Reichert R2 Mini Digitial Refractometer - Need to Test for Accuracy

(Julian Colman) #1


I just acquired a used Reichert R2 Mini Digitial Refractometer, that I need to test for accuracy. I acquired it for a low price, that the vendor agreed to refund if the unit is inaccurate or cannot be calibrated to be accurate. As I am a home enthusiast, I am prepared to take this this risk; I cannot currently afford to invest in a VST or other new unit.

Now Reichert sells a test oil, with a declared R value and temperature co-efficient, for accuracy testing. And it has excellent instructions on its website. However, they sell it for some $250 US. Any alternative suggestions for accuracy testing solutions? Any other ideas?

Even if this tests well, will the R2 Mini be sufficiently accurate, as a tool to improve my espresso extractions?

Fyi, the Reichert R2 mini technology apparently formed the basis of the original VST unit.

Any ideas or accuracy testing solution sources are welcome. I presume that all I need is the R value, as the temperature co-effecient can be determined through testing (as per the Reichert guide). Fyi, I saw a sugar based solution marketed for honey refraction testing, at a reasonable price and stated R value. Not sure if that would work.

Thanks for your help.


(Mark Burness) #2

Testing for accuracy (trueness) is beyond a lot of folk, worry less about this, concentrate more about checking precision. Accuracy is stated as +/-0.1% TDS, less than a quarter of a % EY at 1:2 ratio.

Make a shot, draw up a sample into the syringe as per instructions, but draw up a larger amount. Expel a sample through the filter & take a reading. Keep the syringe capped. Give it a shake, then expel a new sample through a new syringe, Repeat.

What variation do you get between readings of the same sample?

(Julian Colman) #3

Thanks for taking time to reply, Mark. Most appreciated.

(Austin Averill) #4

I’d love to hear what you come up with. I’ve been interested in getting an alternative VST refractometer myself. I hope this Reichert R2 Mini is able to deliver. Would you be willing to post your precision test?

(Mark Burness) #5

The Reicherts that read in coffee %TDS were sold by VST. Otherwise, you’re looking at readings in nD or Brix.

(Julian Colman) #6


I spoke to Reichert and they said to calibrate the unit with distilled water, and provided specific instructions on that.

With regards to testing, to make sure my just purchased but used unit is accurate, they suggested making up a solution of 10% sugar and 90% hot distilled water by accurate weight, then dissolving the sugar in the water. Then allow the water to cool to 20 C and then have the unit display the Brix, which should match the formula calculated Brix for this sugar solution. Fyi, the unit automatically adjusts for temperature, if you allow time for the sample and the glass cell reach equilibrium.

Fyi, I have the R2 Mini that has the coffee cup image on the front ( catelog 13940010 SN 01880-0409), so I suspect that the unit is accurate enough for coffee TDS testing. I welcome any comments on this.

And lots of questions, as I’m a newbie at this refractometer stuff.

What I am unsure about is how to test an espresso sample, to obtain a TDS percentage. I need step by step guidance. Any info or directly useful links would be gratefully appreciated.

I understand that one has to pass the espresso coffee though a filter, to remove undisolved solids. But the R2 does not come with one. What spec of filter should I use and where can I procure it at reasonable cost?

And do I need to cool the coffee to 20c? I understand that I should in any event allow the coffee temp and the prism temp to equalize.

How do I adjust for temperature? If so, how? Or is this automatic?

How do I end up with a TDS % reading? Will the unit display this or must I calculate? If so, how?

Sorry for the many questions. Any help would be gratefully appreciated.


(Mark Burness) #7

Here are VST’s instructions, they also sell the syringe filters (you may also have an agent in your country)…

(Julian Colman) #8

Thanks Mark! Thats just what I needed!

The unit pictured looks identical to the used one I just bought. So do I actually have a VST unit? Don’t quite understand the difference between the VST and Reichert R2 Mini Coffee models. Sorry for the dumb questions.

(Mark Burness) #9

As I understand it, the R2 Mini reads in nD (refractive index) & BRIX scales. The Coffee/Espresso models sold by VST read in coffee %TDS.

VST probably have a brochure/instructions if you e-mail them.