Posted Fri Aug 17, 2012, 4:34am Subject: Understanding Infusion/Steep
I'm still in the middle of several runs but am finding an interesting phenomenon with steeping (aka immersion, full contact, infusion... basically Mason Jar/French Press/CCD/Cupping brewing methods).
These type of brews will approach an equilibrium point - the strength as a function of time is linear with the natural log of time, over an infusion of about 12 minutes.
While this seems inconsequential, it's actually quite important. This implies that once you set the brew up (grind, brew ratio), unless you stop the infusion early, it will reach stability and it essentially won't matter how much longer you steep.
This also implies that if the grind is coarse enough, you won't get "overextraction", even if calculated by an immersion calculation.
This explains why cupping can result in good-tasting coffee even if allowed to cool to room temperature over a half hour.
More to come...
(btw - I'm using very small sample drops to check strength - this seems to be sufficiently close to my other method of making and terminating brews at specific intervals - provided the brew slurry is large enough that a drop or two of solution doesn't make huge changes in the total mass. There isn't enough sample to run through a syringe filter, and there is more variation in the refractometer reading than normal, but the time savings is worth it - I can increase the data density in much less time).
------------------------------------------ ----------------------------------------- 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
redkiosk Senior Member Joined: 13 May 2012 Posts: 156 Location: Chicago Metro Area Expertise: I love coffee
Espresso: Illy Francis-Francis X1 Grinder: Baratza Preciso w/ Esatto... Vac Pot: Someday, very intriguing Drip: Bunn Trifecta MB Roaster: A sure path to divorce!
Posted Fri Aug 17, 2012, 8:36am Subject: Re: Understanding Infusion/Steep
Netphilosopher,
I'm fairly new here and make a point of reading your posts (many times 2-3 times over so I fully understand it). Kevin needs to have you do a workshop at CoffeeCon next year. I for one would be highly interested in your discussions on coffee brewing methods. Thanks for taking the time to post here. Take care!
Jim
The pathologically precise are annoying, but right!
Posted Fri Aug 17, 2012, 9:55am Subject: Re: Understanding Infusion/Steep
redkiosk Said:
Netphilosopher,
I'm fairly new here and make a point of reading your posts (many times 2-3 times over so I fully understand it). Kevin needs to have you do a workshop at CoffeeCon next year. I for one would be highly interested in your discussions on coffee brewing methods. Thanks for taking the time to post here. Take care!
Ha! Funny. I'm just a home-based interested geek. I just chose this as my hobby because I'm allergic to beer, wine takes too long and the raw material supply is so variable and not as ubiquitous as coffee, and my other hobbies are much more expensive! LOL
A friend of mine called me a "coffee hacker". Same friend that I was thinking of working with to build a home-made scanning electron microscope... until we found out someone has already done it.
...I've also been recently accused of suffering from hypergraphia - but I assure you I'm not bipolar. My posts are long because when I post short ones, I get accused of leaving details out!
<shrug> Can't win.
------------------------------------------ ----------------------------------------- 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 Thu Aug 30, 2012, 5:51am Subject: Re: Understanding Infusion/Steep
I just came across something interesting - now repeated it.
I was brewing with a fairly coarse grind with the AeroPress, and just doing some sense checks on series of termination brews vs. sampling throughout the steep period.
In the process, I found a couple of times where the strength of the coffee IN THE GROUNDS was slightly higher than the stuff in the cup after brewing.
I thought it was a fluke, but I've been able to reproduce this at least once.
It reminded me of AndyS' checks, where he was finding the strength of an AeroPress in four different presses were similar, but curiously the strength was stronger for the last 3 of 4 presses: "Re: coffee refractometer"
For an example of a typical series of brews: "Re: Coffee Extraction Discussion, Questions for the membership:" (shown is Brew Ratio 7.5%, which is the Coffee Brew Ratio - for calculation ease, I've moved to Water Brew Ratio, which I call "R" for algebraic ease, or the ratio of Brew Water to Brew Coffee. B or BR = 7.5% is equal in brew recipe to R=13.33, or 13.33grams brew water per gram of coffee). Also note that the time scale is when the press was started, not at the end of the press.
I've done very coarse grind in a press pot, checking strength of the coffee and then pouring all of the slurry into a brew basket, but recently I did a normal press pot, leaving the grounds in the bottom when I decanted the coffee from the pot.
When I went back and just for fun checked the strength of the wet grounds - it was REALLY high. I think I'm understanding that the extraction still continued in the wet grounds, but at a very concentrated effective brew ratio - so even an extra half percent extraction means a large change in the few grams of solution still in the wet grounds.
So, I think what I might be seeing is for the earlier terminated brews (using the example plot), the brew water is still dissolving coffee while the press is occurring. In other words, the extraction is still climbing the solvation curve while I'm pressing, but while I'm pressing the remaining solution is pushing the brew ratio stronger - and the resulting strength is significantly higher for anything left in the grounds.
In the example - termininating the brew at 60 seconds means a cup at 1.25% strength - but if it takes another 30 seconds to press, the extraction is slowing but not stopped, but the solvent available is being reduced, so anything that dissolves when the press is started is going into a smaller and smaller amount of solution. If the press takes until 1:30 to complete, according to the chart you might think the grounds would be at ~1.35% strength - yet in practice the grounds strength may be 1.55% or more.
Additionally, if you wait some more time before sampling the grounds for an early brew termination, the strength may even be higher - very small amount of solution in the grounds, it takes miniscule amounts of TDS to change the strength of the solution in the grounds.
This phenomenon is less apparent as the time is increased - at 12 minutes, it doesn't seem to matter if you sample the grounds immediately after or another 5 minutes later, it's still within measurement error the same strength as the produced coffee.
This also seems to show up with a probe check on CCD - I did a medium grind on the CCD, starting the drip at 1:30. It took about 70 seconds to complete the drip - and I caught a few drops of the last of the drips at 70 seconds. These were higher in strength than the coffee in the cup - and according to previous data this would have been on the rising portion of the extraction curve.
So, I did same grind, but started the drip at 6:30 - still took about 70-80 seconds for the drip, but this time the strength of the last few drips were basically the same as the strength in the cup (and stronger than the 1:30 terminated brew).
Just more interesting observations as the poking around continues.
------------------------------------------ ----------------------------------------- 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 Thu Aug 30, 2012, 5:52am Subject: Re: Understanding Infusion/Steep
Sorry - double posted.
------------------------------------------ ----------------------------------------- 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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