:
Netphilosopher Said:
If you use 55g/1 liter of hot water, and achieve 1.24% strength, your calculated extraction is 20% on the classic brew chart. This is actually the same thing as using 55g/962.5g of hot water.
BUT if you use 55g / 1000g of hot water and achieve 1.24% strength, your calculated extraction is only 19.2% (because you achieved the same strength but used a higher brew ratio relative to volume to get there). On the chart, it's the same thing as using a brew ratio of 57g/1 liter and achieved 1.24% strength.
Yes, this error was identified and incorporated into VST's Extractmojo and MoJoToGo software. Many people nowadays would say that 19%, not 20%, is the center of their "sweet spot" for extraction yield.
Posted Fri May 11, 2012, 4:54am Subject: Re: Coffee Extraction Discussion, Questions for the membership:
andys Said:
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.
Not sure what you mean here. The brew charts don't predict, they simply input two of the three variables (brew ratio, %TDS, Extraction Yield) and calculate the third.
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.
Extraction = Strength * ((1/Brew Ratio) - Absorption) is the closed solution, where absorption is approximately 2.068.
Look at the chart, at approximately 5.5% brew ratio and 1.24% strength the answer is 20% extraction. at 1.36-1.37% strength, extraction is 22% at 1.12% strength (1.1170% ) strength, extraction is 18%
So, at 18% brew ratio, measure a strength of 4.47%, the extraction is 15.6% - yet this tastes pretty much exactly like a brew with 6% brew ratio with a strength of ~1.60% (where the extraction is 23.5%), when both are diluted to 1.2-1.3% strength. (these approximate by memory, don't have the data with me right now).
What is the correct answer? Taste, of course. By taste, these two when diluted to same strength are well within taste variation - the 18% brew ratio is in NO POSSIBLE WAY underextracted. This also isn't just the mass-density variation issue - we're talking something that tastes >22% extraction but calculates to significantly less than 17% extraction. These aren't VST or measurement errors - the brew chart is not relevant to the areas of interest and the method of brewing (immersion).
What I'm working on now is plotting the data, assigning and optimizing the balance of parameters, with a probable adjustment in the absorption parameter. Then, identifying the areas in between, picking some "checkpoints" and brewing those to validate the new model. Interesting stuff for a hobby... 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
No, the old researchers were also quite good at units - a concentration, by definition, is the percent of the solute in the solution by mass. That's the weird thing, they identify brew ratio as a ratio of mass to volume of solvent, but concentration is definitely %mass of the solution totalmass. I'm sure it was a convenience thing - dating back into the late 1800s, the recommendation of brew ratio is like a recipe - cups of coffee to cups or gallons or fluid oz of water. Just like cake recipes - standard measures of volume have been and are easy to come by, precision scales until recently were definitely NOT.
jpender Said:
... The most convenient way to measure coffee concentration is mass of dissolved solids divided by mass of solution.
where the standard absorption factor is 2.3 instead of 2.086 or whatever. So many significant digits is pretty funny for something that is so variable!
Couple checks (directly from the chart, European but overlay of N American and Euro are essentially same, just extended range for the Euro chart):
1.55% strength and 9% brew ratio is 14% extraction. 1.45% strength 5% brew ratio is 26% extraction. 1.65% strength 6.5% brew ratio is 22% extraction. 0.95% strength 5.0% brew ratio is 17% extraction. 1.30% strength 5.5% brew ratio is 21% extraction. 1.15% strength 7.5% brew ratio is 13% extraction
These all work out with the Extraction = Strength * ((1/Brew Ratio) - Absorption) equation when absorption is a constant at 2.0678.
Revising this to your form makes it impossible to find a constant for the absorption - and if you don't know that then it becomes an unknown (and an extra dimension).
------------------------------------------ ----------------------------------------- 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
There are a number of different ways to represent concentration and mass/volume is certainly one of them. Illy uses g/L to represent espresso strength, but I wasn't sure what the standard is for normal coffee.
The SCAA literature I could find only shows it as a percentage. The brewing control chart gives the brew ratio in g/L so it didn't seem crazy to assume that strength was in similar units.
Netphilosopher Said:
Revising this to your form makes it impossible to find a constant for the absorption
It's possible. I believe VST uses the same form of the equation (do you use mojo?). What isn't possible to is EXACTLY match what the mass/volume formula for strength produces.
If you choose 2.3 for the absorption constant (2.068 + 0.2 extraction) the difference between the two charts is insignificant over the pictured range. It's only when you're well outside what is shown on the chart that it starts to make any noticible difference.
But if you're going to use mass/mass concentration your formula has to reflect that or else it's nonsense... assuming you believe that absorption really is constant for a given mass of grounds.
I don't do pourovers, but my Aeropress and moka pucks are always well below 2.0 absorption.
jpender Senior Member Joined: 11 Jul 2011 Posts: 406 Location: California Expertise: I like coffee
Grinder: Kyocera CM-50 Vac Pot: S/S Moka Pot Drip: Aeropress
Posted Fri May 11, 2012, 10:33am Subject: Re: Coffee Extraction Discussion, Questions for the membership:
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.
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