A Brief Interlude: The COM-100 TDS Meter

I've suspended my AeroPress testing for a short while because I've hit a snag in my brewing tests.  I use the COM-100 TDS meter, since it is a relatively inexpensive way to obtain figures for TDS and Extraction Yield in manually brewed coffee. I use it in addition to tasting, to establish whether I have found the correct brew parameters to create a great tasting coffee.

I already know from reading other blogs etc that there are accuracy issues with TDS meters. For example, the aren't actually measuring TDS. They are measuring Electrical Conductivity, as a proxy for TDS, and then using conversion factors to derive a PPM (parts per million) reading.  But anything is better than nothing... perhaps!

The problem I'm having is that Electrical Conductivity changes depending upon temperature. The COM-100 is supposed to be set to compensate for that, but I'm finding that I get completely different TDS/EC readings depending upon the coffee's temperature.  For example, at 68C the TDS might be 0.90%, whereas at 45C it might be 1.65%.  In coffee terms, that is a vast difference and renders the reading unusable.

I've emailed the manufacturer, HM Digital, to see if they have any suggestions.  In the meantime, I immediately feel like someone has stolen my security blanket! I haven't been using the TDS Meter very long, but it's amazing how quickly I seem to have become psychologically dependent upon it, not trusting my own palate.  Perhaps it's a good thing to have a break from the technology and rely purely on tasting for a while.

[See follow-on post here]