Posted Mon May 14, 2012, 10:45am Subject: Re: Coffee Extraction Discussion, Questions for the membership:
What's really puzzling is when I can have the same brew ratio (say 10%)for two different methods, and obtain two different strengths.
Make it in the 4 cup drip pot and get a strength of 2.75% and it tastes CLEARLY overextracted, even when diluted to 1.3% strength.
Make the same coffee, same brew ratio in the Aeropress, trying to over extract, and best I seem to be able to get is 2.18 or 2.21% strength - diluted down to 1.2-1.3% strength, it tastes clearly overextracted, yet the all the back calculations are saying it's on the "low" side of extraction.
the latter was 200g water : 20g coffee, D-3 grind and 5:00 contact, yield in the cup 176.3g at 2.18% strength. Yield based back calculates to 19.3% extraction, but no way. It tastes overextracted.
The drip pot: 40g coffee, 415g brew water (added 15 for evaporation), 328.1g produced at 2.75%. Yield based extraction back calculates to 22.5%, and is in line with how it tastes (over extracted). The spent coffee weighed 112.3g (so the absorption was around 1.808).
Please, feel free to check my math - but I've been over this several times. I also know what overextracted tastes like, and both of these are definitely in the same class of fairly bitter, wince-inducing. Yet I can produce a decent cup of coffee by adjusting the grind to more normal. Then, I get "severely" underextracted Aeropress that tastes just fine - and it's not like I "love" underextracted coffee. LOL
Just more curious observations that are taking some time to gel.
------------------------------------------ ----------------------------------------- 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
Chang94598 Senior Member Joined: 24 Oct 2007 Posts: 207 Location: SF Bay Area
Posted Mon May 14, 2012, 10:54am Subject: Re: Coffee Extraction Discussion, Questions for the membership:
My understanding for the brew formula is:
Strength= (Coffee*Extraction%) / (Total Water - Total Water * Absorption)
Dr Lockhart from the Coffee Brewing Institute used 2.086 ml of water absorbed per gram of dry coffee. In my experience of brewing single cup drip and Abid, the absorption rate is about 2.25 g (not ml) per gram of dry coffee.
The ground coffee water absorption is time and water quality dependent. Coffee will retain more softer or distilled water, and vice versa. In drip, it also varies if the paper is pre-wet or not (duh, obviously).
The decision to use volume vs weight is size. I assume in commercial settings, where large amount of coffee is needed, volume is easier. In home setting, weight is convenient. It is only a matter of molality vs molarity, just like in a chemistry lab.
No, this is the formula that the brew control chart uses. I'm just re-vamping my terminology to fit this model, therefore I don't have to add any more complexity than I need. I used to define absorption as the calculated amount of WATER in the spent grounds, but I'm also starting to see there's some differences to how this is applied. Also, the brew charts are predicated upon an assumed absorption, or extraction is defined as Total Dissolved Solids / coffee produced.
I'm gradually understanding how this is coming together, and have a handful of more brews before I can summarize what I think. The concept of "absorption" is interesting - both in how it's used to predict the amount of coffee beverage from a given amount of brew water and dry coffee, and how it plays into "extraction."
Gimme a few days to sort out some crosschecks, and I think I can simplify all of this. I've also got to dig out my Press Pot and do some trial brews with that as well, but I see there's a reason why the thinking works.
From the simple concept of: Coffee Produced = Brew Water - (Absorption X Coffee)
and defining Brew Ratio = Coffee/Brew Water Strength = TDSg/Coffee Produced, or TDSg=Coffee Produced X Strength, (Strength aka %TDS) and Extraction = TDSg/Coffee
To translate the brew charts to mass-based from hot brew water volume-based, Absorption should be approximately 1.76
So far, this seems to work for auto drip and pourover.
In every case, however, the ONLY indicator that you have "extraction" right is by taste.
------------------------------------------ ----------------------------------------- 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: 394 Location: California Expertise: I like coffee
Grinder: Kyocera CM-50 Vac Pot: S/S Moka Pot Drip: Aeropress
Posted Mon May 14, 2012, 12:35pm Subject: Re: Coffee Extraction Discussion, Questions for the membership:
Netphilosopher Said:
The drip pot: 40g coffee, 415g brew water (added 15 for evaporation), 328.1g produced at 2.75%. Yield based extraction back calculates to 22.5%, and is in line with how it tastes (over extracted). The spent coffee weighed 112.3g (so the absorption was around 1.808).
I think the most likely explanation is that the liquid retained in the wash through method is much weaker in dissolved solids than that of the immersion method.
Suppose that the retained liquid is of strength 0% for the filter brew and is equal to the strength in the cup of the Aeropress brew. If you could somehow wash out those retained dissolved solids the extraction yields of the two brews would be nearly identical.
Coffee Produced = Brew Water - (Absorption X I.D. Coffee)
If I am using 100g of brew water, 6 grams of coffee, (6% brew ratio) I expect the coffee produced to be 100 - ((abs=2) * (I.D.Coffee=6)), or 88 grams.
Conversely, if I want to know how much coffee to use to produce 88g of beverage at 1.37% strength at 20% extraction, I use 88*.0137 ~ 1.2g, 1.2g/.20 = 6g of coffee.
If I want to know how much water to use, I need at least 88g of water, plus AbsorptionXcoffee (2*6) or 100g of brew water.
The other issue with the coffee produced = BW + (E - A) * DCoff is you have to know the extraction to determine it.
Using 100g BW and 6g coffee, coffee produced = 100 + (.2 - 2)*6g = 89.2, but then you'd need to also apply the extraction to determine the converted absorption. Now you have to bring this combined term everywhere you carry "absorption".
Substitute brew ratio and strength (to make the terms dimensionless) and it is not nearly as clean.
Again - look at any of the SCAA or SCAE gold cup literature - the definition of absorption is pretty clear - the math is easier for me to remember, too. It's usually generalized as "each gram of coffee absorbs 2g or 2ml of brew water".
Like I said before, I was starting with re-constituting the old brew charts first - and this seems to be how they did it.
You're right, it's only a constant - except when it isn't. What I'm finding out is what you've already stated - the stuff stuck back in the spent grounds is a different character depending on the brew method. So there's a difference between predicting the coffee produced and also the extraction of said coffee. It's why I started the 3X3 experiment, and asked the question that started this thread:
"What happens when you have a technical extraction of 16% when it TASTES like an extraction of 24%?" This is not a trivial disconnect - and it isn't my imagination.
It also provides me with major clues as to why I've not been able to use the AP to produce a "technically overextracted" brew.
------------------------------------------ ----------------------------------------- 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
It's inconsistent in the same way that 100+1=100 is. It's an approximation, albeit a pretty good one for normal conditions. Outside that range it diverges somewhat more. Isn't one of your goals to improve the predictive power of these formulas/charts? If it were me I would make approximations after I got there, not before.
But this isn't the interesting part of your question.
<sigh> How are you going to explain that to Lord Kelvin?
Meanwhile, I'm expecting that you're going to put together some kind of Unified Field Theory of Coffee Extraction. On one end of the extraction spectrum you'll have espresso and pourover brews, where the liquid trapped in the grounds at the end is weak enough (the Weak Force) to be ignored. On the other end you'll have cupping, Eva Solo and perhaps French Press, where the liquid trapped in the grounds is approximately the same strength (the Strong Force) as the beverage, and will be counted in the extraction. Other methods, such as vac pot and Aeropress will fall in specific intermediate areas. They each will have their own Cosmic Coffee Constant that will offset their measurements relative to the others. In the end, 19% extraction will taste about the best for all methods.
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