Posted Fri Jun 1, 2012, 10:38am Subject: Re: Coffee Extraction Discussion, Questions for the membership:
First couple shots at varying brewing temperatures:
15:200 (~7.5% Brew Ratio) inverted AeroPress. Strike temperature recorded only (temp at initial pour). Dollop in, mix, remaining poured by 30seconds.
209°F 3min 1.45% (BW=199.84, Produced = 178.73) 170°F 3min 1.26% (BW=200.49, Produced = 180.99) 170°F 10min 1.46% (BW=201.97, Produced = 177.85) 209°F 10min 1.46% (BW=200.92, Produced = 177.33)
Still working out what the full mapping is going to look like, but it seems that to define the time vs. extraction, I have to obtain the resulting strength at a point or two up to about 3 min, then something where the brew has equalized. This is really going to increase the amount of brews I have to do. I'll probably have to map this out for 3 grind levels to understand what happens with equilibrium and the rate of solvation. That's planning about 18 cups of coffee initially (3 steep times X 2 Temperatures X 3 grind levels). Maybe a mid-temperature if required.
Another observation: during brewing, there's a few physical phases I noticed: -Bloom -settling/stabilizing, where the bloom has subsided a bit but there's larger pieces of the grounds still floating. -Large particles sink, I call this when the grounds "drop". This seems to happen fairly quickly.
On the high strike temp brews, this grounds drop at this grind level happens around 2-3 minutes. With the lower temperature, the grounds drop around 6 minutes. I'm wondering if this is a potential signal that the brew is approaching equilibrium.
------------------------------------------ ----------------------------------------- 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 Jun 1, 2012, 10:41am Subject: Re: Coffee Extraction Discussion, Questions for the membership:
I also did some attempts at high brew ratio using the BCM-4C drip brewer. Very Fine grind, 75.6g coffee (EoC 100% Colombia), Brew water was 420g+15g for evaporation went into the reservoir. I had to pulse the brewer to draw out the brew cycle, because of the fine grind it took a while to percolate through. Even so, I attempted to brew it as high an extraction as possible, but only managed to get a strength of 5.13% for a 299.9g yield. (~20.35% extraction).
Then, I decided to do something interesting, and keep adding brew water and checking the strength of each successive yield, until it wouldn't extract anymore.
299.9g at 5.13% ; 15.38 TDS, Incr Extraction=20.35%, Cum Extraction=20.35% +5.14g at 2.4% ; 0.12 TDS, Incr Extraction=0.16%, Cum Extraction=20.51% (Stuff that dripped out of brew basket) 500.4g at 0.53% ; 2.65 TDS, Incr Extraction=3.51%, Cum Extraction=24.02% 719.2g at 0.17% ; 1.22 TDS, Incr Extraction=1.62%, Cum Extraction=25.64% 720.9g at 0.08% ; 0.58 TDS, Incr Extraction=0.76%, Cum Extraction=26.4% 721.7g at 0.04% ; 0.29 TDS, Incr Extraction=0.38%, Cum Extraction=26.78%
(and the stuff that dribbled out of the brew basket was registering between 0.00 and 0.03%)
So, then I tried a one step brew attempt at maximum extraction at ~4% Brew Ratio in the BCM-4C: 15g coffee, fine grind, 375(+15)g brew water in the reservoir. Had to pulse the brewer to extend the brew time. Produced 346.3g at 1.13% strength, 3.91g TDS (basket drips were ~0.02-0.04%) for a one step extraction of 26.1%
So, not content to stop there, I decided to try an extremely fine 10g coffee at 4% brew ratio in the AeroPress. I chose a 12 minute contact time with agitation nearly constantly. 10g coffee : 247.23 g water for an effective brew ratio of 4.04%.
Resulting strength was 0.99%. Implies a yield-based extraction of 23.1%, or immersion calculation of more like 24.7%. I won't comment on taste, just looking at the extremes I have to go to get to maximum practical extraction, this shows up at the higher brew ratios.
So, if I run another ~300g through the remaining coffee (and here's the kicker), in steps (add 20-40g hot brew water, stir, press, repeat), I can extract some more. But not a lot more.
303.3g produced at ~0.10-0.12% strength, on average about 0.11%. That's another 0.34g of TDS, bringing to total possible extraction to ~2.65g from 10g of coffee.
(just for good measure, I did one more but the resulting strength for ~40g was essentially 0.00 or "sample out of range")
So, I'm fairly convinced that practical max extraction is a bit more than 26%, and normal brewing extraction is maybe around 25% for immersion, 26% for percolation at low brew ratios.
High brew ratios for percolation method (auto drip) are difficult to overextract (by high I mean >12%). The percolation rate is just too slow that you'll overrun the basket, and the flow through the bed just doesn't seem to be able to extract at fine grind.
I suppose I could try a coarse grind - see if the longer contact time makes up for the fast percolation rate...
So, now I've found a way to determine maximum extraction - go ahead and brew, and then brew some more until you can't. Keep track of everything you extract.
------------------------------------------ ----------------------------------------- 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
That makes 27 cups. Does brew ratio affect extraction rate? Agitation? What about degree of roast? If you include those as variables you'll need to brew 3^6 cups. And if you insist on at least one replication per case that makes... more than year's worth of coffee!
Netphilosopher Said:
On the high strike temp brews, this grounds drop at this grind level happens around 2-3 minutes. With the lower temperature, the grounds drop around 6 minutes. I'm wondering if this is a potential signal that the brew is approaching equilibrium.
Or how long it takes them to fully infuse with water. If infusion rate is what is limiting extraction on large particles then it might be the same thing.
Netphilosopher Said:
So, now I've found a way to determine maximum extraction - go ahead and brew, and then brew some more until you can't. Keep track of everything you extract.
At this point would it be easier and possibly more accurate to oven dehydrate the grounds?
By the way, how well can you correlate extraction yield from oven dehydration with what your refractometer tells you? To what extent can you simply take what you've filtered out of the beverage and add that to the dried grounds to get the same number? And what kind of filtering do you need to do to achieve this?
I'm curious because when I measure extraction yield of a moka pot brew through dehydration the value is always high even when the coffee tastes sour. I know there are a fair amount of solids in moka coffee; is it enough to simply filter the coffee through an Aeropress or does too much pass through this way?
Posted Sat Jun 2, 2012, 3:11pm Subject: Re: Coffee Extraction Discussion, Questions for the membership:
jpender Said:
That makes 27 cups. Does brew ratio affect extraction rate? Agitation? What about degree of roast? If you include those as variables you'll need to brew 3^6 cups. And if you insist on at least one replication per case that makes... more than year's worth of coffee!
Or how long it takes them to fully infuse with water. If infusion rate is what is limiting extraction on large particles then it might be the same thing.
LOL - I'm not going to test every condition, just work within the design space and try and define the brewing space.
I think there's a particle size limitation that I'm encountering - like the explanations of leaching of organic materials, there's a depth of penetration limit that doesn't seem to be practical to diffuse any of the solute out from the core of the particle. I've always wondered why no matter how long I let press pot grind sit in the pot, it just doesn't seem to taste overextracted, or how people I've discussed cupping with have never gotten to cool cups of coffee and found the coffee completely undrinkable after a half hour. Even checking cupped coffee with a half hour for strength, I'm seeing data that supports the immersion brewing extraction hypothesis. The grind is pretty coarse for cupping - and this seems to prevent over 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
Posted Sat Jun 2, 2012, 3:37pm Subject: Re: Coffee Extraction Discussion, Questions for the membership:
jpender Said:
... At this point would it be easier and possibly more accurate to oven dehydrate the grounds?
By the way, how well can you correlate extraction yield from oven dehydration with what your refractometer tells you? To what extent can you simply take what you've filtered out of the beverage and add that to the dried grounds to get the same number? And what kind of filtering do you need to do to achieve this?
I'm curious because when I measure extraction yield of a moka pot brew through dehydration the value is always high even when the coffee tastes sour. I know there are a fair amount of solids in moka coffee; is it enough to simply filter the coffee through an Aeropress or does too much pass through this way?
I know you've asked several times about home dehydration - I am only about a third the way through investigating the correlation. Some quick points I've got enough data to draw some inferences:
-if you have minimal fines on a coarse grind and a decent cone burr grinder (by decent, I mean you're not using the P.O.S. cuisinart grinder), home dehydration will work ok. Particle size will be large, and fines produced will be fairly low.
-If you're any coarser than a step less than press pot (maybe <700microns average), then the AeroPress filter won't work well for filtering. The finer the grind, the more smaller particles are generated. The greater the dehydration error.
-Surprisingly, cone filtration through a Melitta filter works pretty well. Less so if you filter the coffee only, better if you dump the slurry into the cone. I think this is helped by "cake filtration" of the grounds, but there's the initial amount of the coffee that went through the filter without percolating through the grounds bed - and it will carry fines with it.
-the worst error is using something approaching espresso grind and an unsupported AeroPress filter. Like Vince F. has mentioned to me, the mild pressure blows the fiber of the paper filter open and you get a decent amount of fines through.
-Doubling the filter doesn't seem to help. Supporting the filter with a Coava does seem to drop the pass-through of the filter, but the greater the amount of fines the more will still get through.
So, I'm sure the next question is "how much is the error?" The answer is, it depends.
I've done a handful of dehydrations over the last months since I got my VSTcr. Some of my largest differences between evaporation/dehydration and the VSTcr were always with fine grind (where I was desperately trying to make over-extracted coffee). I was carrying an undissolved solids error into the dehydrated solids.
The VST filters are not cheap, but they are pretty darn effective at filtering. I estimate these are approaching 1-2 micron particle filtration - very impressive. My latest attempts were producing coffee, measuring the strength of said coffee, then dehydrating the sample to measure the resulting residual solids.
Even with VST filters and fine grind, I still get about 4-5% difference between the dehydrated solids left behind vs. the VST backcalculated TDS. I try to produce ~200g of coffee in the 2% strength range for dehydration (makes the measurement have a bit more discretion). Initially, it looks like the difference drops to about 2-3% (***but pretty close to the limit of my measurement discretion***) using coarse grind.
With the AeroPress filter and fine grind, I get a whopping 15% to 18% difference in residual solids and backcalculated TDS.
I've also produced samples that are VST filtered, then centrifuged for 10 minutes and sample drawn from the supernatant, THEN checked for strength and dehydrated. The error drops to about 2% or less (difference of .08g in ~4g of solids). In all cases, the dehydrated result would imply a higher strength.
The last thing I've been playing around with - produce a sample of coffee, check the strength, then dehydrate the sample to obtain the residual solids. There will be a difference, and you'll produce more solids than the VST would say you should.
Then, re-constitute the solids with hot distilled water. Measure the strength (since I now have control over the amount of water I add, I can make the strength anything I want, I try to make the strength target around 5% - if I have 4.10g of solids, I'll attempt to make about 82g of total solution). In a fine grind case with a doubled AeroPress filter unsupported, I produced about 4.42g of solids (where the VST was saying I should have produced about 3.85g of solids, ~1.76% strength 225g). I then took the solution, centrifuged it for 10 minutes, drew off the supernatant (and of course saved it) and saw a significant amount of solids at the bottom of the tubes.
Then, I rinsed all of these solids with about 30ml of distilled water into a couple of test tubes, then centrifuged THOSE some more to concentrate the solids. I drew off the clearish supernatant, then used about 10ml of distilled water to rinse the remaining solids out of the two tubes (now a yucky looking grey-brown thick consistency something), and into a dehydration bowl. Those weighed 0.49g! That alone was over 10% of the error.
The second time I did this I recovered 0.28g undissolved solids out of 4.10g of recovered TDS, where the VST was implying 3.66g of TDS with the reconstituted "coffee".
I've also checked centrifuging vs. the VST filter - I took centrifuged coffee supernatant, ran half through the VST filter and the other half just as is, and dehydrated both of them - and got the same amount of TDS. If I compare a VST filtered sample (NOT centrifuged) to a supernatant of same coffee, after dehydration, I get about 1-2% more solids in the VST filter. I can conclude from this that 10minutes centrifuge at maximum is the most effective home method I have for separation of undissolved solids.
So, bottom line is dehydration will carry some error with it unless you filter it with a VST filter or centrifuge the sample. The grounds drying will be somewhat close, but will also carry the error as well, with no way to recover it. Unfortunately, this error will be dependent on the filter, the grind size and how much fines are produced with the grind.
------------------------------------------ ----------------------------------------- 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 Jun 4, 2012, 9:46am Subject: Re: Coffee Extraction Discussion, Questions for the membership:
The latest folly I think may answer the question of "what's left in the puck?"
I thought that if I brewed some coffee with immersion method (inverted AeroPress), then run a 2nd stage "rinse" of the wet grounds with known amount of water, I may be able to tease out roughly how much of the dissolved TDS is in solution vs. how much is just not removable due to the absorption of the grounds.
I first tried this quickly on the grounds left behind from a 20.3% extraction (yield-based) from the BCM-4C brewer. I let the grounds drip until no more (very low strength).
Then, I loaded these wet grounds into the AP, and sqeezed some more. Not surprisingly this was also very low strength and the same as the strength of drippings measured (approximately 0.50%, initial brew was ~1.5% strength).
Then, I added a bit of some COLD water in, quickly stirred and pressed - much of what I put in came back out, with extremely weak strength (registering between 0.18-0.22%).
Essentially, there is little useable coffee left behind in the auto drip brewer at the end of cycle. All of the stuff produced tasted very weak and very nasty.
Then, I decided to try this on immersion. I figured if I brewed coffee, kept track of what was trapped in the filter and the wet spent grounds, put a known amount of COLD (i.e. NON-extracting, just diluting whatever is there and allowing it to be expressed) water, whatever useable coffee is in the puck would mix with the new brew water and produce... something. Very low strength if the stuff left behind was not "extracted" or "expressable" or a significant amount of the water was not available to make coffee in the slurry. I'd expect measurable strength if there is still "useable" dissolved solids.
Results and discussion next:
------------------------------------------ ----------------------------------------- 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 Jun 4, 2012, 9:53am Subject: Re: Coffee Extraction Discussion, Questions for the membership:
All fun experiements start with prediction. Once you have a model, prediction is part of the process of attempting to disprove or challenge a hypothesis.
Prediction:
Coffee = 25g, Brew Water = 200g.
I know from experience that my filter cap retains about 0.7g of coffee, physical absorption is around 1.3 (1.33 including the cap retention).
Using this brew ratio and this grind (commercial drip grind) at ~5.5minutes brew cycle produces consistent 21.5% extracted coffee in the BCM-4C (at a strength around 3.4% and absorption around 1.7)
Using this brew ratio, grind and 8 minute contact time with the AP creates coffee around 2.5-2.7% strength, I was hoping for around 2.6 or so.
Using those assumptions, I predicted:
Spent Grounds 57.5 Produced coffee: 166.8 2.617% strength at 21.5%(Immersion calculation) extraction, or 17.46% using yield-based extraction.
This implies that the spent grounds consist of three things
-Undissolved/Unextracted Coffee Solids (UCS) - this would be = (Coffee - (Extraction X Coffee)) -recoverable already dissolved solids (in solution) with recoverable water as "coffee" -water unavailable as a solvent (absorbed in the unextracted coffee)
So far, there's two estimates of "extraction", immersion (21.5%) or yield (17.46%).
Immersion Theory predicts: -UCS = 19.625 -Coffee at 2.617% strength = 38.575g -No water is considered "unavailable" as a solvent.
Yield-based extraction predicts: -UCS = 20.635g, and since the beverage has all of the "extractable" stuff (the basis of my hypothesis for why yield-extraction is not correct), there should be little left over to make provide TDS for whatever liquid is left. -The rest of the spent grounds (36.865g) would consist of (if Yield-based extraction is correct) primarily water that was not extractable/expressable, absorbed and unavailable for extraction, or a contain a negligibly small amount of undesired TDS. -TDS in solution would be very small (or the UCS would have to change, which means that we cannot use the yield-based extraction as a basis for assessing extraction). The only TDS as part of the experiment would be anything in the cap/filter.
So, if I add back about 38g of water, whatever already dissolved solids would be diluted by a known amount, and we have enough to back calculate.
If most of the liquid in the grounds is coffee, then I would predict the added water would dilute 38.757g of coffee at 2.617% strength, and create coffee at 1.31% strength - which would be expressed and measurable.
If there is nothing left to extract, then the resulting rinsed solution would be very weak (because it had not been extracted and I'm not extracting anything more because I'm only adding 40°F water for less than 30 seconds). Technically, it should be just about zero.
------------------------------------------ ----------------------------------------- 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 Jun 4, 2012, 10:05am Subject: Re: Coffee Extraction Discussion, Questions for the membership:
Results:
25.00g = Coffee 199.73g = Brew Water 0.57g = Cap retained 54.83g = Spent Grounds 168.64g = Coffee Produced 2.61% = Strength
21.41% = Immersion Calculated Extraction 17.63% = Yield based Extraction.
IMMERSION THEORY: 19.64g = Undissolved/Unextracted Coffee in spent grounds (Immersion Calculation) 35.75g = Coffee unexpressed at 2.61% strength (with 0.93g TDS in solution + 34.82g water, includes the 0.57g retained in the cap)
0.93g = TDS theoretically available and already extracted/dissolved to make coffee.
YIELD THEORY 20.59g = Undissolved/Unextracted Coffee in spent grounds (Yield Calculation). 34.24g = Basically water (since whatever was extracted is "unextracted") 0.57g = Coffee @ 2.61% strength trapped in cap
0.015g = TDs available/already extracted (trapped in filter/cap)
I added 35.31g of cold water to the grounds, quickly stirred and replaced the same filter/cap and pressed. There was a bit of evaporation while I got everything set up (the cap lost 0.12g and the AeroPress with spent grounds lost 0.33g of water to evaporation).
0.45g = Cap Retained Coffee (originally 0.57g) 54.50g = Spent Grounds prior to Additional Water (originally 54.83g) 35.31g = Added Water
1.06g = Cap Retained After dilution water press 63.27g = Spent grounds after dilution water press
25.76g = produced diluted solution 1.19% = diluted solution strength.
Because of the evaporation, I can treat the added water as more like 35.31 - 0.12 - 0.33 = 34.86g
So, I have an unknown amount of solution in the previous brew at 2.61% strength, but when I add 34.86g of water it becomes 1.19% strength. Since the second step is dilution only, and it is diluting the already dissolved TDS in the spent grounds and the cap, we have
Water as coffee with unknown TDS making a solution with strength of 2.61% Water + 34.86g with unknown SAME TDS making a solution with strength 1.19%
Using iteration or solver, a plausible solution of TDS = 0.763g Water as coffee = 29.21g Makes a solution in the spent grounds and cap of 2.61% strength,
when you add 34.86g, you get 0.763/64.07g = 1.19% strength.
So, now the picture emerges of the spent grounds after the first press consisting of:
55.4g = Total Spent Grounds + Cap retained coffee 0.57g = coffee @ 2.61% Strength trapped in cap 0.763g = TDS to make coffee @ 2.61% strength 28.447g = Water as coffee @ 2.61% strength 19.87g = Unextracted Coffee 5.75g = Water unavailable for solution
20.52% = Revised Extraction based on remaining unextracted coffee solids (25g -19.87g)/25g
There's other sources of error - my VSTcr may be reading low. Or high. It's not calabratable, and all my checks show that it is "within expected accuracy" after discussing with Vince. My scale may have error (though this is vanishingly less likely since I've checked all of my cal weights on certified scales - they're surprisingly close). Maybe adding cold water still "extracts" more stuff and the diluted strength is more strong than it actually is and is overstating the amount of "coffee".
There's also the question of transported UNdissolved solids that are in suspension in the produced coffee. In the past, this can be another 0.3g - and are considered "spent" (i.e., if I could, I would have wanted to keep them in the spent grounds).
But assuming I'm close enough, I've gotten enough information together to ask:
So, which is most correct? Immersion method where A = -(E), 21.5%? Yield based (where A is method dependent, in this case = 1.33) at 17.5%? Traditional Brew Chart (mass converted) A = 1.76 where extraction would be a dismal 16.33%?
Interestingly, my original thought was to make A=0 when I started this extraction exploration, which makes all of the immersion calculations very simple. A=0 would calculate extraction at 20.9%.
Back calculating the A based on the 20.52% extraction would predict A=0.15, probably sufficiently close to zero as to call it such.
Regardless, the answer is not in the range of anything close to a traditional extraction or brew chart - the bottom line is that there is definitely useable (significantly useable) coffee left in the grounds with immersion methods. This conclusion should not be so surprising. Percolation and wash methods are constantly transporting solutes and continually filtering. Immersion methods do not.
The concentration of the produced coffee over time is also different. Percolation/Wash starts high concentration and drops as the extraction goes on. The concentration of the immersion method coffee starts low and increases to an equilibrium. They can and probably do respond differently to temperature.
So, another piece of the puzzle.
------------------------------------------ ----------------------------------------- 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: 401 Location: California Expertise: I like coffee
Grinder: Kyocera CM-50 Vac Pot: S/S Moka Pot Drip: Aeropress
Posted Mon Jun 4, 2012, 2:14pm Subject: Re: Coffee Extraction Discussion, Questions for the membership:
Netphilosopher Said:
So, bottom line is dehydration will carry some error with it unless you filter it with a VST filter or centrifuge the sample. The grounds drying will be somewhat close, but will also carry the error as well, with no way to recover it. Unfortunately, this error will be dependent on the filter, the grind size and how much fines are produced with the grind.
That's what I thought. I'm disappointed in that it seems that I cannot expect to reliably adjust for it.
For moka coffee it might make sense to use solids yield like with espresso, instead of extraction. But to calculate the beverage strength you need to know how much of those extracted solids are dissolved versus undissolved.
Which leads to the question, how does mojo/VST do it?
With a refractometer all you know is the TDS from the filtered sample. The only way to determine the amount of undissolved solids, aside from dehydration, is through some function that relates dose and TDS to total solids. If you can do this with espresso why couldn't you do it with moka?
Posted Mon Jun 4, 2012, 2:50pm Subject: Re: Coffee Extraction Discussion, Questions for the membership:
jpender Said:
That's what I thought. I'm disappointed in that it seems that I cannot expect to reliably adjust for it.
For moka coffee it might make sense to use solids yield like with espresso, instead of extraction. But to calculate the beverage strength you need to know how much of those extracted solids are dissolved versus undissolved.
Which leads to the question, how does mojo/VST do it?
With a refractometer all you know is the TDS from the filtered sample. The only way to determine the amount of undissolved solids, aside from dehydration, is through some function that relates dose and TDS to total solids. If you can do this with espresso why couldn't you do it with moka?
Nope you're not misunderstanding it at all. VST/mojo is NOT an EXTRACTION measurement device. It measures %TDS - in fact, that's ALL it measures (internally, it measures refractive index of a filtered liquid, and then converts and reports this in %TDS - but it does not display the actual nD).
As far as I know, there really is no way to measure "extraction" per se directly - everything is by measured inference. Either you're keeping track of solids transferred to the beverage, or you're backcalculating from strength.
Moka - just use the solids yield. That's as accurate as it gets, since it's a wash method (forced percolation). How much coffee did you use? How much coffee beverage did you produce? What's the strength of the beverage?
E = S Cp/C where E=Extraction S=Strength Cp=Coffee Produced C=Initial Dry Ground Coffee
If you calculate >22%, it's highly likely the extraction carried too long or too strong and now you have some of the end unwanted stuff in your coffee.
Regarding methods of determining strength:
The old method uses a filtered sample of the coffee (or settled using overnight settling or centrifugation), and dehydration of the clarified sample of the beverage. (the filtering removes as much of the undissolved solids as possible to reduce this error)
The VST uses refractive index to infer the strength (aka concentration) of the sample. The VSTcr is less sensitive to undissolved solids (since suspended colloids of a large enough size do not affect the refractive index of a fluid, just the clarity), but is subject to particle reflective error (an error that exists with laser refractometers, where small particles can scatter the beam used to measure the index of refraction). You just need to filter out most of the big chunks - so a gravity drip PAPER filter with a bed of grounds is good enough.
Basically, what I've found is that if you can put it in a tube and read through to see the writing clearly on the other side, it's "good enough". If it looks cloudy (like an aeropress, french press, or most of the metal filters), you should filter or make sure you try and settle it for a few minutes at minimum, or you start to get a fair amount of data scatter. The median reading of several measurements seems to work fine and is quite repeatable, but it can be disconcerting to see measurements fluctuate +/- 0.04% because you're trying to read a cloudy sample.
------------------------------------------ ----------------------------------------- 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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