If you know the brew ratio and measure the resulting strength, you'll be able to see if you are in the optimum range. It's a chart version of the list of strengths and brew ratio in the previous post.
I'll try and plot my experiment on the chart and post them here.
------------------------------------------ ----------------------------------------- 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 Wed May 16, 2012, 12:33pm Subject: Re: Coffee Extraction Discussion, Questions for the membership:
Ok, here's the data with no extraction calculations - just the experiment plus a few interesting brews.
I know it looks like I faked the data, but nothing could be further from the truth - this is the average of the replicated data pairs for the 18 runs. I didn't plot the EXACT brew ratio (it varies by a tenth percent here or there - I might have 18.09% for one of the data points, for example).
I was absolutely floored when I saw how repeatable and linear the data turned out.
(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 Wed May 16, 2012, 12:41pm Subject: Re: Coffee Extraction Discussion, Questions for the membership:
and here's the data with an overlay of the normal (brew chart based) 18% and 22% extraction, and the new modified immersion method of calculating extraction.
I originally got down to it by trying to get the any of the extraction lines to at least follow the brew ratio (assuming the three brew ratios are similar in extraction, which is what they taste like). The only solution is when the absorption equals negative extraction.
Now I've locked in a 7.5% brew ratio, and I'm walking the grind setting up and down to plot out the extraction with the bodum bistro settings and a 3:00 contact time.
Once I get that centered, I plan on checking the sensitivity of contact time given a 19.5% extraction at 3:00 - up to 8:00 contact time.
THEN, I'll play around with lowering the initial brew temperature, but that will be next month at this rate.
(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
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 Wed May 16, 2012, 1:58pm Subject: Re: Coffee Extraction Discussion, Questions for the membership:
So the magic number 2.068 came from fitting the formula to the chart graphic instead of from the literature? I was wondering why there were so many significant digits.
But I was mainly curious about how you arrived at 1.76 when you converted to mass/mass for the brew ratio.
It seems to me there are two possibilities: (1) The strength was originally in units of mass/volume (2) The strength was originally in units of mass/mass
If case (1) were true then the new absorption constant would simply be the old one times the density of water at brew temperature, which itself is a very minor change to the brew chart. The bigger change would be due to the new units: the 20% extraction sweet spot would occur for 57.1 g/kg and 1.30% (instead of 55 g/L and 1.25%).
But I was guessing that case (2) was what you were working with. That is, that the strength was ALREADY in units of mass/mass. With a formula that has nonsensical units what exactly would it mean to change the units of the brew ratio?
So here's a graphic of the chart with your absorption choice of 1.76. The solid lines are the original brew chart lines and the dashed lines are those that correspond to the mass/mass brew ratio with absorption 1.76.
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 Wed May 16, 2012, 2:00pm Subject: Re: Coffee Extraction Discussion, Questions for the membership:
The thing is, it doesn't even matter what the absorption constant is so long as it matches the brew. That's why it's an input parameter in the Mojo software. Except that they use a different definition. Their "water loss" in g/g is basically your absorption constant + 0.2. So if the grounds are absorbing 2.0 g of water per gram of initial grounds then that's approximately the same as your choice of 1.76.
If I were using Mojo for my brewing I would input a lower number as I almost never see anything close to 2g/g of water retained in the grounds.
Posted Wed May 16, 2012, 2:35pm Subject: Re: Coffee Extraction Discussion, Questions for the membership:
jpender Said:
The thing is, it doesn't even matter what the absorption constant is so long as it matches the brew. That's why it's an input parameter in the Mojo software. Except that they use a different definition. Their "water loss" in g/g is basically your absorption constant + 0.2. So if the grounds are absorbing 2.0 g of water per gram of initial grounds then that's approximately the same as your choice of 1.76.
If I were using Mojo for my brewing I would input a lower number as I almost never see anything close to 2g/g of water retained in the grounds.
And it works absolutely fine - for percolation methods. It's basically the yield method, where extraction = (produced coffee * strength)/Coffee.
Falls apart at higher brew ratio and immersion methods. Unfortunately, that's where cold brew and aeropress operate. It happens to be sufficiently close for French Press because it's typical to use a "normal" brew ratio, and it's in the region where the two methods overlap with regard to the extraction, strength, and brew ratio.
In fact, it's really only immersion methods that we need to know the brew ratio.
It's interesting to think of what is happening in the brew basket for a pourover or automatic drip or any of the percolation methods - there's this increase in extraction rate, and then the extraction slows as the coffee coming out of the basket gets really strong at the beginning, then drops in strength. Then, the nasty stuff starts to be extracted - and if you continue to extract even more, that's where it gradually becomes overextracted.
I did do a kool thing this morning. I had a nicely extracted cup of coffee at a 7.5% brew ratio (AeroPress), somewhere around 1.5% strength. Then, I added another ~40g of moderately warm water to the spent grounds in the AP, stirred for a minute, and pressed... some more. Got another 30ish grams of stuff that was around .80% strength - but tasted REALLY GOOD (just weak) by itself. Added to the original cup I was pleased to find a nice, decent cup of coffee, that responded well to a dollop of fresh hot water (end strength around 1.18%).
I like immersion methods - but I can't help thinking of all that good coffee I've left stuck in the spent grounds... 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
in which case, assuming the specific heat capacity of ground coffee is 0.4 that of water (as in Scott Rao's book), the initial average slurry temperature of your 18% brew would have been over 3C lower than your 6% one. For example, if your water temperature was 95C and the dry grounds temperature 20C, and assuming no heat transfer into the plastic ...
Before you get to the stage where you can't face grinding another bean, might I suggest trying a protocol where you add the first 75g of water to the 6% brew at the same temperature as the water added in the 18% brew, so the hit temperature is the same, and then the rest of the 225g at a lower temperature in an attempt to equalize the initial slurry temp? Nevertheless, impressive stuff.
The apparent linearity of these results could be a coincidence.
If higher brew ratios (lower temperature profiles) result in lower effective extraction AND the grounds liquid is actually something less than full strength coffee then you could get a result that looks like the grounds liquid is full strength when it isn't.
For example, if the brew ratios are 6%, 12%, and 18% and the strengths are 1.3%, 2.6%, and 3.9% it looks like the grounds liquid strength equals the cup strength. That would imply an effective extraction (all the liquid) of 21.7% for each of the three brews. They might taste "okay".
But what if the strength of the grounds were actually only 50% of the cup strength? Then the effective extractions would be 20.8%, 19.8%, and 19.0%. These might all taste okay too.
The problem is that we don't know if our lone taster can reliably resolve differences of this magnitude. If he can only say "underextracted", "okay", "overextracted" with certainty it leaves a fair amount of wiggle room.
I'm not sure that your presciption for adjusting the temperature makes sense. I've spent a little time recording Aeropress temperature profiles and the concept of a "hit" temperature as a way to guarantee equal extraction profiles seems like a reach to me.
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