Refractometer question

[jason.loxton]

I just picked up a refractometer and am slowing integrating it into my routine. A calibration question: My water in Cheticamp is pretty mineral heavy, and the refractometer out of box read a touch off of zero as a result. The instructions are to calibrate to zero using distilled water, but it seems to me that whatever distorting effects my water will have pre-mash will carry over to the wort, making calibrating with the actual water I use more accurate. The Internet seems to be divided on this question. Checking my tap water calibrated refractometer against my temp adjusted hydrometer OG reading supports my approach making sense (at least in my single sample thus far). Thoughts?

Jason

[mr x]

Never really thought about that one....

Sent from my Nexus S

[chalmers]

How mineral heavy are we talking? It's true that the more minerals you have dissolved in the water, the higher the density, but I'm not sure if the difference is significant at drinking water levels.
I believe 1000ppm of total dissolved solids would be quite high. 1000ppm = 1000mg/L = 1mg/mL. Comparing that to pure water, you will get a specific gravity of 1.001.
However if there's something else in your water, that might account for the different readings.

All of that said, it makes sense to calibrate the refractometer using the water that will be used in the brewing process, as I'd be surprised if any of the brewing software accounted for minerals or anything but carbohydrates in their gravity calculations.

[jason.loxton]

My total dissolved solids are about 300 ppm, so the question is largely academic, I suppose. It just struck me as odd that distilled water is the preferred calibration point, when distilled water is not actually what one will be evaluating the concentration of sugars in.

[KMcK]

Of course if you boil the water you're concentrating the minerals so if the mineral content is significant enough to warrant concern pre-boil, it will be even more so syn- and post-boil. Perhaps the idea of calibrating against distilled water is to allow you to know what the mineral content is so that you can adjust your readings appropriately throughout the boil.