CoffeeGuy123 Junior Member Joined: 27 Feb 2013 Posts: 5 Location: Pullman Expertise: Just starting
Posted Wed Feb 27, 2013, 3:11pm Subject: Science Behind The Press
I have a Bodum French press and I want to buy a sieve to sift my grounds so I actually have coarse grounds and no fines. What size coffee grounds should I aim for? These sieves are quite a bit of money so I would only like to buy one.
I have heard that 850 microns or a #20 sieve does the job. But would I be able to go smaller? Rather have a coarse grounds then fines in my coffee.
Posted Wed Feb 27, 2013, 7:56pm Subject: Re: Science Behind The Press
I've got a #20 and think it's a little too aggressive (see here, for example). Looks like Nick Cho's been playing with a #50 lately (link). Maybe try his way or split the difference? You can find good deals on gently used sieves on eBay if you're patient.
Posted Wed Feb 27, 2013, 8:18pm Subject: Re: Science Behind The Press
Dear 123, Pardon my butting in. Even though you have a Bodum, if you want to cut the sludge, it would make more economic sense to buy an Espro French Press than an expensive sieve. You could always experiment with a sieve if you happened upon it cheaply on ebay. The sieve that you would buy could conceivably be used for pourover as well as FP, and not appropriate for espresso grind, but why not spend much less money to get a double-filtered FP unit?
So then comes the question: how much fines are required (that overextract) before you can actually taste it?
A little bit of fines and sludge won't matter to taste - the amount that they will overextract is so small that you won't taste it, especially in an immersion method brew like a French Press. The fines do change the average grind size, so overall it's the same thing as having a finer grind (meaning extraction will be higher). When you take a particular grind, then sift out the fines, you're essentially setting the grind coarser.
Try doing an immersion brew of just the fines - yes, it will take a lot of sifting to produce 55g of talc-like brew coffee (to combine with about 880g of water like in an 8Cup Bodum French Press). It won't go all the way to 28%-30% extraction, it reaches equilibrium around 25-26% extraction, depending on the source of the brew coffee. (grinding at 0 setting on a LIDO is pretty much the same thing) It also reaches equilibrium pretty quickly - about 3-4 minutes.
I've done this - hot-brewed in a mason jar, stirred several times, and sealed and set the whole shebang on the counter overnight. 8-12 hours later, re-heat and press the results.
I was trying to see how much of this overextracted coffee can be added to normal extracted coffee before I could taste the difference. I concluded that for me, other than the annoyance of the mouthfeel grittiness, the fines produced with even a whirlyblade are not a major player in taste so long as the overall average extraction isn't much above 21%. We also know that the average grind size pretty much determines the strength (and therefore the extraction) on a 4-6 minute immersion brew. So, if the presence of fines doesn't drop the overall average grind size so much that the whole brew overextracts (with immersion calculation), you are basically good to go. Sludge notwithstanding.
Note that this is only for immersion methods - percolation methods differ in significant ways.
1) during solvation/dissolution, percolation methods are being constantly dissolved with fresh water. 2) grind size is interdependent with contact time because of the effect on percolation rate. Therefore, strength is interdependent with grind size, and so is extraction.
Interesting, nevertheless.
123: if you use 850micron sieve, then you'll need to use a full 5 minute steep for the Press Pot.
------------------------------------------ ----------------------------------------- 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
CoffeeGuy123 Junior Member Joined: 27 Feb 2013 Posts: 5 Location: Pullman Expertise: Just starting
Posted Thu Feb 28, 2013, 1:02pm Subject: Re: Science Behind The Press
So I tried using just a mesh cooking strainer to sift my coffee grounds and if I had to compare it to a # sieve it would be a #20 or larger (have some very course grinds now).
But when I went to make my cup of coffee this morning I still had that bitter/silty taste from the fines in there....I also only let the press sit for ~3 min. So either I need to let the grinds steep longer or......what could be causing this off taste?
I was so excited to try my newly sifted grounds only to find that it was a big disappointment!
P.S. This whole experimental thing has me drinking way too much coffee!
So I tried using just a mesh cooking strainer to sift my coffee grounds and if I had to compare it to a # sieve it would be a #20 or larger (have some very course grinds now).
But when I went to make my cup of coffee this morning I still had that bitter/silty taste from the fines in there....I also only let the press sit for ~3 min. So either I need to let the grinds steep longer or......what could be causing this off taste?
I was so excited to try my newly sifted grounds only to find that it was a big disappointment!...
Drop the temperature of your water. Don't let it get above 195°F at your next pot.
Stir during the first minute to make sure the grounds are saturated. Then, insert the screen and just submerge any foamy grounds. Then wait. Do not stir again. In fact, try not to disturb until pressing.
What you're doing at this point is twofold:
1) you're waiting for the grounds particles to waterlog, give up their coffee goodness, and sink. This can take up to 6 minutes for a particle that's 1.5mm or so, and you have a bunch of those. 2) you're also waiting for the fines to settle and sink to the bottom first. At the bottom means less of them will end up in the cup.
When the time for steep is reached, then slowly and gently press. You'll collect the large still-floating particles and some chaff in the screen, and these in turn will catch up to smaller particles, eventually helping to build a mini cake filter.
If you're really patient, then you can do the paper filter re-press that I do. After the screen press, I withdraw the screen, slap a bunn paper filter (usually trimmed off excess paper) onto the screen including around the screen where it contacts the glass. Very effective, because the paper collects even smaller fines immediately, and this in turn eliminates almost all of the traditional sludge that's still in suspension. The downside is too many fines can REALLY increase the press force - so do this with caution, and don't be afraid to pull the screen back out to "clear" the filter if it becomes impossible to press.
I'm pretty sure I outlined this in my recipes thread in my signature.
Good luck, go with what tastes!
------------------------------------------ ----------------------------------------- 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 Feb 28, 2013, 2:17pm Subject: Re: Science Behind The Press
Also, not a lot of people have delved into the "science" of the press pot, but a couple things:
Every brew setup will reach an equilibrium strength. The equilibrium strength is determined by the average size of the ground coffee particles - larger particles mean lower end equilibrium strength. Most of the time this end strength is reached by 12 minutes - or at least 90% of final equilibrium strength is achieved by that time for the range of grind sizes and distribution we typically use.
Equilibrium means that the strength (and by inference the extraction) does not go higher even if left overnight. It isn't strictly "saturated" but it acts like a solution that is saturated.
The time at which the equilibrium strength is reached is dependent on average particle size - so the finer the grind the quicker it reaches equilibrium strength. Turkish grind reaches equilibrium within about a minute or so. 1.5mm average grind - maybe 4-6 minutes.
The time at which the equilibrium strength is reached is also dependent on temperature - lower temperature increases the time.
Furthermore, there's stuff in coffee you don't want to taste that gets extracted if the brew water temp gets above 205°F. Stay below that temp. I've tested this blind, time and time again with my wife and others, and it holds well enough that in my head it's converting from a hypothesis to a theory.
Make sure you aren't using water that is too soft. Don't use distilled water. You need some calcium in the water to react with bitter compounds (which are actually acids) and neutralize them with regard to taste. In a pinch, add some cleaned and crushed/ground eggshells to your brew coffee, this will knock some of the bite out of 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
CoffeeGuy123 Junior Member Joined: 27 Feb 2013 Posts: 5 Location: Pullman Expertise: Just starting
Posted Thu Feb 28, 2013, 5:59pm Subject: Re: Science Behind The Press
Your name speaks for itself, you are the Aristotle of coffee.
I will try your advice you mentioned. I can tell you right now I am doing a few things wrong, biggest is probably the water temp. I just pull it off the stove from a roaring boil straight into the press.
However I think my problem is coming from the fines of the grind. Even though I have sifted the grounds I am still getting the same amount of sludge at the bottom of the cup. And when I say sludge I mean SLUDGE!
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