This post should probably start with a disclaimer – I did not pay for my ExtractMojo, it was very kindly sent to me by Vince Fedele at Terroir Coffee to use and give feedback upon.  I am very grateful to both him and Andy Schecter and Scott Rao also for getting me involved.

In many ways I am surprised that this isn’t a hotter topic of conversation, especially online.  Then again many of you reading this may have done the same thing as me – download the trial software, have a little play, think it is a cool little automated coffee brewing control chart.  I sorely underestimated it.

Given a second chance I’ve gotten stuck into assessing the way I am brewing coffee.  It has proven extremely enlightening.  I have come to a rather worrying conclusion:

Great coffees are letting us get lazy.

I should probably explain that a little bit more.  In coffee brewing there are very few fixed, set in stone, rules.  The closest we have is that when you evenly extract between 18-22% of the ground coffee during the brew then you end up with a good tasting brew.  Properly brewing within those boundaries tastes better than outside of them.

Most of us are guided by our tastebuds when we brew coffee.  I suspect we’ve been tricked a little by stellar coffees.  For example I was very fond of a coffee last year from Kenya that was a peaberry lot from Muchoki.  It was very tasty, very distinct, very characterful and interesting.  So much so that even a bad brew, an underextracted brew, tasted pretty good.  There were tonnes of fruit notes, a pleasing sweetness, it was clean and crisp.  Yummy!

However, in hindsight, I’ve come to see that I was enjoying an underextracted, but updosed brew that hit the strength marker and was sufficiently interesting and tasty not to make me work harder.

This is where a tool like the ExtractMojo comes in.  Over the last couple of months it has pushed me, challenged me and looked at my coffee brewing with cold emotionless eyes.  Nothing else has pushed me so hard to try and improve what I do, and how I brew coffee.  Recently the coffee I make has been tasting even better, and this makes me very happy – though I suppose  a bit embarrassed too.  I should add (here if nowhere else) that I am not saying that increases in greens quality have caused a decrease in brew quality.  I have no evidence of that.

It took me a little while to get my head around the software.  I’d come to it used to brewing control charts, but also used to controlling more variables than it let me.  1  After a little while it made more sense, and what really surprised me was that once you understand the relationships then you realise that the software doesn’t just analyse the brew, it also offers a route to fix bad brews which was eye opening.

People will always dismiss tools like this as missing the point, that taste is always more important than numbers.  Taste does of course win.  Yes, you can create a brew that falls within the 18-22% range that is poorly/unevenly extracted and tastes bad.  This is missing the point.

Tools like this are an incentive and a route to better coffee brewing.

Your coffee may well taste great.  In fact it probably does taste great, as the raw materials are exceptional.  That doesn’t mean that it couldn’t taste better.  Being satisfied is a terrible place to be.

  1. By now some of you are probably bored of my ramblings about TDS, brewing charts and such.  I will continue to be a big fan of programs like the SCAE Gold Cup program for spreading awareness of brewing ratios, extractions and paying attention to the mechanics of extraction.  ↩︎

51 thoughts on “ExtractMojo

  1. I have been thinking something very similar for the past week, although for me it was discovered following more regular use of my bottomless portafilter (which was returned after a very long loan last week). I discovered I have become a little sloppy during busy periods at the market but based on very positive feed back from customers had failed to pick it up through the great coffee. A good look at the portafilter has helped me to correct that inaccuracy, its taught me a lot about using every thing at my disposal whilst I brew. It seems that lots of pieces of “technology” come in and out of fashion having been talked about online and as the chatter dies down bits and pieces get left in draws gathering dust, just because people aren’t talking about something doesn’t mean you can stop using it!

  2. James – this is brilliant.

    For the past year I’ve been playing around with my TDS meter (from SCAA) and a portable glass refractometer and reading Ted Lingle’s Coffee Brewing Handbook. I assume you’ve read this & possibly used these other measuring tools?

    What I’m wondering is, if you have used the other tools & followed the reference’s in Lingle’s book are you experiencing different/better results with the new software & the ExtractMojo?

    Also, have you used their new Espresso Refractometer and how effective have you found it? I’ve experienced less success obtaining useful measured results with espresso (at least with the tools I’m using here).


  3. So…continuing our twitter discussion…

    I wish I understood the pricing structure that Terroir has established. I understand that they’re not in the technology manufacturing business, and as such the prices they need to charge are higher in order to cover their expenses. But for $399-$899? This is great for a business (which maybe they’re marketing to) that wants to improve quality and consistency, but not the individual who wants to learn and investigate on their own. I’ve been thinking about this for a while, ever since Andy dropped by with his, so maybe I’ve just been thinking about it for way too long. But I really wish it was cheaper. That said, I do absolutely see and appreciate it’s value in the workplace.

  4. Playing with different brewing tools over the past few weeks, I’ve been thinking a LOT about the ExtractMojo. I’m gonna get one as soon as I can afford it!

  5. James –

    can you explain a bit more about what this Extract Mojo has done for you and how you’ve gone about tightening up your brewing game because of it?

    I’d like to know more about the actual use of the process and how it can translate into adjusting the daily brewing that any coffeehouse would subject it to. Or is this more of a lab tool to discuss hypothetical/theoretical aspects of brewing instead of adjusting the actual daily brew?

  6. WhEhat can you achieve with it that you can’t with a good or even cheap TDS?
    More accurate? How accurate do you need?
    More convenient? Ok, but if it takes convenience to get this work done, maybe we are lazy…

  7. Hello.
    Just wondering if you are finding different results from different brewing methods. Will a french press with same measurments, grind and brewing times as filter give different read outs? I am assuming so, and if so, does the software take into account which method you are using in order to calculate results?

    Or is this only for filter brewing. I am suspecting the old brew charts to be too filter focused.

  8. @Mike – Oo! You were comment 5000!

    I think the cost is related to the fact that their meter is a proprietary technology. They’ve developed a small portable meter that has proven to be extremely accurate when measuring coffee extractions. It might be a little bit much for an individual but then what I would spend on water filtration at work vs at home is similarly disproportionate!

    I’d keep bugging Andy to borrow his!

  9. I am not sure I understand your question. The meter will analyse your finished brew, and when you give the software the data it requires (mass of water, of coffee) it will tell you how much of the coffee you extracted.

    Whatever brewing method you are using you pretty much want the same level of extraction – though the level of strength in the cup will vary depending on that method – I’d expect the way you guys use the aeropress to yield a strong cup, but that cup will test best in the 19-20% range.

    I used mine with the aeropress to try and dial in a grind or steep time quicker, and I use it with most brewing methods to double check my desired settings too.

  10. This should probably (will probably) end up as a whole new post.

    I just got a new grinder – the Uber grinder (more on that soon too). The burr settings meant nothing to me really. If I want to dial in a press grind really accurately then I would do three presses with as identical measurements (dose, brew temp, steep, technique, water weight) and varying grind. I would of course taste all three, but also meter them out. It could be that one tastes best, but still misses the theoretical sweet spot. This would push me to experiment again with three more grind settings, and then also test my repeatability. Taste still takes priority but it is nice to have something that doesn’t get palate fatigue, isn’t overly enamoured with one particular flavour and will keep me pushing towards a better cup.

    Equally – if you want to understand your technique better it is useful. Want to know the effect of each stir of a press or vacpot – you can chart it out and know.

  11. James,

    Great to see such discussions about charting brews and measuring them as a scientific balance against taste. As you know I have been suspicious of a trend towards updosed under-extracted brews.
    I have just received my Extrct Mojo (not free!) and will be charting scientific extractions against changes in temp, grind etc. This is as we do in the SCAE Gold Cup Brewmaster course, where a bugbear has always been the accuracy of the TDS metres.
    The Extract Mojo needs to deliver on its promises – accurate and fast – which it purports to do.
    Let us see.

  12. In your tests, are particular methods coming in way off the mark using ‘standard’ brew methods? Is there a trend that you’ve seen with the brew methods before testing? Updosed underextraction being the most common?

  13. Hi guys,

    just curious as I’m not so keen on spending several hundred bucks on the Mojo, is it possible to do TDS measurements with an ordinary TDS meter? or does it have to be something Uber like the Mojo to give you accurate numbers?

    Oh and what’s this Uber grinder you mentioned?


  14. James,

    First, before critiquing something you said, let me say thanks for bringing some badly-needed attention to ExtractMojo. Until they try it, no one will know what they’re missing. Hopefully your stamp of approval will motivate more people to try it.

    As you know, I disagree with the point that “great coffees are getting us lazy”. If this was true, then please explain how you might have extracted differently, had you been in the business 20 years ago and didn’t have access to the same quality green. Given that you have noted the recent tendency to “updose” and under-extract great coffees, one would have expected the opposite to have happened as better, more expensive green became available: people would want to conserve, not waste, expensive coffee.

    I would propose that the reason for the recent, frequent underextraction of large doses in cafes is due to something else: the increased focus on the methods that challenge baristas’ ability to extract relatively evenly from all areas of the coffee bed (clover, chemex, espresso (*I’m referring only to doubles and triples made in cylindrical baskets) and the decreased focus on the methods that more easily achieve a relatively even extraction (auto drip, french press, tapered-single-basket espresso).

    After all, few, if any cafes are updosing/underextracting their french presses and fetcos the way people seem to routinely updose/underextract their chemex/clover/espresso. If the trend toward underextaction were due to better coffee quality, one would expect a similar frequency and degree of underextraction for all brewing methods.

    As an example using variations on one brewing method, I see much higher grounds: water ratios being used, on average, for one-cup pourovers than for larger-batch auto drips. Every one of those cafes underextracting one-cup pourovers were brewing them in a way that guaranteed a very uneven extraction, while one would have to try pretty hard to make an auto drip machine produce such an uneven extraction.


  15. Hi Jake,

    thanks for the suggestions, I did some searching and stumbled upon the same thread so I know a bit more now.

    I’ve found a bunch of refractometers on ebay, 20 odd quid for one but there are so many types I don’t know what to choose. Most of them are to measure the salt amounts in water, but I also found some dedicated for measuring sugar levels in juices and stuff like that. Should I aim for anything particular? range of 0-25% or more?

    Would appreciate any tips:)


  16. Hey Tom,
    I just got off the phone talking to Vince, at Terroir, one of the creators of the ExtractMojo. What I found out is that the R2Mini (listed on the Reichert page) and analog meters lack the resolution required for coffee. The R2Mini that I linked to earlier (http://www.reichertai.com/products.html?productID=37), is calibrated for brix, the amount of sugars in water. The scale is 0.0 to 62.0% Brix, way too wide of a range and not precise enough for coffee. The ExtractMojo is calibrated for coffee, which is in a much narrower range and needs much more precision. Similarly, if you got one of those analog ones, because of the range, the readout would effectively be no change, because it’s such a small change compared to that of water.

    Furthermore, the conversion that was used on coffeegeek (brix measurement X .85) isn’t calibrated to any temperature. As the coffee cools, the refractive index changes. So basically, if using the brix formula on the CG site, you end up with a imprecise number to start with (because of lack of precision on a brix spectrometer for coffee) and then use a conversion that is off due to temperature variations, you end up with a completely imprecise measurement.

    In this case, I humbly cross-reference another one of James’ posts: http://www.jimseven.com/2009/05/19/the-importance-of-being-wrong/

    The ExtractMojo differs from anything on the market due to its precision and calibration, which both the R2Mini calibrated for Brix lacks and the old school analog style ones. Hopefully Vince will be able to post some more information, as he has many years of experience and a deep level of understanding of the underlying theories going on.

  17. Great to see all of the interest and activities here on James’ blog.

    A refractometer is designed to read refractive index and temperature. Some more expensive refractometers have peltier effect temperature controlled sample trays to maintain samples to w/in 0.001 Deg C and can resolve nD to six decimal places. We used such a Refractometer, as well as a LabWave 9000 as lab standards to correlate the custom r2mini Coffee Refractometer sold by GHCC. Refractometers can be correlated to read % Concentration of many liquid solutions, where refractive index is directly related to density and temperature, and thus concentration. There are specialized refractometers scaled for reading salinity, sugar concentration of fruits (for determining prime harvest time), oils, fats, syrups, soy, honey moisture, sodium chloride, alcohols, and many others. Each application requires a separate correlation and temperature compensation (in order to be accurate for that application) for the ranges of concentration and temperature used.

    The Reichert r2mini Coffee Refractometers sold by George Howell Coffee Co are specifically correlated to directly read % Total Dissolved Solids of coffee to 0.01 % , and is specifically temperature compensated for coffee.

    In contrast, the standard, off the shelf r2mini refractometer available directly from Reichert, is correlated instead to directly read % TDS of Sucrose in solution (where Sucrose is the only dissolved solid), a scale called BRIX, or Degrees Brix or % Brix. The BRIX scale is also temperature compensated for Sucrose in solution. Neither the density nor temperature compensation curves for Sucrose are the same as for Coffee.

    This is why the previous estimates provided of Brix x 0.85 ~= % TDS for Coffee are not accurate, and will not work over a 15-20 Deg C temperature range. A significant degree of precision is required for an accurate reading and for use with a Coffee Brewing Control Chart.

    Regarding refractometer costs, because the BRIX scale applies very broadly to a wide range of food/beverage processing industries, volumes are higher, and instrument costs are lower. Specialized applications, as well as the additional resolution required for accuracy at the lower concentrations (0-5.00% vs 0-62.0%) for coffee refractometer all contribute to the laws of supply and demand, and effective prices.

    A final note on costs. There is a now $99 version of ExtractMoJo software, for Coffee only (less Bypass, Iced and Espresso modes) here:

    or for $399 bundled with the Coffee Refractometer here:

    Other MoJo products are here:

    Regards to the entire group, feel free to eMail any questions.

    Vince Fedele
    Chief Technology Officer and COO
    George Howell Coffee Co

  18. > can you explain a bit more about what this Extract Mojo has done for you
    > and how you’ve gone about tightening up your brewing game because of it?
    > I’d like to know more about the actual use of the process and how it can
    > translate into adjusting the daily brewing that any coffeehouse would subject it to

    ExtractMojo allows you to play with the everyday variables that we all play with, but with unprecedented ease and precision.
    For instance: If you grind a little finer, you can steep for a little less time. Extractmojo will help you quickly zero in on exactly HOW much less time. Then you can evaluate whether too much sediment or astringency comes along with the finer grind.
    Another example: how strong do you want your featured coffees to be? 1.3% total dissolved solids? 1.4%? 1.5%? The instrument and software will guide you towards making accurate comparisons, while ensuring that your EXTRACTION YIELD (which controls flavor balance) remains constant. Not so easy to do without the instrumentation, particularly since each origin will be a little different.
    Third example: those mysterious stirring techniques. Some say their siphon coffee tastes best only when stirred once clockwise then twice counterclockwise with a six inch section of the thigh bone of an ass. You might ask, how come that works best? Well, part of the answer is that stirring increases the extraction yield. Try playing with different stirring techniques, keeping everything else the same, and use the instrument to see if and how the extraction yield changes. It’s still a mysterious process, but a lot LESS mysterious with the coffee refractometer backing your taste buds.
    One more: everyday quality control at your shop. Taking instrument readings is an objective way to get an idea if your brew parameters drift away from your target as the coffee ages and your staff changes. Again, the instrument is only a backup to your cafe manager’s tastebuds, but backup is GOOD.
    Summary: Used with care, ExtractMojo and the Coffee Refractometer help strip away some of the hocus-pocus involved in brewing consistently excellent coffee.

  19. I think your summary is pretty much spot on for me. I’ve used it to dial in grind settings quite a lot – and on a side note I wonder if this is as close as we will ever get to being able to communicate grind size? (i.e. use the grind that with a 60g dose, 990g of water and 4 minute steep that yields a 19% extraction – though that obviously doesn’t really communicate particle size distribution.)

    I’ve used it to make more calculated adjustments to grind or steep time, to help reduce trial and error.

    One thing I hadn’t tried was playing with cup strength targets, keeping yield constant. It makes me wonder how scalable grind size is with infusion methods – in theory it should be the same grind for a press, regardless of strength goal but I doubt that will turn out to be the case!

  20. After reading your blog posting & talking with Vince @ Terroir for a couple hours today I ordered up the ExtractMojo Coffee & Espresso bundle. Can’t wait for this baby to show up !!

    Thanks for the insight James

  21. James, Have you ever considered using design of experiment techniques to dial into the optimum set of variables with as little effort as possible? You might find it a very efficient approach to save wasted time, effort and expense to dial in the ‘best’. thanks for a great blog by the way.


  22. Hi James et. al.,

    I picked up a cheap analogue refractometer about half a year ago and one thing that I’ve always wanted to do is to construct a whole series of graphs of extraction (ie. percentage extracted from the bean) vs grind size (as measured by the numbers on a given grinder) for a series of different grind sizes, keeping all other parameters constant. The idea would be to try to quantify the magnitude of difference that a particular grind adjustment makes to help you dial in any coffee – who knows; perhaps you could get it so down pat that you could always nail the second extraction of any coffee. It would also be interesting to use these graphs to investigate the effect of age and roast level. Unfortunately, I haven’t gotten very far in doing this, but now that refractometers are the new black, perhaps there’s someone out there with the time to do it? Perhaps someone with a roastery full of yummy coffee of different types? James?



  23. Hey Luca,

    I have thought a bit about this, though it will obviously vary quite a lot from grinder to grinder. I would guess that with the way the peak’s move in the grind size distribution charts you wouldn’t have a very linear line to move along – but that is just guess work.

    It would also likely apply to only one grinder model (due to size of adjustment divisions) and a particular burrset – though I shudder to think what impact burr age could have on things too!

    Off the top of my head I can think of half a dozen really useful experiments that I don’t have the time to do but would be incredibly useful. I wish the coffeed study group had worked and had been up for group experiments with kit like the Extract Mojo!

  24. I apologise for not responding to this sooner – it is a discussion that got sidetracked by conversation about the Mojo itself.

    Re: Great coffee making us lazy

    In the UK at least for a long time just about all filter coffee was overextracted. This was due to the ever decreasing gram weight in portion packs of ground coffee that most suppliers were offering – the ‘4 pint pouch’. This created most people’s very low expectations for value/quality in brewed coffee.

    I am sure it is similar in the US, the stewed pot of coffee for the free refills is likely very overextracted and bitter to begin with.

    Higher doses are, as you say, linked to technique but also (I think) to trying to stand out from regular every day coffee. By being generous with the grounds, instead of skimping to cut costs. Perhaps this is linked to the disdain that we have for auto drip brewers – though obviously by the cup brewing is more desirable than bulk brewing when it comes to customer experience.

    If the coffee had tasted bad as a result of the higher doses then we would likely have stopped doing it. The fact that it tastes ok is due to good greens with characteristics that show through and are interesting even when underextracted.

    If we know that a certain range tastes better, and I think we have known that for some time now, we have to ask why we lack the motivation to constantly hit that target when we make coffee. My suggested explanation is the quality of greens. Your explanation does make sense and fits in quite well with the constant fetishization of brewers – syphons are fashionable now, perhaps Abid’s will be next year.

  25. Thank you for all the links. This post was really very informative along with all the comments on the ExtractMojo. Wonderful brewer! Will have to order one as soon as I get back home.

  26. So I have a question…

    You talk about taste vs. “science,” but where did we get 18-22%? Taste?

    It seems like we’re trying to just be a little bit more specific about subjective things, but is there anything particularly solid about the “golden ratio” cup of coffee? Surely it wouldn’t be just bitter elements to sweet elements in the bean; that is just taste again.

  27. We did arrive at 18-22% based on taste. My issue is that people have become openly reliant on taste and haven’t used tools like this that have allowed a more objective look at the brewing process. People dismiss measurement, claiming taste is more important. Taste is more important but it isn’t either or. Taste combined with testing and measurement will allow clearer understanding of process and a path to improvement.

  28. That makes perfect sense. Here is where I get a little confused, though:

    18-22% is ideal. But say there is a coffee that tastes good at 23%, or 17%. What does that mean?

    To what extent is measuring useful? Only to completely and consistently dial in a sweet spot? Is improvement simply knowing that extracting coffee at 93º instead of 94º makes is taste better?

    So obviously the ExtractMojo is a tool for consistency. My worry is that consistency might be shooting ourselves in the foot. Recently I’ve had some coffees that meet my preference when they are underextracted (but not overdosed). El Salvadorians and Ethopians sometimes appeal to me that way. I suppose my worry is that the “science” of it will get in the way. People will refuse certain cups of coffee because they don’t fit in the parameters.

    Have you had any experience with a coffee that tastes good outside of the norm of brewing?

  29. I think we are a long way away from people rejecting cups of a scientific level.

    I think cups brewed outside of the classic range can have positive qualities – certainly very distinct coffees carry themselves well when brewed outside of the range BUT I find the cups lack complexity, often dry up as they cool and can be improved upon.

  30. Hi guys,

    how much of that ‘cup brewed at 18-22% tastes the best’ is true and how much is the power of suggestion?

    Perhaps sometimes you want to feel like that ‘proper’ cup is better.


  31. The fact that this region has been preached for 40 years now, has held up to repeated blind testing etc, means that we can be pretty confident in its useful accuracy.

    I often taste the coffee before measuring it, as going the other way around could well taint my experience.

  32. –Daniel F.–
    “But say there is a coffee that tastes good at 23%, or 17%. What does that mean? To what extent is measuring useful?”

    Hi Daniel, you ask some good questions. Accept my apologies to the group in advance for the rather long answer. I will break it up to two posts, each relevant to different points of the discussion. I agree w/James on this one. There are a few very good reasons to measure, I’ll try to explain why here, and try to answer your questions. Hats off to James and everyone in the group for an engaging discussion.

    Why Measure, Part 1
    The Midwest Research Institute developed the general range of 18-22% Ext Yield and 1.15-1.35 concentration, sometime in the 1950s and republished it in CBC Publication No. 27, 1969, p12. I have the original research and charts, eMail me if you are interested in more details. This research updated the original range from the Brewing Committee of the National Coffee Association and was adopted by the CBC, and later by the SCAA. The SCAE also uses the same Ext Yield as the accepted range, but with a higher range of concentration. The Nordic Coffee Center also uses the same Ext Yield as the accepted range, but at an even higher range of concentration. All three official associations use the same 18-22% extraction yield range today. We use 18-20% at GHCC, with a 19% default target, because we have the means to measure and set it easily using eMoJo, and feel this provides a sweeter result for most or all of our lighter-roasted coffees.

    A very important reason for measuring extraction yield is to set your brewing parameters given there might be many coffees, methods, batch sizes, grades of grind, in use. Every time you brew using a different coffee, batch size or method, it’s possible to end up with a different result, and something other than an optimum brew. We tried using the existing paper charts and conductivity TDS meters, but we found problems with the charts and conductivity meters didn’t work for coffee. eMoJo is a set of new tools we developed to modernize the method(s) and TDS instrument(s), to help identify how to hit the sweet spot with all of our coffees all of the time. It applies equally to home and or professional applications and for all methods and batch sizes.

    Unless one MEASUREs all three elements, Concentration (% TDS), Water (Weight) and Coffee (Weight), we will have no idea of where we actually are in terms of extraction yield. This applies to all batches of all coffees. For example, consider your clients who brew your coffees in their cafes. If your model is similar to ours, you provide, calibrate, and maintain their equipment and water treatment systems. Like any roaster, we want our coffees served at peak possible expression, as do our clients. Some of our café clients brew 3-4 different drip coffees, each in 1-3 batch sizes, including ICED. In a single location we can have 9+ combinations of batches. We calibrate all water doses, coffee doses, and program brewing parameters, including pre-infusion, pre-wet delays, pulse brew times, etc separately for each batch. Some clients frequently rotate specialty S.O. coffees every few weeks, those need more frequent attention.

    In answer to your question, we then measure, and adjust as necessary, usually the grade of grind is our primary variable-as we have programmed preferences known for all mfgr and models of brewers and for all batch sizes. This ensures all of our coffees are served correctly brewed in each batch size and for each method.

    I agree with you Daniel, in that you will find that if you’re very far outside of the 18-22% range, you will know something is wrong by taste, i.e, if the brew is significantly over- or under-extracted. Most of us, even if not expert cuppers, know what a great cup tastes like, and we can easily identify the defect as one or the other (when outside of these ranges). Until one measures this defect, however, one can’t know how far under-developed in terms of extraction yield, nor at what concentration level you have actually landed at.

    Taking a simple measurement using eMoJo will tell you immediately where you are, so that using your experiences, you can then navigate in the direction you want to go on the brewing control chart. I can guarantee that if you have had a great coffee you think is good at 17% yield, and you are given the chance to blind cup that coffee at 16-17 vs 19-20 vs 22-23% yield, you will pick out the 19-20% yield every time as the preferred brew. I have seen it a hundred times in the past 18-months using eMoJo in the field with our clients.

    The improvement in consistency and sweetness of all of our coffees has been nothing short of spectacular. We have had feedback from dozens of roasters who are using ExtractMoJo all over the planet who have had similar results with their clients.

    See Part 2:


    Vince Fedele
    COO & Chief Technology Officer
    George Howell Coffee Co

  33. Why Measure, Part 2

    It talks only a small error in brew water weight, and or coffee dose to knock the brewed result out of the optimum balance region on the brewing control chart. These changes happen due to equipment programming errors, lack of proper calibration of brew doses, defective fill probe sensors, dull grinder burrs, incorrect water treatment, you name it we’ve seen it. Even a new set of burrs in a portion grinder will start to drop dose weights on timed batches until they stabilize after several hundred pounds.

    We set up a client in Boston to brew a 2-liter batch of custom blended SO coffees. He measured out 125 grams of whole beans each morning, and stacked them in closed plastic containers for each days use. (He did this to eliminate portion-grinder weight errors.) Before each brew, the 125g dose was run through a commercial grinder, and into the basket it went.

    We left him at 19% Extraction Yield and 1.40% TDS. The coffee was outstanding, a combination of a Guatemala peaberry and two Kenyas he had developed with George. A few weeks later, the chef called to complain about the coffee. He was polite but quite insistent it was slightly bitter. We went out and tasted the coffee. He was right, it was slightly bitter. We measured the % TDS at….1.41%, just where we left it. However, that number is meaningless w/o the dose weights. Checking the coffee weighed in at exactly125 grams in every container he had set up for the day. However, the water weighed 2214grams, the equivalent of 2.30 liters at 94 DegC. Plotting that data in MoJo showed an extraction yield of 22.4%……just over the edge where the defect “bitter” is plotted on the chart.

    After several false leads in determining root cause of the water dose, we found that we had made an error in the type of water filter installed at the location (a lime-scale inhibiting filter –one digit different on the part number, usually reserved for Cambridge city water, which has a significant CaCO3 scaling problem in summer months). Boston’s water is soft at only 1 grain per gallon (17ppm) hard minerals, so the fill probe was unable to detect when the boiler was full, until over-filled by a full 1-inch. This caused the brewer to dose 2.3 versus the 2.0 liters programmed value, as the excess water was being vented into the brew basket during brew. We corrected the filter, and the problem was resolved.

    So, as you can see a small 15% error in the brew formula was all that was needed to knock the brew formula out of the region of optimum balance. In actual practice, if the brewer is dosing 5% too much water AND the grinder doses 5% too little coffee, you have a cumulative 10% error in the brew formula. These can be typical of many commercial brewers and grinders that use “timed” dosing versus actual weighed dosing…..

    So, in addition to answering your question “why measure” the point is that if you target the batch for your clients to be in the CENTER of the optimum region of interest, then small changes in dose due to normal variances in the equipment dosing will ensure you’re ALWAYS within the optimum region of interest, even though you might move around a bit from batch to batch. Therefore, we would never intentionally set something at 18 or 22, let alone 17%, because these portions do move around. Smaller single-serve brews require even more attention to dose weights.

    –Daniel F.–
    “Have you had any experience with a coffee that tastes good outside of the norm of brewing??

    Yes, some coffees, such as certain Ethiopian coffees are actually very low in certain acidic components normally found in higher concentrations in most coffees, and even when over-extracted develop more body w/out the bitter components normally associated with over-extraction, but these are generally rare. I have noticed a similar attribute with some Guatemala peaberry coffees. However, that said, I have never found any coffee that tastes acceptable when under-developed. The most common error is that users will updose, and simply navigate UP the brewing control chart creating a stronger under-developed coffee, rather than up and to the right along the brew formula line, w/o changing dose to fully extract, i.e., brewing longer.

    I encourage you to TRY IT, using an instrument that works so that you can experience first-hand the enormous improvement in flavor when extraction yield is adjusted to a range closer to the sweet spot.

    Concentration then becomes much more obvious as a preference for strength. One can have a very sweet coffee that is weaker, or one that is stronger. However, updosing and under-extracting is not only a waste of expensive coffee, but produces an unacceptable, or at least sub-optimum result. It is certainly analogous to using too little a dose, and over-extracting in order to get the concentration desired, at the expense of harsh bitter brews, driving the need for sugars and condiments……same problem, other side of the river……(sweet-spot range on the brewing control chart).

    Centering the extraction yield when properly applied to virtually all methods will improve the flavor, enjoyment of nearly all of your coffees.


    Vince Fedele
    COO & Chief Technology Officer
    George Howell Coffee Co

  34. “The ExtractMojo differs from anything on the market due to its precision and calibration, which both the R2Mini calibrated for Brix lacks and the old school analog style ones.”
    I’m not sure I understand this. From what I gather, the R2Mini is a digital refractometer with a given precision. If the refractory index is measured – regardless the brand of the refractometer – with a certain precision, why couldn’t all the necessary calibration for coffee/espresso be done by the software? And is it really necessary to have two different R2Minis, one for espresso and the other one for brewed coffee?

  35. Hi Walter – here is Vince’s answer to your questions:

    The question is somewhat of a non sequitur ….. “why couldn’t all the necessary calibration for coffee/espresso be done by the software?”

    It’s not the calibration that is performed by the software, it’s the correlation to scale that is done by the software. Which software are you referring to, the software embedded in the instrument or the application software ExtractMoJo? If you’re referring to the latter, inputting refractive index is meaningless to most people, it’s not a number they will remember or recall to relate to, relative to the % TDS scale we are interested in. As in other applications for instrumentation measuring refractive index, we chose to design the instrument to display the information relevant to the user, that is % TDS – directly.

    The instrument specifications for resolution and accuracy differs from the “standard” r2mini used for brix, in that and has both a higher degree of precision as well as resolution. In order to achieve this level of accuracy, the scale is limited to the refractive index range necessary for coffee TDS from 0-5%, in order to make use of the entire linear sensor array to achieve the precision necessary for measuring TDS to 0.01% resolution.

    Espresso is roughly an order of magnitude (10x) higher in concentration than that of Coffee, and requires only 0.1% TDS resolution, and measures from ~2-25% TDS. This precludes having both scales in the same instrument at this time given the technology presently available for this price range. If money were no object, of course we can and do provide an instrument that has both scales in the same instrument, that is available as a special order, cost is about $1400 (or more than two separate refractometers). This instrument was demonstrated at the SCAA show in Atlanta as well as one costing approx $14,000 that also is capable if displaying multiple coffee/espresso scales and is also available directly from GHCC. Neither of these are presently listed on our web site. We felt that most users needing to make such measurements in the field would prefer the separate, lower cost hand-held instruments.


  36. Hi James,

    thanks for publishing Vince’s reply, I see clearer now…

    Ages ago we used only one type of refractometer on university, IIRC it was some sort of Abbe refractometer, which surely must have cost a small fortune, back then. But back then computers cost a small fortune too…

    What I meant with my question was indeed, that I would be quite content if the refractometer displayed only a refractory index – at a given temperature – as precisely as possible and then the software (ExtractMojo) would provide me with the corresponding TDS value. But of course I had the price range of the r2mini in mind…

  37. […] เมื่ออาทิตย์ สองอาทิตย์ที่ผ่านมา เพื่อนผู้รักกาแฟของผมคนหนึ่ง โทรศัพท์ทางไกลมาจากเยอรมันนี เล่าให้ผมยังเรื่องเครื่อง Extract MOJO  ว่าสามารถวัดค่าการกลั่นเอสเพรสโซ่ หรือ การกลั่นชงกาแฟดูได้ว่า กาแฟที่กลั่นชงออกมานั้นได้ค่าที่เหมาะควรหรือไม่ ? ตอนที่ได้ฟังตอนนั้น ผมเห็นแย้ง และยังเชื่อว่า ไม่น่าจะพิสูจน์ได้กับรสชาติจากการชง แต่เพื่อนผมคนนี้ ผู้มีอาชีพเป็นศัลยแพทย์ด้านสมอง ยังออกลูกยุ แกมบิวท์ ให้ผมทดลองสั่งมาเล่นดู  จากการที่ได้ดูคร่าว ๆ และยังไม่มีเวลาศึกษาจริง ๆ จัง ๆ  เครื่องก็เดินทางมาถึงมือผมจนได้  และไหน ๆ ก็สั่งแล้ว ผมจึงได้สั่งทั้งเครื่องวัดค่าการกลั่นเอสเพรสโซ่ และ เครื่องวัดค่ากาแฟกลั่นสำหรับกาแฟแบบหยดชงมาด้วยเลย  เนื่องจากโปรแกรมต้องใช้ผ่าน ระบบปฏิบัติการของ Windows ซึ่งเครื่องที่ผมใช้อยู่เป็น Mac os จึงทำให้ยังไม่ได้ลง Software ตัวนี้ซะที หลักคร่าว ๆ ของการทำงานของเครื่องคือ ให้เราหยดกาแฟตัวอย่างไปที่เครื่อง จากนั้นเครื่องก็จะทำการวัดค่าต่าง ๆ ในน้ำกาแฟ แปลออกมาเป็นตัวเลขให้ไปใส่ใน Software เมื่อ Software  ประมวลผลแล้วจะแสดงค่าออกมาเป็น กราฟ อย่างในตัวอย่าง ให้ได้รู้ว่า กาแฟที่เราชง ๆ อยู่นั้นมีการสกัดตัวที่สมบูรณ์ พอดีกันระหว่าง ปริมาณกาแฟและความละเอียดของการบด และ ปริมาณน้ำที่ใช้ในการสกัดชง รวมถึง ความเห็นในการไหล เพราะหลาย ๆ ครั้งรสชาติกาแฟตัวที่เราใช้ ๆ อยู่นั้นตอนชิมอาจจะรู้สึกว่าพอดีแล้ว แต่ความจริงอาจจะผ่านการสกัดชง ที่เร็วไป หรือ UnderExtraction ดั่งเช่นที่ James Hoffman แชมป์โลกนักชงกาแฟ ได้เล่าไว้แล้วใน Blog ของเขาก็เป็นได้ […]

  38. A couple of things I’ve never understood is weather or not a refractometer is more accurate in measuring dissolve solids than a TDS meter? What did George Howell’s company see in the refractometer to consider it worth investing in when people were already using a TDS meter?

  39. We have been using the ExtractMojo software and both the filter coffee and espresso refractometers for several months in our R&D labs. We have found that the refractometers provide significantly more consistently accurate readings than the TDS meters we used to use.

  40. finally i’m diving into using this! – i’m curious to know how sensitive the temperature of the sample taken is… we’ve been waiting for coffee to get to room temp (matching the temp of water calibration) – so i’m curious to know if you’ve compared day old samples to ones more fresh. this element of waiting for samples to get to room temp is the least enjoyable – i wonder if you prefer to brew various batches with various variables en mass, let’s say 5 or 10 at once. or if you’re strict on a one at a time method.

    surely more questions will arise once i keep testing this device out.
    tis wonderful though!


  41. Scott: There’s no need to wait a long time for samples to cool. Use one of those flexible plastic eyedropper/pipette thingies to transfer a few ml out of your cup into a room temperature demitasse. Place a cover on it if you wish (to prevent evaporation), swirl a bit, and within a minute or two the sample will be cooled close to room temperature. After you add the cooled sample to the well on your refractometer, wait another minute or two for the prism and the liquid to equalize in temperature. Then take your reading.

    The instrument is temperature compensated over a fairly wide range, but the prism and sample liquid must be at the same temp.

  42. Thanks Andy, this helps a lot. What is the average temperature of your samples… I’ve been around 70 F…

  43. Lately my samples have been in the range of 17-21C (63-70F), depending on the room temperature. But it doesn’t really make much difference; as long as the liquid and the refractometer are close in temperature when the liquid is poured on the prism, they’ll quickly equilibrate and the instrument will be able to get an accurate read.

  44. Cripes! No matter what I do I’m getting the same reading. I know for a fact I should be getting different readings and am even intentionally over/under extracting just to try and get a different read.
    1.33 1.33 1.33. . . I’m going back to read the manual, as I should but first I want to post a brief synopsis of my understanding and a couple of questions.

    1) clean w/ alcohol – do this between every sample
    2) calibrate with distilled water – also between every sample – holding cal and read buttons until END shows
    3) apply sample of coffee, let a couple of minutes pass so sensor and coffee equilibrate.
    4) clean, repeat.

    Onward I go to the manual – let me know if I’m F-ing anything up with my 4 steps.

  45. Scott,
    You are in the wrong mode. Your methodology is fine – simply scroll thru the modes until the top line shows battery power, temperature and nothing else. You are in either nD mode (refractive index) or TC nD mode – temperature corrected mode.
    hope it helps.

  46. Hi Scott:

    Tried calling you today on another topic, but you were buried with training, and apparently this problem. Sounds like your refractometer is in the nD (native) mode. Native Mode reads out the actual Refractive Index and TEMP of the sample/prism. You may use that mode, if you prefer, but you have to enter those values into either ExtractMoJo v2.0 or MoJoToGo for the iPhone, which uses those values to compute the % TDS.

    To read COFFEE TDS Directly on the refractometer, punch the “Mode” Button until you see nothing in the top-right display, which is % TDS. When in the Native Mode, Coffee ranges from about 1.3330 (pure water) to about 1.3356 (1.50% TDS) at approx 20 Deg C. You can use Native mode to read Espresso (1.3601 @ 20 Deg C = 15.0% TDS, w/o buying another instrument, by entering the nD and TEMP into the iPhone or eMoJo v2.0 APPs.

    Hope this helps, but feel free to phone me for more detail, left a number with your ADMIN staff. Best,


  47. Impressed by the timely responses!!! Surely, I WAS in the wrong mode.
    Shoot… I’ll add more to this shortly.

Leave a Reply