Measuring Coffee Strength

coffee refractometer

When I started roasting coffee, I became more concerned than ever with a mountain of details related to brewing. After all, how could I judge the quality of my roasts if I couldn’t be assured that I was brewing coffee under optimum conditions? This wasn’t a question for me previously, since I was only brewing for myself and it was always on my espresso machine where I had total control over the brew time, grind fineness, brew temperature, pressure, weight of the grounds, and so on. Once my machine was “locked in” all I needed to do was make sure my 20 grams of coffee extracted 45 grams of espresso in about 25 seconds.┬áBut when you are sending beans off to places unknown, to be brewed under conditions unknown, one needs to level up their understanding of coffee under myriad brewing conditions.

To understand brewing, there are 4 tools that I consider essential. First, you need a way to measure your ground coffee, both its structure and its weight. This comes in the way of sieves and scales. When I need to measure coffee grounds, I use a set of Kruve sifters with a full range of screens, from 1,400 microns to 200 microns. For a scale, I look for digital scales that can measure grams and ounces with an accuracy to .01 grams and a maximum weight of at least 500 grams. The other tools include a digital thermometer and a refractometer. The digital thermometer can be a kitchen thermometer, or you can get fancy and use an industrial model that accepts multiple probes. I have one that will measure 4 temperature sources simultaneously. It allows me to geek out and measure the temperature of the water hitting the grounds, the coffee leaving the basket, and the coffee inside the carafe through the duration of the brew cycle. Okay, I’ve only done this a couple times, but it’s elucidating, all the same. The main temperature to know is the water temperature as it’s hitting the grounds.

The last, and perhaps most inaccessible piece of equipment is a digital refractometer. This is a device that will tell you how strong your coffee is. You might think “oh, I can taste it and tell whether it’s too strong or too weak”, but that does’t tell you whether your coffee is 98.5% water and 1.5% coffee or 98.75% water and 1.25% coffee. That is the purpose of a digital refractometer.

My first refractometer was an Atago PAL-1. These are made in Japan and the PAL-1 is a portable general purpose refractometer that measures BRIX (a measurement of sucrose in a liquid) on a scale from 0%-53%. Since this is a fairly large range, the level of precision is .1% Brix. Coffee is measured in TDS, or total dissolved solids. To correlate Brix and TDS, you can take the Brix measurement and multiply it by .85 and that is a close approximation of TDS. I soon discovered that the PAL-1 is not accurate enough for coffee. The difference in taste between 1.26% and 1.34% TDS is substantial, and in the case of the PAL-1, both of these readings would be the same.

I moved on to the Atago PAL-COFFEE, which calculates TDS for you and has an accuracy of .01%. This has proven to be a much more reliable device, and with it, I can now check my coffee strength with every brewing method I employ. It allows me to develop consistent standards so that I can brew the same coffee as a pour-over, drip, Aeropress, or k-cup and achieve the correct strength by manipulating grind, quantity, temperature, or time.

VST introduced the first coffee refractometer in 2011 and currently sells an updated model at a starting price $729. For coffee professionals, this is the industry standard. For those on a tighter budget, Atago is a reliable company and has been in the refractometer business for quite some time. The Coffee versions of their refractometer, particularly the PAL-COFFEE (TDS) sells for about half the price of the VST. A search on sites like eBay and Alibaba will turn up other Brix refractometers, some at considerably lower prices, but they only have a reporting accuracy of .1%, which isn’t good enough for coffee.

 

 

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