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 Sun Jun 3, 2012, 4:00pm Subject: Re: Calling All VST Refractometer Owners - A Brewing Challenge:
andys Said:
...Have you tried a dark roast? Starbucks might have just what you need. I think it is fairly easy to get extraction numbers much higher with a dark roast compared to your typical bleeding edge light roast.
Andy, do you have a sense how much of this difference might be explained simply by lower moisture content - therefore lower relative mass - possibly in dark roasts? I can remember a couple very dark roasts where, given the same measure in grams, the volume of the beans is noticably greater than lighter roasts.
If the heavy roasting bakes out more water, there is actually more "coffee matter" per gram of some dark versus light roasts. If true, then using a given mass of such a dark roast would essentially mean you're using more coffee matter and therefore the extraction ratio could be higher for that reason alone - with less or even nothing to do with true extraction characteristics themselves.
Posted Sun Jun 3, 2012, 8:21pm Subject: Re: Calling All VST Refractometer Owners - A Brewing Challenge:
TonyVan Said:
Andy, do you have a sense how much of this difference might be explained simply by lower moisture content - therefore lower relative mass - possibly in dark roasts? I can remember a couple very dark roasts where, given the same measure in grams, the volume of the beans is noticably greater than lighter roasts.
If the heavy roasting bakes out more water, there is actually more "coffee matter" per gram of some dark versus light roasts. If true, then using a given mass of such a dark roast would essentially mean you're using more coffee matter and therefore the extraction ratio could be higher for that reason alone - with less or even nothing to do with true extraction characteristics themselves.
I believe the moisture content of roasted beans is quite low -- two or three percent for medium-roasted beans, according to Illy.
If medium roasts contain 2.5% moisture, and dark roasts 1.5% moisture (just making up possible numbers), that difference would produce very little change in the computed extraction yields. I once asked Vince if any of the previous coffee scientists (such as Lockhart) had felt it necessary to compensate for bean moisture content. To his knowledge, they had not.
Posted Mon Jun 4, 2012, 5:55am Subject: Re: Calling All VST Refractometer Owners - A Brewing Challenge:
GlennV Said:
...What I don't understand, though, is how this squares with the fact that those with far more tasting experience than me are recommending 19-20% yields for both drip and immersion methods, with the usual formulae. For example, the Nick Cho video on youtube showing his clever dripper technique would come out at about 22% yield using all the brew water for the calculation ("Gold + Paper + Clever", which is certainly a full immersion technique as he pulls the grinds out of the brew in a Gold filter before the drawdown).
Such is the problem with "rules of thumb" and subjective evaluations. Confirmation bias in subjective rating is a VERY real thing. If you taste something, develop an opinion, and then an instrument tells you that you may be wrong, your subjective opinion will change. We're all human.
I deal with it in my day job too.
I've got my own clever dripper coming, but using the basket from my BCM-4C as a makeshift immersion dripper, I don't expect this to change.
What I'm finding is that heavier extracted IMMERSION brews are not bad. Suppression of brightness, sure, but body gets pretty rich and it can actually sweeten up some. It starts to get hairy when you start pushing more than 22.5% (for me, of course - taste of coffee is a very subjective thing).
Ever had unsweetened Turkish coffee? That should be boiled to crap, but I think if it's properly prepared it won't be bad at all. It's just fine coffee in a very high brew ratio that's really only brought to brewing temps for maybe 1-2 minutes.
I've had good, old fashioned stovetop percolator-produced coffee that I wasn't supposed to like, but surprise! Really nice and rich. Try it (if you can find it) in Breckenridge or other hi-elevation. The percolation recycling happens at 190°F for the whole cycle. I didn't have my VST at that time, but I do remember (since it was earlier in my coffee journey) thinking that according to all sources it should be crap coffee.
I think that the percolation (or wash if under pressure) method is more "thorough", or more efficient. So, at the end of the brew cycle for percolation (or espresso), you've washed out the good stuff and it steps over into over extracted very quickly. It doesn't take much of the end-brewed stuff to ruin a batch of coffee.
In immersion brewing, the increasing saturation of the solution seems to act as a buffer against severe overextraction - but you can still get elements of it, it just won't be crazy bitter.
Regarding moisture content, I've been thinking about that - and looking at the loose density of various roasts that I've done, there's probably a small effect here. Coffee roasters (like Starbucks) know this - darker roasted coffee in a package occupies more space per lb than lighter roasted. Some of this difference has to be moisture, but really the majority of this is the changes in density of the beans themselves. Converted lignin and cellulose to carbon (much lighter) with darker roasts, etc. There's also a compelling argument that any changes to the amount of coffee matter is displaced by the fairly inactive carbon (pre-combustion charcoal, essentially).
However, by the math, it is pretty small. If you use 25g:245g (coffee:brew water) for two brews, and one is actually 1.5% less moisture (i.e. the "coffee matter" is actually about 1.5% more), and you extract them both to 20%, the difference in strength is only about 0.02% on ~2% strength - within variation/discretion of the refractometer.
4.6% - that's pretty strong, about the limit of what I've been able to get.
------------------------------------------ ----------------------------------------- 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 Aug 17, 2012, 8:27pm Subject: Re: Calling All VST Refractometer Owners - A Brewing Challenge:
So, not surprisingly, I did know the answer all along.
People are really shy sometimes, aren't they?
For my BCM-4C: E = S (R - A)
Extraction = strength * (water brew ratio - absorption)
For infusion methods:
E = (S R) / (1-S)
Extraction for immersion methods = (strength * water brew ratio) / (1 - Strength)
yep, you can invert these. 18% Coffee Brew Ratio means R = 5.56 (that's grams of water per gram of coffee)
S = E / (R + E) for infusion (Press Pot).
For my BCM-4C, it's S = E / (R - A), where A = 1.7 for my brewer.
Assume that the maximum extraction on any coffee is 30%:
If in a drip machine: S (30% extraction) = .3 / (5.56 - 1.7) = 7.77% strength.
But for infusion: S (30% extraction) = .3 / (5.56 + .3) = 5.11% strength.
The most I've been able to do in my press pot with VERY fine grind was about 4.5% strength at this brew ratio, meaning a roasty extraction of a bit more than 26%.
There's the most compelling argument for the difference between brewing methods. There's a physical limit to the brew strength unless you're washing out the coffee with fresh, lower concentrate brew water.
And for me, that brew tasted like A$zz! LOL
I keep going back to the rinsing salt out of a pair of jeans analogy.
Method 1) Take a pair of dried jeans with salt in them. Wash the salt out of them - but you only have a 5 gallon pail of water to do all of the rinsing. You take the jeans, put them in a colander, slowly pour clean water over the jeans and allow the water to soak and drain away from the jeans, dissolving out the salt, until the bucket of water is empty. This is like a drip method of brewing coffee.
Method 2) take that pair of dried jeans with salt in them. This time, you just put the jeans in the bucket - then allow them to soak, occasionally stirring them around or even agitating them. At the end, you pour the jeans and the salty water into the colander and allow to drain. This is basically like infusion method. If, instead, you push these jeans to the bottom of the bucket while they are soaking, and then drain off the rest of the water - you'll have a press pot analogy. If you take the jeans, put them into a colander, and then press them into the colander - this is analogous to an AeroPress.
It's obvious that method 2 will have more salt in the jeans, even if pressing them, vs. method 1.
------------------------------------------ ----------------------------------------- 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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