Posted Sat Mar 10, 2012, 11:30am Subject: Re: coffee refractometer
TonyVan Said:
Andy, putting two and two together with your earlier comment in this thread about extraction envy with the K10 vs. Robur, was this 0.5% difference from the tamper size the explanation for the 0.5% delta that you had originally attributed to the grinders?
No, that side-by-side K10 vs Robur comparison was using same coffee, basket, tamper, espresso machine, water, etc. I can only speculate that the particular K10 in question delivered a little less fines than the Robur.
TonyVan Said:
One of your posts last fall on this difference triggered a virtual stampede on 58.4mm tampers
Posted Sat Mar 10, 2012, 4:59pm Subject: Re: coffee refractometer
AndyS - yep, the third filter was actually a double+ filter. It captured a little bit of fines but really clarified the coffee. The + means I cut a melitta cone filter material as a final filter AFTER two stock AP filter discs. Did the job, but was a BEEEOAAAHHHHTTCHH to press... 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
TonyVan Senior Member Joined: 24 May 2010 Posts: 269 Location: Pacific Northwest Expertise: I love coffee
Espresso: GS/3, La Pavoni Grinder: Macap M7K, Rocky Drip: Kone
Posted Sat Mar 10, 2012, 5:09pm Subject: Re: coffee refractometer
One more question, Andy. From your February 23 post in this thread:
andys Said:
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.
It's always been my (possibly mistaken) impression that "fines-is-fines" and their mean and median size within the fines portion of the typical (bimodal) distribution curve was essentially unaffected by grinder's adjustments (within the espresso range).
If so, then the "extra-fine fines" that might theoretically be generated by slightly tighter grinding (at least within your context here of moderately under-dosing a basket) probably don't really occur. This appears to be borne out in your conclusion that you don't notice silty espresso.
I think what you're saying is that you're confident your evaporation results are correct and they don't agree with the instrument. If that's the case, then you certainly should contact Vince at VST.
Posted Sat Mar 10, 2012, 5:26pm Subject: Re: coffee refractometer
Ok, the Abstract:
After several subjective taste tests, (press pot, pre-heated water in BCM-4, and Aeropress brews, as well as running myself out of coffee and one sleepless jittery night...), along with as thorough a test as I can get, I can conclude my VST reads consistently low by a factor of 1/1.17.
Initially used the dehydration method to break down the initial brew and backcalculate TDS and extraction. TDS recovery was a surprising 100%. Method to follow in post.
Then, using the recovered TDS to make a solution, I used known strength solution to confirm my findings. I don't know if re-calibrating the span with calibration solutions would help, but since I know the offset now, I doubt I'll mess with it.
------------------------------------------ ----------------------------------------- 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 Mar 10, 2012, 5:28pm Subject: Re: coffee refractometer
Great minds think alike AndyS - I then did a pre-heated press pot with 6:00 steep time at normal strength brew ratio (700g to 40g). This produced a strong coffee that required several filterings but approximately 655g of initial coffee beverage (actual 657.1 which was found to have fines of ~2.1g). This was VERY strong, with much bitterness and creosote. OBVIOUSLY overextracted, but the VST called it near perfect at 1.23% average. However, 1.23% * 1.17 is MUCH closer by taste - strength of 1.44-1.45%. The VST measurement implies a back-calculated extraction of 20.17%, but by experience I know this is pushing 23-24% extraction. (one of my test brews is using 40g of coffee in a press-pot, then filtering the results to obtain the undissolved fines, then checking the remaining dehydrated grounds - every 0.1g is 0.25% change in 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 Mar 10, 2012, 6:05pm Subject: Re: coffee refractometer
Initial brew and Deyhdration:
22g Coffee 232.1g brew water
199.6g Produced Coffee 1.95% TDS (VST measurement)
49.3g Wet Puck of Spent Grounds, Wet (into oven for dehydration) 185.5g Coffee Sample (into oven for dehydration) (Coffee lost during sampling = 14.1g)
2.264% / 1.95% = 1.161 (or stated more accurately, actual is 16% higher than VST reading)
------------------------------------------ ----------------------------------------- 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 Mar 10, 2012, 6:18pm Subject: Re: coffee refractometer
To test this, I scraped out the dry TDS from my bowl, and took 2.0g of the scraped out TDS, added to 101.3g of total mass with hot water. This produced a strong coffee-esque beverage that is somewhat reminiscent of instant coffee – if were boiled again and again. LOL
When it evaporated to around 100g, I took samples of what is as best as I can get a known 2.0% strength coffee. Recalibrated, and measured with the VST – and achieved a range of 1.70-1.73%, call it 1.71%.
So, further interested, I took 50g of this "rehydrated" coffee at supposed to be 2.0% but measures 1.71% strength, and diluted that to 100g again. This now should be 1.0% strength – and managed to achieve a VST strength of 0.86 (range 0.84 to 0.87).
Honestly, I don't know where to go from here, but I'm more than convinced that this is simply off by a factor of 1.17. The device is remarkable in the craftsmanship, and it is consistent as best as I've ever seen. Now that I'm aware of the offset (and YOUR MILEAGE WILL VARY!!!), I can account for it and continue my journey.
BTW - reconstituted coffee TDS is not good tasting. Perfect example of correctly extracted, appropriate strength, complete crap for taste! ROFLOL!
(Click for larger image)
------------------------------------------ ----------------------------------------- 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 Mar 10, 2012, 6:47pm Subject: Re: coffee refractometer
GlennV Said:
Have you tried repeatability when making multiple measurements of the same coffee interspersed with measurements of water? It may be doing some sort of averaging. In fact, I've just checked the VST website and it explicitly states that it automatically averages multiple readings.
Looking forward to seeing your dehydration results. As I pointed out a couple of pages back, at those sort of concentrations the VST calibration will report a TDS about 6% lower than the anecdotal "0.85 x Brix" that some people are reported to have used in the past.
Yes, absolutely. If it's doing a run-to-run average, I don't see it, nor would I want a machine that did such a thing. It doesn't know if I'm checking 6 different cuppings, for example - if it averaged these readings I'd be hotfired pi$$ed.
I have also made multiple measurements while re-zeroing with distilled water between them (though this seems excessive). It's quite repeatable. Just off a bit.
------------------------------------------ ----------------------------------------- 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 Mar 10, 2012, 9:18pm Subject: Re: coffee refractometer
aye aye aye... decided to drag out my centrifuge. Aeropress fines are minimal, so no longer worried. Additionally, the difference in reading between Aeropress filter and centrifuged coffee are not detectable - so I got that goin' for me.
Decided to run the original Aeropress recipe. This is an underextracting recipe - the whole shebang, 175°F brew water, 10 second steep time, "verted" (as opposed to INverted), the works. It's a brew I've done about a half dozen times fully dehydrated (that's both the coffee beverage and the grounds) and another nearly dozen times with dehydrated grounds only.
I used to use "two scoops" at 26-29g, but have standardized to 28.0g for ease. The AP original recipe produces a reliably underextracted 14% to no more than 15.75% extraction, and a very low absorption ratio of 1.05-1.10 times the original mass of coffee. This is presumably because the contact time is so short, the cellulose of the grounds do not have time to really soak up much water (or coffee, or whatever). The resulting back calculated strength is also pretty reliable at somewhere around 5.5% to 6%, and the dried grounds range from 23.7g to 24.1g.
So, I went ahead and made a brew. Actually, I made two. I needed some for centrifuging, and I needed some for range testing of the VST.
And yes, you saw that right - where I was expecting 5.5-6% strength (the same range I've duplicated in multiple brews) I measured only 4.95% with the VST. Using my 1.17 factor, I expect a more normal strength of 5.8% or 5.9% with dried grounds around 24g (grounds in the oven now). The VST back calculation would be a dried grounds expected value of 24.6g - something I have NEVER achieved.
VST back calculated extraction is only 12.1%! Obviously, if people are following the original recipe, there is no way they are drinking coffee that's only 12.1% extracted.
The second brew is not much better, 4.98% (I ran the second brew through a slightly warm AP), the one used for the centrifuge check - basically, the AP filter is plenty fine for these measurements - or at least they are not the reason I'm getting readings this far off.
Stay tuned, coffee fans!
------------------------------------------ ----------------------------------------- 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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