germantownrob Senior Member Joined: 2 Dec 2007 Posts: 2,018 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 Wed Feb 22, 2012, 11:04pm Subject: Re: coffee refractometer
Dave, it is pretty common around here when someone new does not give personal info it makes people suspicious. This is a topic that has some heated conversation that runs deep.
Anyway I am really trying to learn more about espresso extraction, this topic kicking back in gear excited me, I do hope it moves forward with meaningful info instead of........
If you're serious about making these measurements, look up the engineering definitions of "accuracy," "precision," and "resolution." They have very specific meanings that may be different from colloquial language. If you're going to ask technical questions using these words, please be careful to say what you mean and mean what you say.
Kafeman Said:
what the VST coffee refractometer instrument accuracy is on the raw refractive index
For the second time I'll tell you I don't know the accuracy in refractive index of the VST refractometers; VST does not offer that specification. The offered specs for the newest LAB model are in the link I previously supplied to you and refer to coffee TDS: "accuracy +/- 0.05% (0.00-4.99%) warranted, and precision +/- 0.02% (typical)"
If you want to know the instrument's accuracy in RI, you already have been given the info you need to guesstimate an answer. In doing so, you must bear in mind that that "typical accuracy" is significantly better than the "warranted accuracy." If that were not the case, Vince would lose time and money trying to satisfy warranty claims. To avoid such claims, I know that he personally runs a QC test procedure on every unit before it ships.
Kafeman Said:
Ouch! Real name? You know I'm Dave - IMO, if you see something you don't agree with, there is no reason to take that tone with me
I'd suggest you grow a thicker skin and take responsibility for teaching us something we don't yet know.
RE: thick skins, if you read the posts that came before you entered this thread, you'll see that the previous poster pretty much accused me of doing paid work for VST and being less than truthful about it. I don't appreciate this, but he has as much right to post here as I do.
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 Feb 23, 2012, 8:22pm Subject: Re: coffee refractometer
Netphilosopher Said:
Yes, but I didn't have my notes with me. If I recall, dehydrating at 300°F ended up an extra 0.1g out of the grounds and not a measurable difference in the dehydrated liquid. Something like a tenth of a gram went missing and it didn't seem right to let it sit on the counter for an hour and let it absorb that tenth of a gram just to make the numbers come out right. Something like 22g original, normally weigh (after extraction and dehydration) 17.4-17.8g, the dried solids left behind on evaporation weigh the balance - except for high temperature drying of grounds, which lose a tenth of a gram between the two.
Doesn't sound like much, but in those quantities, every tenth of a gram lost in the grounds weight is around a half percentage of extraction.
Thanks for the response. I've tried dehydration numerous times and have always felt unhappy with the way the finishing weight seemed to be a moving target. Since, as you point out, an error of 0.1 gram translates into a difference of 0.5% extraction (for 20g of coffee) the fact that I saw the weight continuing to change by more than that bothered me.
I suspect my issue was impatience. Rather than wait hours to use an oven I tried using the microwave. Careful as I tried to be, it just got too hot at the end. Some of my samples actually smoked!
So I tried it in the oven again. I made two nearly identical 19+ gram batches in an Aeropress, mixed the wet grounds together and then divided them as equally as I could (difference of 0.03g). Then I dried one half at 215°F (which took forever) and the other at 300°F which took about half as long. There was still uncertainty as to when it was done. The weights seemed to rise for the first several minutes of cooling and then stabilize, something I had never seen with the samples I had microwaved. After more than an hour each of the oven dried samples (covered in a layer of foil) had a stable weight, to the precision of my scale (0.01g).
What I didn't see however was a difference between the 215°F and 300°F dried samples (other than time to dry). They weighed almost exactly the same, just a few hundreths of a gram difference. The size of 0.1g of dried coffee is quite small, enough so that it would be very easy to be off by that amount if one isn't very careful. Even the coffee that I couldn't quite scrape off of the AP plunger or that stuck to the utensil I scrape it with might be significant.
The fact that you are able to get consistent results that add up is impressive, both in your skill and your patience. I'm glad I don't have to oven dry my used grounds for hours in order to have good coffee. If I did I might switch to Folgers, or tea.
Kafeman Senior Member Joined: 18 Feb 2012 Posts: 24 Location: FL Expertise: Just starting
Posted Thu Feb 23, 2012, 10:13pm Subject: Re: coffee refractometer
Andys
Whatever, Andy, I prefer to enjoy my coffee rather than argue with someone who insults me at every point he can figure out how like a politician who seems to pump himself up by stepping on me and plenty of others as I look over your history - and then tells me if I don’t like it to grow a thicker skin. Just because you've been around a while gives you no right to do this.
Your discussion on precision, accuracy and resolution is only the latest example of your attitude to berate and discredit anyone who you decide to be nasty to. I discussed accuracy and *you* responded with resolution which was irrelevant right then, but no, I don't slam you for bringing up a different concept, I just say I'm confused as to why you would say that; so I followed your lead, and if you were kinder you just would have been nicer and mentioned what you knew earlier if you thought it relevant, but no, and then you slam me for being confused with your mashing of this all together as if I originated the mess.
If I held you to the standard you hold me, I could trash you on each statement you make as well, putting a spin on it of course like you've done to me.
Remember again, I said, you were a star contributor (it was after seeing how you treated others and for a genuine fear of you as a senior member and something like this happening) and you even slammed me even for that, 'we don't have a star system here, keep on topic' - I don't know where your head is coming from half of the time since you invented all by yourself that I wanted to implement a star rating system here – I still can’t believe how you made that up).
I feel you only say what you want when you can get another nasty word in this thread with me. If I wanted to get into this sort of banter, I will lose with you, because I see all you will do is dissect every single thing I say and modify it to suit your mood and then send your missiles. If I respond you do it again and if I don't you get the last word. I can't continue that, even after 10 cups of coffee.
Just for clarity in case someone else would judge me by these damning posts, I haven't accused Andys of working for VST, he's talking about someone else and I don't have any idea who that person is except for what is written in this thread.
You have made federal cases out of my sharing my efforts at improving my own evaluation of my coffees, as if you were my boss breathing down my neck before I finished a project, asks where I'm at and then blasts me because I'm not done. You tell me I am "giving instructing" to people on refractometers, man, you are so far off it would have been silly to respond to that on this planet, any chemist will think this way; how you dreamed up I am instructing others again completely escapes me, and this crap about last names - look: I'm ok by forum guidelines and that is all that counts, so you got under my thin skin with that comment of personal crap.
As a newbie, I have taken far more on the chin than I should have, my fault, just because I thought it would be nice to gain your acceptance but I failed, and as a result I will just cease with my participation in this thread as it has become unpleasant for me and I have no wish to take on such an endeavor, is now only detracting thanks to your nasty grilling and as for your disrespectful clincher
take responsibility for teaching us something we don't yet know
That last bit of nastiness sums you up. I assume it was the royal "we", and I don't care, yeah, according to you I’m an irresponsible slacking off teacher so far, whatever... Exit stage right (soapbox vacant for all time)
Posted Fri Feb 24, 2012, 7:55pm Subject: Re: coffee refractometer
GlennV Said:
Personally I'm very happy with de facto standards. For example, AndyS says he likes likes his espressi at 19-20%, personally I prefer 18% when at 65% brew ratio. We might have different tastes or be drinking different coffees. More likely it's because he's got better kit - and I have to jump through too many hoops to get yield up to 19% with that small amount of water.
Believe me, I too sometimes have to jump through hoops to get yields up around 19%. Some batches of particular coffees seem reluctant to give up their solids (lighter roasts especially). Grinding finer and underdosing the basket a lot helps (eg, 18g dose in a 22g basket).
I'm told that grinding too fine for a particular basket will produce a silty espresso (as extra-fine fines pass through the perforations). But at the underdose levels I use, I have rarely noticed this.
BTW, there is a term in psychology for one's mental state when others are able to consistently extract higher yields from a particular coffee than you can: "extraction envy."
Speaking of which, I brought my grinder to Vince's house last summer and we pulled side-by-side shots comparing my Robur to his K-10. Using identical doses, similar brew ratios, and with grinders tweaked to give matching shot times, the K-10 yields were consistently about 0.5% higher. A small difference, but enough so that I was helpless to suppress mild extraction envy symptoms.
Presumably the K-10 burrs produce slightly fewer fines, which means you grind a little finer to get the desired shot time. That finer grind gives a bigger yield.
Some people may not have seen Dave Walsh's fascinating piece where he sieved out the fines and the extra-coarse pieces from some grounds. He was then able to make pleasing, non-bitter coffee from the mid-size particles at a 24% extraction level. Since the generally accepted extraction range hasn't changed much in the last fifty years, his experiment suggests that there's been little progress in grind quality during that period of time.
GlennV Said:
It's nice to know that it's not because we have a different notion of what 19% is though.
Posted Fri Feb 24, 2012, 9:39pm Subject: Re: coffee refractometer
Netphilosopher Said:
22 grams of coffee used. 385g of brew water in an Aeropress.
Press 1 yields 330g of coffee (because I don't press all the way through the puck, just until I hear air, and I have a wet puck left behind). I dehydrate the coffee, and the grounds, and get 4.2 TDS and 17.8g of dried grounds. The coffee is at target strength: around 1.27%, but the calculated extraction is only 19% (4.2/22).
Press 2 yields 360g of coffee (because I press every drop I can out of the puck, and yes you can get up to another 30g of coffee). I dehydrate the coffee and grounds, and get 4.5 TDS, and 17.5g of dried grounds. The strength of the coffee is the same for all practical purposes: 1.25%. Calculated extraction is 20.4%. Which one is right?
I like your methodology, but why not consider both results right? In the second case, you got an additional 30g of beverage, at 1.0% strength, containing 0.3g of solids. Not only was the strength of the last 30 g less than the first part, but the composition of the dissolved solids was likely different (more weak caramels, creosote-bitters, etc). Next time you could taste the two fractions separately and compare.
Netphilosopher Said:
For me it would be nice to take press 1, squeeze out the last 30g of stuff, and check the strength - if that's the same strength (and why wouldn't it be? The extraction is for all practical purposes completed)
You actually proved that it wasn't the same strength, right? Meanwhile, the extraction is not "completed" until you approach the physical limit of solubility (somewhere around 30% yield), which takes a much bigger volume of water run through the grounds.
Netphilosopher Said:
Why do larger grind sizes seem to retain more than finer grind sizes? Is this why espresso seems to have less absorption?
Posted Fri Feb 24, 2012, 10:25pm Subject: Re: coffee refractometer
andys Said:
I like your methodology, but why not consider both results right? In the second case, you got an additional 30g of beverage, at 1.0% strength, containing 0.3g of solids. Not only was the strength of the last 30 g less than the first part, but the composition of the dissolved solids was likely different (more weak caramels, creosote-bitters, etc). Next time you could taste the two fractions separately and compare.
You actually proved that it wasn't the same strength, right? Meanwhile, the extraction is not "completed" until you approach the physical limit of solubility (somewhere around 30% yield), which takes a much bigger volume of water run through the grounds.
I think I'm inside the discretion of my current measurement system. I have repeated this a few times, and I've also tasted the last squeezings - it tastes like the stuff in the cup, it doesn't seem to be weaker or stronger, and doesn't have any overbearing smokiness, creosote, and will also have the same basic fruits/florals as the stuff already in the cup.
andys Said:
BTW, how do you make 22g/385g batches in an Aeropress? That's huge.
Not exactly an Aeropress as most here would use it - although I have the material and an extra Aeropress I was going to convert into an AeroPress XL (eXtended length) with some co-polyester tubing).
In these cases, I use the press as a grounds separator in a full contact batch. Brew in a pyrex measuring cup, then into the press for grounds separation. The first 100-150g goes in (mostly coffee with little grounds) press and withdraw and swirl dump and press the rest. I only do it when I'm brewing that much at final strength, and usually only when doing experiments (easier for me to tell when <1% strength and when it's >1.5% strength, as opposed to trying to tell the difference between 2.2 and 2.5%). When I brew that much, I have to use my 450ml coffee cup.
You also have to make sure your cap is not bulged or convex (from multiple cycles) or the cap won't properly clamp the filter at the edges enough to keep it from pulling out during withdrawal. Also helps if there isn't too much liquid on the filter when you withdraw. Additionally, you can withdraw it far enough and then kind of wiggle the plunger sideways to break the seal and pull the plunger out without much vacuum on the filter. I've made every one of these mistakes and learned the workarounds the hard way...
------------------------------------------ ----------------------------------------- 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 Feb 24, 2012, 10:31pm Subject: Re: coffee refractometer
and yes, it takes a buttload of time to dehydrate 360g of coffee in a 215°F oven. LOL That's a set it and forget it for many hours endeavor.
------------------------------------------ ----------------------------------------- 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 Feb 25, 2012, 9:38pm Subject: Re: coffee refractometer
Netphilosopher Said:
I think I'm inside the discretion of my current measurement system. I have repeated this a few times, and I've also tasted the last squeezings - it tastes like the stuff in the cup, it doesn't seem to be weaker or stronger, and doesn't have any overbearing smokiness, creosote, and will also have the same basic fruits/florals as the stuff already in the cup.
I think I understand your rationale in doing these experiments. While the traditional method for measuring extraction yield focuses on what's in the cup (ignoring whatever liquid remains trapped in the grounds), I believe you are exploring whether the trapped liquid should also be considered as part of the extraction.
Following the latter procedure is a practical challenge, though, because we can only guess the composition of that extra liquid. We can't measure it accurately because by definition, we haven't pulled it out yet. And the physical process of pulling it out will change its composition, as agitation and turbulence come into play.
We know that the trapped liquid's composition will vary tremendously depending on the brew method. For cupping brews (where the grounds are gently spooned out of the cup), the trapped liquid will be almost identical to the liquid beverage. For full immersion style brews like french press or aeropress, the trapped liquid will be similar (but not identical) to the extracted beverage. In percolation style brews like pourover or espresso, it will be much, much weaker.* Exactly HOW much weaker depends on the brew ratio. Every brew method has a slightly different effect on this, and accounting for it will drive you crazy.
So I think it makes the art and science of coffee extraction far more complicated -- and due to all the ambiguities, ultimately less useful -- if we try and include the trapped liquid in our measurement process.
The gold standard of extraction measurement has always been comparing the mass of solids found in the evaporated beverage to the original mass of dry coffee. Although not a perfect method for every brew style, it is simple, repeatable, and gives a reasonable correlation to taste. The interesting thing is that when we use this classic, imperfect extraction measurement protocol, people's taste preference usually centers around 19% -- no matter what brew method is used.
*For example, the last bit of espresso that flows into your cup might be only 15% as strong as the first bit. The last bit of pourover coffee is also much weaker than the first.
Posted Sun Feb 26, 2012, 8:30am Subject: Re: coffee refractometer
andys Said:
I think I understand your rationale in doing these experiments. While the traditional method for measuring extraction yield focuses on what's in the cup (ignoring whatever liquid remains trapped in the grounds), I believe you are exploring whether the trapped liquid should also be considered as part of the extraction.
Following the latter procedure is a practical challenge, though, because we can only guess the composition of that extra liquid. We can't measure it accurately because by definition, we haven't pulled it out yet. And the physical process of pulling it out will change its composition, as agitation and turbulence come into play.
Not only the fact that we can't measure it because we haven't pulled it out yet, at a certain point we CANNOT pull it out. Some of it is absorbed in the cellulose of the grounds and only evaporation will pull the water out. It's why you can't "wring" a washcloth or paper towel 100% dry.
One thing I tried - ever do a fiber-siphon? Take a wet paper towel, put one end in a glass of water and the other end at a lower point - the wet paper towel acts like a siphon with the capillary action. Do this with sand and saltwater, and you get saltwater in the other side of the fiber siphon (but of course no sand). Squeeze out the paper towel and you get salt water, but the sand stays behind, and you get a salty paper towel if you dry it.
Then, brew some coffee. Set up the siphon and you get coffee on the other side, and it's pretty much the same strength as the stuff on the starting side. The paper towel is stained, and when you squeeze it out you get coffee, same strength. The paper towel will dry and smell like coffee.
In both cases, I get to a point where it is impossible to pull any more liquid out of the paper towel, yet it is still wet and still contains the liquid that was siphoned.
By inference, I can only think that any of the solution left behind in the grounds is probably the same concentration as the stuff being pulled out just before the extraction is ended.
(Oooohhh... I just thought of this, maybe i'll try it in a few weeks - siphon a solution from one to the other, then siphon distilled water. Does this "wash" the siphon out?)
Several things led me to investigating it, and the physical process of pulling the last drippings out CAN change its composition. It depends on how it's extracted, how far along the extraction is, the brewing method (immersion/infusion vs. washing).
Using the end strength to calculate the extracted solids and then back calculate the extraction percentage is partly dependent on whether there's coffee left, and how much is absorbed in the grounds. Less of an issue with espresso, of course (your area of expertise). The end absorbed espresso in the puck is so consistent that your particular extraction method probably lends itself VERY well to end strength back calculation. Same for fairly consistent wash brew methods like drip and pourover IF you are achieving the correct grind.
In the multithousand post thread on the Aeropress, you can fool this system - purposefully create under extracted brews to prove a point by not pressing all of the coffee out, or as the inventor of the device was trying to say, count ALL of the water in the puck as "coffee" and overstate the extraction to prove a point (that the Aeropress doesn't underextract, which it most certainly does when brewed according to directions).
andys Said:
We know that the trapped liquid's composition will vary tremendously depending on the brew method. For cupping brews (where the grounds are gently spooned out of the cup), the trapped liquid will be almost identical to the liquid beverage. For full immersion style brews like french press or aeropress, the trapped liquid will be similar (but not identical) to the extracted beverage. In percolation style brews like pourover or espresso, it will be much, much weaker.* Exactly HOW much weaker depends on the brew ratio. Every brew method has a slightly different effect on this, and accounting for it will drive you crazy.
So I think it makes the art and science of coffee extraction far more complicated -- and due to all the ambiguities, ultimately less useful -- if we try and include the trapped liquid in our measurement process.
Immersion methods (including the Aeropress and vacpot) are much less prone to pulling that last bit out differently than the first bit. The end of extraction and grounds separation are pretty quick.
Wash methods (like drip, pourover, and even espresso), the extraction rate is changing AS you receive the end product. And you're absolutely right, the last bit will be weaker than the first bit, and will taste dramatically different for wash methods.
I, my wife, and anyone I've done presses for (normal ones, 2.5% strength, diluted to normal strength) cannot distinguish whether I press that last bit out or not - so even if that last bit is slightly different in composition, it doesn't affect the end product. Look at the various AP championships and whether they fastidiously stop pressing at the first sign of air or not is a variable that doesn't determine a winner or loser, so it's at best a tertiary variable.
That's the beauty of the subtlety of coffee - each brew method has a different extraction rate and method of obtaining the final brew. Investigating these things leads to serendipitous findings. For example, one thing I've kept seeing with the Aeropress lead me to another discovery with the press pot - higher brew ratios help protect against over extraction. I haven't posted the results because I'm not done with it yet, but I have had issues with a press pot and overextraction - but increase the brew ratio and dilute the result with clean hot water and it produces a lovely bright coffee on par with an AeroPress. Who knew?
andys Said:
The gold standard of extraction measurement has always been comparing the mass of solids found in the evaporated beverage to the original mass of dry coffee. Although not a perfect method for every brew style, it is simple, repeatable, and gives a reasonable correlation to taste. The interesting thing is that when we use this classic, imperfect extraction measurement protocol, people's taste preference usually centers around 19% -- no matter what brew method is used.
*For example, the last bit of espresso that flows into your cup might be only 15% as strong as the first bit. The last bit of pourover coffee is also much weaker than the first.
I find closer to 20% but we're in the same exact ballpark. Absolutely agree that the gold standard of extraction is determining the TDS in the cup and ratio to original coffee.
For methods that the end extraction and coffee absorption are stable (espresso is drier by my experience than drip brew and pourover with proper grind - and may be why espresso may prefer 19% and the old SCAA standards are based on drip methods of final strength coffee) this works very well. Vacpots fall into this category too - they seem very consistent for coffee absorption.
But press pots and AeroPresses vary widely on absorption. If you do a press pot (not AP) of 750g water and 43g of coffee, and COULD yield 700g of coffee beverage, but leave that silty bit of grounds at the bottom because the press screen doesn't go all the way to the bottom and you only get 600g total out of your presspot with a bunch of really wet grounds at the bottom, you'll falsely think your extraction is lower than it really is. And what's the end result in the bottom made of? Overextracted coffee? same stuff?
Such are the mysteries of coffee, and they demand answers! 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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