Refractometer TDS% Error Message When Testing Espresso

I recently acquired a Reichert R2 Mini Coffee Refractometer. It is the version developed by Vince Fedele when he was with Howell, in collaboration with Reichert. I calibrated it and tested it with a defined sucrose solution. It has decent accuracy. However I get an “Error 12” when testing espresso when in TDS% mode. Now I am currently not filtering the coffee, as I read articles that said this did not make a difference in results. I’m not for or against filtering; just wanted to give it a try. Anyway, Error 1 is “no sample present” and Error 2 is “insufficient sample”. Any ideas on the cause, or solutions?


Interesting / curious that I do get refractive index mode (Nd) results, in both standard and temp adjusted mode. But Error 12 for TDS%. Any idea why? Solutions? See initial post above.


Apparently I could convert to Nd to TDS%, if I had V2 of MojoToGo or associated Iphone app. VST Coffee Tools does not seem to have that utility. Can I obtain that v2 software / app anywhere?)

For those that are interested, the VST Technical Support team was most helpful, and solved my issue.

The short answer is that there were three versions of this device: one for poured coffee, one for coffee/espresso (weak espresso) and one for espresso. Each had a TDS% limit. Mine is a coffee/espresso device with a 9.9% TDS limit.

The solution is to dilute my sample shot with distilled water by a specifIed proportion, best using a scale accurate to 0.01g, then test and then adjust the resultant TDS% using the following formula: Mass(i) * %(i) = Mass (f) * %(f) and solve the equation for %(f), where Mass(i) is the weight of the diluted sample and %(i) is the TDS% of the diluted sample.

For example, weigh the shot and add an equal amount of distilled water. Then test the TDS% and multiply that x 2.