Posted Wednesday, April 30, 2008

We are always on the lookout for people who can use the technology we have to offer and I came across a very interesting forum where users discovered a way to determine the strength of a coffee sample.

I contacted the author and he gave me permission to post the article here.

Subject: Measuring Coffee Strength With A Brix Meter Pal-1

- Alan Alder, Palo Alto CA.

Do you enjoy tinkering with grinding and brewing techniques?   Do you have about $270 to blow on your coffee hobby?   If not, this isn’t 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 he’d been using it for eleven years and that it was very accurate.   He also shared measurements he’d 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 I’ve 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 I’ve made:

1.5 Krups drip brewer with paper cone filter

2.1 Brewed coffee at Peet’s – 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:

1. The meters is temperature sensitive.   It can take about a minute for the sample to cool enough to give a stable reading.

2. 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 everybody’s favorite AeroPress temperature.

K increases to about 27 for a conventional espresso machine which uses both finer grind and hotter water.

It’s 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 .

Input water weight = brew weight + wet puck weight – dry coffee 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 isn’t as fine as claimed, the brew will be weak and the Brix low. All the cheap burr grinders I’ve tested fell far short of the formula, even on their finest setting.

As I said in the beginning, Brix isn’t for the casual barista.   But if you’re a Mark Prince, or Barry Jarrett or David Schomer, after you try Brix you’ll wonder how you ever got along without it.

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