Posted Mon Jan 16, 2006, 4:55pm Subject: Measuring Coffee Strength With A Brix Meter
Do you enjoy tinkering with grinding and brewing techniques? Do you have about $270 to blow on your coffee hobby? If not, this isnít for you. But if so, read on.
While developing the AeroPress, I needed a method to measure brew strength. I first tried the SCAA Total Dissolved Solids (TDS) meter but found the results inconsistent. I called SCAA and discussed it with their Technical Director, Joseph Rivera. I mentioned that I was an electronics engineer and thought that the TDS meter, which is simply a conductivity meter, was too sensitive to small variations in saline content of the water or the finished brew. Joseph agreed and said that he had heard that someone was using a Brix meter.
A Brix meter measures index of refraction and is normally used to measure sucrose level of liquids such as juice or wine. A Google search for Brix and coffee measurement came up empty, but I decided to give it a try and bought a $270 Atago PAL-1 digital Brix meter. It turned out to be the answer to my needs.
To measure brew strength with a digital Brix meter you put a few drops of brew on a small glass window and press the button. Voila! A reading appears. No calibration baths or other annoyances. It fits in my pocket and I can take it from my lab to a coffee shop whenever I wish.
After using Brix for about a year, I took it to the SCAA Convention in Seattle last April and showed it around. One of the first people I showed it to was Joseph Rivera. A few months later, he bought one himself and is now a confirmed Brix user. He also told me recently that his dehydration instrument verified that Brix is far more accurate than the old conductivity meter they sell.
Another person I showed it to was Randy Pope of the Bunn Technology Center. Randy pulled out his own Brix meter and told me that heíd been using it for eleven years and that it was very accurate. He also shared measurements heíd made to correlate Brix to Total Dissolved Solids as measured with his dehydration instrument. He found that 0.85 x Brix equals the percent Total Dissolved Solids (TDS).
The SCAA recommends 1.25 percent TDS for ordinary brewed coffee. That corresponds to 1.47 Brix, which the meter rounds to 1.5. There is no standard for espresso, but Iíve measured hundreds of shots and find that most are in the ranges from about 3.4 for pod and capsule machines to about 7.5 for professional pulls. Here are some measurements that Iíve made:
1.5 Krups drip brewer with paper cone filter 2.1 Brewed coffee at Peetís Ė Los Altos, California 3.4, 3.6 Nespresso capsule brew 3.7 Victoria House concentrate 4.8 Starbuck's, Los Altos 4.4 Filtron cold-brewed concentrate SCAA booth 4.9 Solis automatic at Baratza SCAA booth 5.2 Ken Davids' Saeco Vienna (Summer 2004) 5.3 Ken Davids' Saeco Vienna July 25, 2005 5.9 An old Italian lever machine 5.6 Rancillo booth at SCAA 7.3,7.4 Pasquini Riviera machine 7.5 Peet's, Palo Alto, California 20.6 Cafe' Vivace, Seattle
The last reading is unusually high and the product of espresso-guru David Schomer, who clearly likes a very intense shot.
My own taste buds prefer about 7.5 for straight espresso but I make it stronger when making a shot that will go into a latte. Of course I brew my shots in an AeroPress, which can make any Brix I want, even up into the twenties.
Here are two tips on Brix measurement of coffee:
The meters is temperature sensitive. It can take about a minute for the sample to cool enough to give a stable reading.
Brix is primarily a method of measuring sucrose level, so there must be absolutely no sugar in your sample.
After measuring the Brix level of hundreds of samples, I developed this formula:
Brix is approximately equal to K times (coffee weight) / (water weight)
K equals about 23 for an AeroPress using fine drip grind and 175F water -- which is everybodyís favorite AeroPress temperature.
K increases to about 27 for a conventional espresso machine which uses both finer grind and hotter water.
Itís easy to weigh the input coffee and input water with an AeroPress, but more complex with a conventional espresso machine. Barry Jarrett asked me how I do that. Here is my answer:
Weigh the empty portafilter.
Add and tamp coffee, weigh it again and subtract empty portafilter weight to get dry coffee weight.
Weigh the output cup.
Pull the shot.
Weigh the cup of brew and subtract empty cup weight to get brew weight.
Weigh the portafilter containing the damp puck and subtract empty portafilter weight to get wet puck weight .
You can also use a formula based on coffee weight / brew weight. That's simpler with a conventional espresso machine and the formula is about:
Brix ~ 18 times (coffee weight) / (brew weight)
I also find Brix to be an excellent tool for evaluating grinders. If the grind isnít as fine as claimed, the brew will be weak and the Brix low. All the cheap burr grinders Iíve tested fell far short of the formula, even on their finest setting.
As I said in the beginning, Brix isnít for the casual barista. But if youíre a Mark Prince, or Barry Jarrett or David Schomer, after you try Brix youíll wonder how you ever got along without it.
Don't different beans have different amounts of sugar in them as a result of the roasting process (and the green bean itself)? Wouldn't this make readings from different sources (ie. Peets vs. Starbucks vs. Vivace) not comparable? Or is the difference in sugar content from bean to bean (and roast to roast) not enough to cause variability when comparing two grind and brew techinques?
counting Senior Member Joined: 8 May 2005 Posts: 823 Location: Baltimore, MD
Posted Tue Jan 17, 2006, 4:03pm Subject: Re: Measuring Coffee Strength With A Brix Meter
Of course you realize that your post flirts with standing the entire Geek community upon its collective ear?
Seriously, this is really interesting. I've never used a digital meter. Do you have any comment about the utility of optical versions? Good ones have temperature compensation.
It's been a while since I've used these, but if I remember correctly, the user might need more than one optical meter to cover the range you address - I'm not positive about this, do you know the answer? Also, can you say something about the current cost of useful optical meters vs. digital. I guess my question is, would you discuss the positives and negatives of optical vs. digital for geeks who want to know what the alternatives are?
Coincidentally, Alan, yesterday I attended a demonstration of the Clover coffee brewing system at Gimme Coffee in Ithaca, NY. I brought along a few gadgets, including an inexpensive handheld (analog) refractometer. It's interesting that you measured Peet's brewed coffee at 2.1, because that's just about what we measured in one cup coming off the Clover brewer.
The particular instrument we used yesterday was bought new on eBay for only $29. For drip coffee, a refractometer with a 0-10 brix scale is probably ideal. For espresso, a 0-30 is probably best. One of these would be a good way for a curious hobbyist to dip their toe in the water (so to speak).
I tested the Atago PAL-1 about six months ago (but on soymilk, not on coffee). The obvious advantage is that it gives an unequivocal digital reading that is not subject to interpretation, whereas six people using the same inexpensive analog handheld refractometer may sometimes get six different readings. But the Atago was easily thrown off by high levels of oil and undissolved solids in the sample, so we returned it. I wonder about the durability of the Atago; it was not a particularly robust design (of course, the $29 jobs don't seem very durable, either). I have one high quality handheld optical refractometer which has been in use for 25 years. It's fogged up a bit and is therefore harder to read, but it still gives the same answer as the new ones.
Certainly in espresso a significant part of the mouthfeel is in oils and undissolved solids, which the refractometers cannot read. Although you didn't say it, do you feel that the undissolved stuff probably is extracted in about the same proportion as the soluble stuff? If so, the refractometer would still be fairly accurate in assessing espresso "strength." We don't know this for sure, though.
The formula that you gave for converting brix to TDS is very handy, thank you. BTW, my espresso measures in the 12-15 brix range. Boy, that Schomer uses a lot of coffee and pulls a mighty short shot.
Brix is primarily a method of measuring sucrose level, so there must be absolutely no sugar in your sample.
My experience has been that these kind of numbers are useful in comparing and standardizing observations with other people when you can't be in the same room together. Otherwise, I'd offer the usual disclaimer that one can get so caught up with the measurements that one gets distracted and forgets to really taste the coffee (been there, done that).
Although I have the refractometer in my "stuff" drawer, I hardly ever use it. I honestly don't think too many people are going to find it helps them to improve their espresso. How has it improved yours (assuming what you make is espresso)?
Posted Wed Jan 18, 2006, 12:11am Subject: Re: Measuring Coffee Strength With A Brix Meter
I'll try to respond to the blizzard of comments here.
First of all, I too worried that the different levels of natural sugar in coffee might affect the readings. However after more than a year of use on a wide variety of beans, and discussing this issue with Randy Pope of Bunn, I'm now convinced it's not of concern. My warning was, of course, to not ADD sugar before taking your sample.
Regarding analog Brix meters. I've never tried one. My PAL-1 lists for $295 but Nova-Tech discounts it to abut $270. It has a range of 0 to 50 and reads Brix to the nearest 0.1.
When I met Randy Pope at SCAA, he had a Link DRBS-300 meter. It was larger than mine. We compared readings on the same batch of brewed coffee and the readings were identical.
My PAL-1 is temperature compensated. But the compensation has a limited range. So when I first put a few drops on the window it reads several tenths low. After about a minute it stabilizes. The reading will stabilize quicker with a fewer number of drops. Any amount sufficient to cover the glass window will stabilize at the same reading.
Yes that Cafe Vivace' shot was VERY short. It barely covered the bottom of a tiny ceramic espresso cup and was probably less than a half ounce of brew. The barista told me he used 20 grams of coffee to make it. Ristretto with a capital R!
Regarding durability. Mine has traveled a lot and still works like new.
I hope I've covered it all, but if not let me know.
Crit Senior Member Joined: 25 Jan 2006 Posts: 5 Location: GlobalMegaNationalBeverageCorp, Inc Expertise: Professional
Espresso: Proprietary Grinder: Proprietary, Rossi
Posted Wed Jan 25, 2006, 7:33pm Subject: Re: Measuring Coffee Strength With A Brix Meter
I have a comment to add w/ respect to using Brix as a metric of how much Goo (flavor, solids, potency, etc) is in your coffee. What we all mean when we talk about Brix is the % Dissolved Solids, and I think we do a disservice by confusing Brix with it. People who make soda pop and candy are concerned with Brix, but that's just the percentage of sucrose in a sample.
If you had twice as much "Goo", can you be certain that a Refrac meter will tell you that it looks like it's got twice as much sucrose (since that's what it's looking for evidence of)? The answer, from my experience, is no. While using Brix makes for a good approximation and allows you to quantify who makes the strongest coffee, it's not foolproof. I'd suggest that if you really want to compare apples to apples that you use a densitometer to compare specific gravity. This is especially important if you have considerably different roasts, because you can't count on two similar extracts producing the same refractive index. One would look stronger to a Refrac when it might not be.
Analog refractometers DO provide a cheap and portable way of comparing coffee on-the-spot at the table, but I'd suggest a different approach if you really want to find that perfect blend, and you want to ever reproduce it.
Posted Wed Jan 25, 2006, 9:59pm Subject: Re: Measuring Coffee Strength With A Brix Meter
I too was skeptical of Brix. I'll bet I was even more skeptical than you. But using one for a couple of years and my conversation with Randy Pope at the Bunn Beverage Technology Center have changed my mind.
Randy told me that he verified the accuracy of Brix on coffee with dehydration tests. That is to evaporate the water and weigh the residue.
Joseph Rivera the SCAA technical director also has a dehydration tester in his lab. He told me that Brix is much more accurate than the conductivity meter which SCAA sells as a TDS gage. He said the conductivity meter reads 30% higher than true.
counting Senior Member Joined: 8 May 2005 Posts: 823 Location: Baltimore, MD
Posted Thu Jan 26, 2006, 12:33am Subject: Re: Measuring Coffee Strength With A Brix Meter
Alan's comment about the TDS being a conductivity meter is true, and that's the reason its results are misleading (erroneous). A conductivity meter responds to ions such as the hydrogen ion from an organic acid. It's very sensitive to ionized bases, acids, salts, and the conductivity of each combination of ions is different. A conductivety meter presented as a TDS meter is pre-calibrated for some particular use, such as testing water hardness, in which case it would expect to be measuring the conductivity of a solution of calcium and magnesium salts, hence the error.
Alan's use of the Brix meter is entirely legitimate. True, a Brix number indicates sugar concentration, but Alan is legitimately using it to give us numbers which, though not indicitave of sugar concentration, do reliably indicate differences in brew strength. He might just as well give us index of refraction numbers - he chose to use Brix numbers.
Refractometer readings are used in exactly this way in the quality control of wine (maybe beer for all I know?), anti-freeze (ethylene glycol, propylene glycol), and many other applications.
The point about roast might be relevant at the 0.1 sensitivety level of Alan's machine, I don't know. I suspect that roast differences would cause only small differences in readings, but I don't have experience in this application.
Enkerli Senior Member Joined: 1 Aug 2004 Posts: 722 Location: Montreal, Qc Expertise: I love coffee
Espresso: (At cafés, not at home) Grinder: Hario hand grinders Vac Pot: (Moka Pot) Bialetti Brikka Drip: Steep and release pour-over Roaster: iRoast-2
Posted Sun Mar 26, 2006, 10:29pm Subject: Refractometers
Ah! Nice thread! Saw it thanks to Ken's mention in this thread: "Re: Brikka Notes (26 March)" As it's a few months old, this might be a case closed. Still, thanks Alan for the measurements and constants. Would really like to take measurements of moka pot coffee with different coffee to water ratios. In terms of mouthfeel, it doesn't seem to be directly proportional to the coffee/water ratio (i.e., you can feel more body with some lower bean/water ratio). But mouthfeel is as subjective as taste so a measurement would be nice. A quality digital Brix meter is out of my league but an inexpensive optical refractometers that does 30 % Brix would also be useful for (beer) homebrewing. In beer, sugar percentage correlates directly with alcohol content (original gravity - final gravity/K). Then, the gravity/density of the fermented beverage correlates with residual sugars which have a lot to do with body and mouthfeel. Hadn't noticed the inexpensive refractos on eBay. Thanks!
treston Senior Member Joined: 15 Aug 2006 Posts: 10 Location: Ireland Expertise: Just starting
Posted Wed Aug 16, 2006, 7:50am Subject: Re: Measuring Coffee Strength With A Brix Meter
Don't different beans have different amounts of sugar in them as a result of the roasting process (and the green bean itself)? Wouldn't this make readings from different sources (ie. Peets vs. Starbucks vs. Vivace) not comparable?
If one bean has far more sugar in it then this will show up in electronic TDS and dehydration tests too, so there is no problem (or the same problem if you look at it that way).
I have a comment to add w/ respect to using Brix as a metric of how much Goo (flavor, solids, potency, etc) is in your coffee. What we all mean when we talk about Brix is the % Dissolved Solids, and I think we do a disservice by confusing Brix with it.
The Brix scale is simply specific gravity (SG) multiplied by a factor. Since taste aroma etc cannot be really tested and compared, people use whatever measurable scientific factors they can. These refractometers are measuring the refeactive index of the liquid, some are given a Brix scale, but can be used for TDS on other substances, just like a thermometer in F can be used to measure in C. The result of a refractometer is supposed to be called "refractometric dried substance" RDS. The SCAE are promoting the idea of a "golden cup", i.e. a rating given to coffee shops, it means they have produced coffee which fell inside the "ideal" range, part of this range is the TDS other factors are also measured. Of course coffee in this "ideal" range could be disgusting. I see it somewhat similar to accredited quality systems like ISO9000, you can make very low quality products but as long as your procedures say you do then you pass the test.
A conductivety meter presented as a TDS meter is pre-calibrated for some particular use, such as testing water hardness, in which case it would expect to be measuring the conductivity of a solution of calcium and magnesium salts, hence the error.
The SCAA sell calibration fulids at 1200ppm which are intended to replicate the salts found in coffees. (I also find the electronic TDS readers to fluctuate a lot)
What do people think of hydrometers? this would be my preferred way of measuring, though you do need a certain amount of liquid for it to float in.
What nobody has mentioned is density of the water, i.e. 1 litre of water @ 100C when cool will have a lower volume by about 3%. People are usually cooling for these TDS readings so the results are higher than if it was still hot.
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