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…

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.

Vince

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.

Example:
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.

Ciao,

Vince Fedele
COO & Chief Technology Officer
George Howell Coffee Co

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:

Cheers,

Vince Fedele
COO & Chief Technology Officer
George Howell Coffee Co

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