Chemex: why you should hate it

press, drip, syphon, clover

Re: Chemex: why you should hate it

Postby barrett on Mon Feb 23, 2009 12:56 pm

amber fox wrote:anyway, in thinking about pourover brewing recently, i was wishing for a zero-gravity chamber, in which i could suspend the coffee particles for an immersion period, during which all particles would be evenly extracted. This would ideally finish with a quick flush through a fine cloth or pre-rinsed beached paper filter, with minimal further agitation (and potential for overextraction of some grounds that would receive more agitation than others).

NASA have any extra funding? maybe Google would be a better bet.


Brewing without gravity would pose a whole new set of issues - like how to control water that's trying to go everywhere.
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Re: Chemex: don't hate it, embrace it

Postby Scott Rao on Mon Feb 23, 2009 5:24 pm

Andy, somehow I didn't see your post til now. Glad you chimed in again.

Andy Schecter wrote:What's interesting about this passage is that the extraction pattern outlined in the book for espresso is the opposite of the extraction pattern you say that the Chemex produces.

Thinking about this, it seems possible that when a Chemex pot leaves the grounds near the top high and dry, it's a good thing: these grounds don't get overextracted as the upper layers might be in a typical espresso extraction.


Andy, I think it is quite unlikely the high-and-dry grounds is a good thing. The difference is that espresso is a top-down-only extraction. The pressure gradient ensures that the flow of water is very much top-to-bottom (for those of you not familiar with this concept, instead of an espresso machine pumping pressurized water onto the grounds, imagine there is an incredibly strong vacuum sucking the espresso from the bottom of a naked portafilter. That is essentially what the grounds and water in the basket feel due to the pressure gradient), with no slurry of stuff mixing around, and certainly no opportunity to stir or alter the flow patterns.

In Chemex and other drip brewing (I'm just going to call all automatic and manual gravity-powered percolation methods drip for this post) methods, on the other hand, the water may enter the top and exit the bottom, but what happens in between is quite different. Unless you were to use extemely coarse, very old grounds (i.e. no gas to create turbulence) the water will dwell in the slurry for some time. The slurry is also turbulent because the water from the sprayhead or pouring vessel agitates the slurry. Because of this turbulent-slurry effect, the water is not just going straight from top to bottom and the grounds are shifting their locations in the coffee bed, so there is not a definitive set of 'top' or 'bottom' grounds.

But in the case of espresso extraction, the top always extracts more than the bottom (in a cylndrical basket, anyway) because the top always gets the fresher water, which is a more effective solvent.

In the case of drip brewing, the amount a given section of grounds will extract, relative to other sections, is based on several factors (I'm going to stick to just the biggies here):

-temperature (let's call that almost-irrelevant for this discussion)
-the concentration gradient in that area (affected by how clean the water is and how much solids are in the grounds)
-how much contact time the grounds in that area have with the water.

In espresso extraction, the concentration gradient is dominant in determining the relative extraction of different areas of the coffee bed. in drip brewing, the contact time is the dominant factor.

In drip brewing the relative concentration gradients of different areas are hard to figure out due to the turbulence in the slurry. However, proper stirring at the right times can help rebalance the concentration gradient to limit extraction favoritism of one area over another (also mentioned in that book, I think. I no longer have it memorized!)

But the most important factor with Chemex or manual-drip cones, at least according to the combined efforts of my taste buds and my ExtractMOJO refractometer, is that the dwell time of the high-and-dry grounds may be as little as HALF the dwell time near the bottom of the filter. For instance, in James' video (James, I am not picking on you; I just have no other video to reference right now) the total extraction time is 3 minutes and 45 seconds but a mass of grounds starts sticking high-and-dry 2 minutes and 20 seconds before the bottom is done extracting! An area of grounds that spends half as much time extracting will extract less than an area extracting for twice as much time.

This is why it is important to not let any grounds stick up on the filter walls. Even in my Abid brewer, with a 1:00 dwell time and a mere 1:00 drawdown time, if I let a small mass of grounds stick up around the rim of the filter, I can predict the brew strength will drop by 0.1%. (roughly the same as extracting 1.4% less of the total dry grounds mass.) A biggish mass, and brew strength will drop by 0.2% or more. God forbid the entire filter wall is coated, as it is in most peoples' Chemexes, and total extraction levels drop precipitously. My Abid coffee is full, round, and balanced ONLY when no grounds stick to the sides of the filter, and all of the grounds are in the bottom dome-shaped mass.

As for many people who have enjoyed Chemexes, I will posit a new possibility: If you overdose (in other words, use much more grounds than the standard 17:1) enough and use a coarse enough grind, pour in many stages, and stir appropriately you can avoid the astringency of overextraction, and you can get a clean-tasting cup. BUT you will definitely have sacrificed sweetness and roundness, and will have wasted grounds in the process. Much like a Clover, the Chemex design is flawed, and the only way to create a non-astringent, reasonably decent coffee with standard brew strength is to overdose, underextract, sacrifice some sweetness, and waste a lot of expensive coffee.

I will now hunker down and prepare for you to shred all of my pseudo-scientific assertions.

-S. Rao, charter member of the A. Schecter Fan Club
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Re: Chemex: why you should hate it

Postby seankohmescher on Mon Feb 23, 2009 5:49 pm

Life is beautiful. Topics and discussions ABOUT COFFEE is why I love this website. There is nothing like many well renowned people having a debate about coffee. Beautiful.
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Re: Chemex: why you should love it

Postby Matthew P. Williams on Mon Feb 23, 2009 6:20 pm

David LaMont wrote:Last thought--I think we're getting hung up on the final drainage of the last drips of water through the coffee bed that resulted from our pour method. The Japanese shops I went into seemed to have a great solution for this. They MOVE THE FRIGGIN' FILTER. Just like I never saw a coffee shop operator pour a coffee in less than 3 additions of water (prewet, intial pour, final pour), I also NEVER saw a shop operator allow the water to drain completely from the filter into the customers cup. That's why all the Japanese pour-over devices come in 2 pieces--the filter and the receptacle. Hario does it. Melitta does it. Kalita does it. Chemex doesn't (gasp!!).


The Chemex filter is durable enough to remove while it is still full of liquid, though I guess this only applies to tho square ones...
Mmm, juicy. Tastes like juice. Bean juice.
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Re: Chemex: why you should hate it

Postby David LaMont on Mon Feb 23, 2009 7:13 pm

I agree. I pulled the filter early on every Chemex I brewed today. Even the non-square filters hold up really well.
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Re: Chemex: don't hate it, embrace it

Postby Andy Schecter on Mon Feb 23, 2009 7:19 pm

Scott Rao wrote: In drip brewing the relative concentration gradients of different areas are hard to figure out due to the turbulence in the slurry. However, proper stirring at the right times can help rebalance the concentration gradient to limit extraction favoritism of one area over another


Seems to me this is a key point. Several small addition of water, keeping the grounds wet as long as possible, may do a far more even job of extraction that just an initial wetting followed by a single massive pour. In fact, I heard of a guy who was even planning to sell a little device that added water gradually!

Scott Rao wrote: My Abid coffee is full, round, and balanced ONLY when no grounds stick to the sides of the filter, and all of the grounds are in the bottom dome-shaped mass.


Well perhaps the goal of better Chemex technique should be to make this happen as much as possible. It is probably similar to the benefit of the syphon dome, but because Chemex doesn't have the vac pot's advantage of an initial full immersion, it is probably far more important in Chemex brewing.

Scott, in this discussion you have the considerable benefit of having sweated out the job of tasting and measuring many many Chemex extractions. There is no substitute for running real experiments and collecting real data. Kudos to you for that. But while you've made a case for how challenging it may be to use the Chemex, it does seem like there are some techniques that are a lot better than others.

I think you got a kick out of putting such an obnoxious subject title on the original post in this thread, and you succeeded in getting a lot of people to pay attention!
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Re: Chemex: I blame my technique, not the brewer

Postby Matthew Kolehmainen on Mon Feb 23, 2009 8:29 pm

David LaMont wrote:I also NEVER saw a shop operator allow the water to drain completely from the filter into the customers cup.


Has anyone tasted the last bit of coffee to drain from the chemex filter? I did on several chemex I made today. The last bit of coffee to drain was lighter in colour than the bulk of the brew, but not by much. As well, it didn't taste overextracted. Just weak. This seems to indicate that we're not necessarily overextracting the cone in the bottom.

Looking closely as the chemex brews, I also notice that not all the water is traveling through the bottom section of the cone. Much of the coffee is being drawn through the filter paper higher up, then traveling down and dripping off the bottom of the cone. This is especially apparent if you pay attention when you rinse your filter.

Having said that, of the maybe 50 chemex I've had, 5 have been okay, with maybe 1 good. I find it's very technique dependent, and I haven't mastered that yet.

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Re: Chemex: why you should hate it

Postby Scott Rao on Mon Feb 23, 2009 9:17 pm

Andy Schecter wrote:Scott, in this discussion you have the considerable benefit of having sweated out the job of tasting and measuring many many Chemex extractions. There is no substitute for running real experiments and collecting real data.


Thank you for saying that and for not skewering me for my lack of hard evidence about concentration gradient vs. dwell time as the dominant factors in espresso and drip respectively.

Feel free to skewer me in a private email :)

(that fan club comment must have worked to protect me from the wrath of the Schectermatic B.S. Detector!!)
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Re: Chemex: why you should hate it

Postby Luke Shaffer on Tue Feb 24, 2009 7:52 am

I am in favor of brewing experimentation and questioning practices rather than doing something "because that's how it's been done for years".

Scott, I own your book and have found it to be a valuable resource for my own professional education. For much of my coffee career, however, I've had to figure things out own my own, for my tastebuds, and then explain it to my customers. For what it's worth, I very much enjoy coffee brewed on MY Chemex. I also have been known to enjoy a French Press, Syphon, and (eek) Clover. There are different methods required to get the most out of each brewing device, and arguing over personal preferences as to which is best can go on forever. To me it's like debating your favorite coffee or sports team. We are all influenced by our tastes.

Having said that, it took me quite a bit of experimentation before I was consistently satisfied with the results of my Chemex brews. I'm not taking credit for any of this as it's been assembled from things I've read here and elsewhere. It's not as easy as one would first think, and I don't propose this as the ultimate final word- but it works for me so I thought I'd share it here:

* start boiling your water... I like a really full kettle so it's easier to control the pour later (I am not cool enough to have the sweet little pouring kettle)
* grind coffee (today I used 42g for 20oz final volume, ground ~ paper flat on my baratza)
* immediately prewet the filter with boiling water
* pour the "prewet" water out of the chemex (via the pouring channel) without disturbing the filter seal against the glass. A bad seal causes water to exit out higher in the cone.
* put coffee into filter, shake until level
* after about 30s to 1min, kettle water should be cool enough to begin pouring
* "bloom pour" -pour as lightly as possible over the coffee, wetting the top surface without hitting the edges. Coffee starts to bloom, and probably takes about 30 seconds before it reaches a steady state.
* "fill pour" -pour in a light spiral pattern from inside to outside, again taking care not to hit the wall with the water (channelling). Fill to about 3/4 full.
* "refill pour" -as the water level drops, pour lightly around the edges to incorporate the coffee clinging to the filter wall, without creating a lot of agitation. I don't like seeing a super thick crust of coffee high and dry- I want it saturated. Any time I've left that crust on there I've found the resulting brew lacking body. I used to do a stir at this point, but I've gotten better at using the water to do my stirring.
* keep adding water in a light spiral pattern to keep the level somewhat constant. This keeps the temperature up (I measured it!) and the light pour prevents excess agitation and channelling
* keep an eye on the final brew. I use the 8 cupper so the belly button indicates ~ 20oz. I yank the filter still full of water and put it in my sink carefully so it finishes filtering down the drain.

Checking the filter later while enjoying my delicious coffee... there's a very thin coating of grounds the full height of the cone, but probably 90% of the coffee is settled to the bottom of the cone. Again the temp stayed pretty constant throughout, per my measurements only dropping a couple of degrees from initial fill to when I pulled the filter. I'd say the total brew time including the bloom pour was right around 4 minutes.

Just my two cents.
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Re: Chemex: why you should hate it

Postby Scott Rao on Tue Feb 24, 2009 5:35 pm

Luke,
Thank you for sharing your definitely-competent Chemex technique. I hope others are inclined to do the same, as I had hoped this discussion would center more on technique than it has (perhaps I should have started the thread more gently?)

I'd like to make two comments about your technique:

1. I have found a gentle but thorough churning of the grounds during the bloom, or preinfusion, phase is quite useful. Interestingly, I find that just pouring into the grounds without churning runs the risk of unevenly wetting the coffee. It seems the spots that get wet first attract more water, while spots that start out drier repel more water (relatively speaking). The churn helps to ensure all of the grounds start extracting at the same time. I do believe that the attract/repel effect is decreased when a coarser grind is used.

2. I have noticed that the only successful Chemex brews (by my personal standards, being somewhat allergic to even moderate astringency and bitterness) involve breaking the age-old 17:1 ratio of water to coffee (yours is approx. 13.5:1, but depends on whether you are measuring your 20oz of water when it is hot or cold). I'm not a fan of using anything under 16:1, flavor-wise. But it seems that with Chemex and Clover in particular, there is not much choice if you want decent brew strength (minimum 1.2%) and don't want the astringency and bitterness that comes with too much overextraction.

Cheers,
Scott
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Re: Chemex: why you should hate it

Postby Scott Rao on Tue Feb 24, 2009 6:12 pm

Scott Rao wrote:In espresso extraction, the concentration gradient is dominant in determining the relative extraction of different areas of the coffee bed. in drip brewing, the contact time is the dominant factor.


I'd like to edit that because it was poorly phrased.
What I should have written is that I don't worry about the contact time's effect on evenness of extraction in espresso extraction because contact time seems pretty uniform across the whole mass of grounds.

However, in the case of a Chemex with high-and-dry grounds, the possibility of some grounds spending 2 minutes extracting and other grounds spending 4 minutes extracting seems like a near-guarantee of very uneven extraction. This is not to downplay the importance of concentration gradient, but just to point out that that 2-minute differential is a serious problem that I would have no idea how to overcome.
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Re: Chemex: why you should hate it

Postby Scott Rao on Tue Feb 24, 2009 6:20 pm

Rich Westerfield wrote:It got us thinking about using an Aeropress for applying water instead of a kettle (the diameter works for our #1 filters). The Aeropress cap is a showerhead and the plunger can be controlled to a small degree to apply bursts or a steady flow. Will be interesting if there are marked taste differences between wide dispersion vs. a controlled pour. I'd like to think someone's done this before for a cone filter pourover setup, but don't recall seeing anything on it.


Rich,
I have done work on this, and would be happy to help you benefit from my mistakes and progress. It may be a little to detailed to type, so feel free to email me your phone number and I'll give you a ring if you'd like to discuss it. (I'm not reachable by phone)

Best,
Scott
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Re: Chemex: why you should hate it

Postby Andy Schecter on Tue Feb 24, 2009 6:26 pm

Luke, I think the technique you outline takes care of some of the problem areas that Scott mentioned.
1. You keep the temperature up in a good range.
2. You keep the water level up so that grounds are not left "high and dry."
3. Your pouring gives gentle agitation
4. I love the way you yank the filter while water is still covering the grounds (helps with #2 above).
5. Four minute brew time sounds great.

Good work. I'll be over Saturday morning for a Chemex pot! :)
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Re: Chemex: why you should hate it

Postby Scott Rao on Tue Feb 24, 2009 6:31 pm

Andy Schecter wrote:Good work. I'll be over Saturday morning for a Chemex pot!


I thought you only drink espresso?
What next, tea? Are you getting soft?
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Re: Chemex: why you should hate it

Postby Andy Schecter on Tue Feb 24, 2009 6:36 pm

Scott Rao wrote: I have noticed that the only successful Chemex brews (by my personal standards, being somewhat allergic to even moderate astringency and bitterness) involve breaking the age-old 17:1 ratio of water to coffee (yours is approx. 13.5:1, but depends on whether you are measuring your 20oz of water when it is hot or cold). I'm not a fan of using anything under 16:1, flavor-wise.


He's measuring the 20oz hot, since he measures it against a mark in the vessel as it brews. When I calculate out Luke's ratio with ExtractMojo, I get ~15.6:1.

Scott Rao wrote: in the case of a Chemex with high-and-dry grounds, the possibility of some grounds spending 2 minutes extracting and other grounds spending 4 minutes extracting seems like a near-guarantee of very uneven extraction. This is not to downplay the importance of concentration gradient, but just to point out that that 2-minute differential is a serious problem that I would have no idea how to overcome.


Doesn't Luke's technique solve the problem by keeping all the grounds pretty much submerged in water and then yanking the filter before they start to become uncovered?
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Re: Chemex: why you should hate it

Postby Andy Schecter on Tue Feb 24, 2009 6:40 pm

Scott Rao wrote:I thought you only drink espresso?
What next, tea? Are you getting soft?


I only drank espresso until I got ExtractMojo. Then I started to make brewed coffee.

But once I got the Speedster I pretty much forgot about brewed coffee!

If you came up with an ExtractMojo or a Speedster for tea-making, I'd undoubtedly take up tea!
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Re: Chemex: why you should hate it

Postby Scott Rao on Tue Feb 24, 2009 6:50 pm

You got a speedster? Any other secrets you've been keeping?

I have in fact been measuring tea extractions but have hit some roadblocks.

I was going to send you some tea straight off the farm from China in April, but I guess that would be a waste b/c I don't have a extract-mojo system for tea. Maybe I'll just have to send your tea to Amber.
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Re: Chemex: why you should hate it

Postby phaelon56 on Tue Feb 24, 2009 7:02 pm

I think this thread title alone is enough to rile some people up but this is one of the most spirited yet also informative discussions I've seen here in awhile - and that's a good thing.

1) I don't know Scott in any way other than by reputation (and it is a good one) but I feel obligated to point out that he was NOT the person who brought up the Raomatic (it was Andy Schecter who did and no I don't think he was taking bait). Scott replied with a paragraph or so to address the Raomatic concept and its relevance to this discussion but then went right back to the topic at hand.

2) It seems unreasonable and not especially logical to attempt direct comparisons between a puck of finely ground compressed coffee under pressure in a portafilter with more coarsely ground coffee that is immersed in a much larger volume of fluid. The fluid dynamics and thermodynamics alone make these very dissimilar despite the fact that there's ground coffee, water and extraction of solubles involved in both scenario's.

3) I've been making coffee at home - sometimes by the cup and sometimes by the pot - with various size Melitta cones since around 1977.... the year I discovered the fact that all arabica whole bean coffee ground at home and fresh brewed was a whole lot better than my parent's Maxwell House. I did own a Chemex for a brief spell but never felt as comfortable with the overall design as I did having the separate pot and filter holder that I do with Melitta.

4) My interest in coffee until perhaps ten years ago was focused solely on having the best possible cup at home and I never gave any thought to comparative differences between Melitta and Chemex but they are both open gravity based cone shaped systems so I'll veer off a bit here and offer my personal observations - limited as they are - based on Melitta process.

Don't recall where I learned to do it but for as long as I can remember (the period of 1978 to 1988 is still very fuzzy for me but I recall doing this in '77 before the lights dimmed) my process has always been:

- Using water just below the boil pour in just enough, in a circular motion, to totally wet the grounds in the filter but then back off and allow the initial bloom of steam to subside and the grounds to be saturated but with no water in the cone above them.

- Pour in a bit more water - straight down at first but then in a widening circle that moves out toward edge of cone as the level rises and bring level about 3/4 of the way up to top edge of cone.

- Allow about 1/3 of that water to pass into the vessel and then pour remaining water in - this time beginning the pour straight down the edge of cone - not in the middle. This final pour is done once again in a circular motion but starts at the top edge and moves around and downward - pushing the accumulated coffee on the sides of the cone back into the middle of the remaining fluid and continues forcing agitation.

I've actually never thought to dissect and document this process until reading this thread because it's been an automatic and subconscious process for me for so many years. My guess is that the distribution of coffee averages out as being fairly consistent due to the pre-wetting, the distribution onto sides of filter (caused by the widening circle pour stage) and the subsequent push back towards the center and further re-distribution (caused by the inward moving circle of the final pour.

It's not an ideal system by any means but I have yet to try coffee from any other system - Clover, vacpot or otherwise - that tastes markedly superior. Different yes and easier or more suited to larger batch size or commercial preparation unquestionably but better? Not for my tastes.

Yes there are numerous shortcomings including lack of truly accurate temperature control and the taste artifact of the filter paper (which my palate is not refined enough to detect - and I love the clean taste of vacpot but that's a whole different beast). I like manual cone drip coffee. Perhaps I need to get a Chemex and do a Melitta vs. Chemex smackdown.....
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Re: Chemex: why you should hate it

Postby aaronblanco on Wed Feb 25, 2009 10:02 pm

Scott Rao wrote:Luke,
Thank you for sharing your definitely-competent Chemex technique. I hope others are inclined to do the same, as I had hoped this discussion would center more on technique than it has (perhaps I should have started the thread more gently?)


Hi Scott.
I do believe people shared many a Chemex technique in a dedicated thread for that on this board. Firefox or Chrome do not show the search bar for Coffeed up top; but I believe IE does. Or you could just look it up the old-fashioned way.

[Edit: Here's the thread: http://coffeed.com/viewtopic.php?f=17&t=1776 ]
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Re: Chemex: why you should hate it

Postby James Hoffmann on Thu Feb 26, 2009 12:58 pm

I am enjoying this thread, and the only thing really annoying me is not having the time to do a bunch of experiments based on what I've read. Hope it keeps rolling - no idea what I was on about in the other thread about coarser than press grind though!?
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Re: Chemex: why you should hate it

Postby David LaMont on Sat Feb 28, 2009 8:26 pm

I've been brewing like crazy tonight, playing around with a new Vee Gee Refractometer in an effort to see the effects of different pour techniques on the Chemex output. To keep record of the results, I created a crappy little Excel sheet to aid in some of the basic math. Initially I was just tossing in numbers and then referring to a paper copy of the Strength vs. Extraction Gold Cup chart, but I realized that was stupid and have set about creating a workable chart on Excel so that I can plot my results. (I realize that I could just purchase ExtractMojo, but I don't have the $$ and I want the chart now)

Most of the chart is pretty easy to create so far--Soluble yield on the x-axis (14-26%), Soluble Concentration on the y (.4-2), but I'm hitting a roadblock with the "Brewing Ratio" lines. How are they derived? Any suggestions as to how to bribe excel into charting them for me?

Damn, I wish I had paid more attention in Stats class.
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Re: Chemex: why you should hate it

Postby Scott Rao on Sat Feb 28, 2009 8:38 pm

David,
Beware three potential obstacles:
1. Your refractometer may not accurately read coffee. The ExtractMOJO refractometer is specifically calibrated for coffee.
2. Please consider weighing your water to guarantee your ratio is what you think it is. One of the things Vince Fedele, inventor of ExtractMOJO brilliantly compensated for is the fact that near-boiling water is about 4% less dense than cold water. Weighing your water ensures your water temp doesn't matter.
3. The old charts have some small math errors in them; another thing Vince fixed along the way.

If you can afford ExtractMOJO, go for it. It's fun and will save you time and headache.

Good luck,
Scott
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Re: Chemex: why you should hate it

Postby David LaMont on Sat Feb 28, 2009 9:35 pm

Headache is right. I'm working backwards from a chart that clearly isn't very precise.

Thanks for the bits of advice. 1. I've calibrated the refractometer according to the manufacturer's instructions, my only concern is converting from Brix % to TDS %. Currently I'm multiplying the Brix reading (measures to 0.1%) by .85 to get TDS%. Does anyone know of a better conversion method? I'm curious to know how the EM refractometer is calibrated--is it simply a Brix meter fit to a better scale or is it actually measuring something different altogether? I've seen refractometers for everything from honey to milk to antifreeze. What's the defining difference in how they operate?

2. My scales are indispensable--I wouldn't attempt to brew pour-over without one.

3. Specifically, what are the errors? You have the power to alleviate some of the headache if you know.

Thanks!
David LaMont
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Re: Chemex: why you should hate it

Postby Andy Schecter on Sat Feb 28, 2009 9:49 pm

David LaMont wrote:I'm hitting a roadblock with the "Brewing Ratio" lines. How are they derived? Any suggestions as to how to bribe excel into charting them for me?


If anyone's interested, PM me your email address and I'll send you the Schectermatic (tm) Soluble Yield Calculator in Excel format.

See the screenshot below. You fill in the three numbers highlighted in yellow (light blue is optional). The sheet calculates the rest.

The normal retail price for this technology is only US$399. For a Limited Time Only, it is available for the price of one beer, payable next time we meet. :wink:

Image
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Re: Chemex: why you should hate it

Postby Andy Schecter on Sat Feb 28, 2009 10:33 pm

David LaMont wrote: 1. Currently I'm multiplying the Brix reading (measures to 0.1%) by .85 to get TDS%. Does anyone know of a better conversion method? I'm curious to know how the EM refractometer is calibrated--is it simply a Brix meter fit to a better scale or is it actually measuring something different altogether? I've seen refractometers for everything from honey to milk to antifreeze. What's the defining difference in how they operate?


0.85 is just an approximation. Values of 0.82 - 0.85 are commonly used.

All of the handheld refractometers work the same way. They don't measure brix or coffee TDS directly, they can only measure refractive index. Then they internally convert it to brix, percent battery acid, percent antifreeze, etc, according to a complex predetermined formula or table.

Vince Fedele and others at GHCC have spent a LOT of time collecting data on how to best make the conversion from RI to coffee solids. Their refractometers therefore display TDS readings that are more reliable than what we get with a Brix refractometer and a multiplying factor.

David LaMont wrote: 2. My scales are indispensable--I wouldn't attempt to brew pour-over without one.


Amen to that! For the benefit of other people, I would simply add that if you want to make accurate % TDS measurements, always use weight readings. OTOH, if you like making mistakes, confusing yourself, and misleading others, by all means use the usual idiotic mix of weight and volumetric measurements.

David LaMont wrote: 3. Specifically, what are the errors? You have the power to alleviate some of the headache if you know.


As I understand it, past errors include:
a. failing to compensate for the change in density of water as it goes from room temperature to brew temperature
b. converting TDS improperly: eg, 1.3% = 13,000ppm, not the 1,300 that the SCAA has been teaching
c. subtracting the brew water's TDS reading (eg, 150ppm) from the improperly converted coffee TDS reading. For example, the proper calculation: 13,000ppm - 150ppm = 12,850ppm. The SCAA (improper) calculation 1,300ppm - 150ppm = 1150ppm.

David, THE MOST IMPORTANT THINGS you can do to get reasonable accuracy are: COOL YOUR COFFEE SAMPLE DOWN TO ROOM TEMPERATURE before placing it on your refractometer, and WAIT AT LEAST 30 SECONDS to allow the liquid and the glass to equalize in temperature before taking a reading. If you don't do these things, your readings will be worthless.

Also, paper-filtered coffee (eg, Chemex) gives the most reliable refractometer readings. Metal-filtered coffee (french-press, espresso, etc) are trickier.
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