I increasingly been having serious doubts about the accuracy of the tools I use to try to measure gravity, so this afternoon I decided to set up a test to see what was most accurate. Ray Daniels' "Designing Great Beers" says that 1 lb. of table sugar dissolved in water to make 1 gallon yields a Specific gravity of 1.046. I scaled that down to 1 oz. of sugar and water to make 1 cup, which equals 1 lb. per gallon, and proceeded to test the Vee-Gee refractometer I recently purchased to replace the POS I originally bought, and an assortment of hydrometers I have collected.
The 1st test at a concentration that should be 1.046, the VeeGee gave a brix of 10.8 = 1.043 s.g., hydro #1 said 1.047, hydro #2 said 1.049, #3 said 1.050, #4 which I just bought as part of a 3 hydro set that is supposed to be super accurate as they each cover different gravity ranges said 1.049 [it covers a range from 1.000 to 1.070].
Next I heated the water to about 100*, added another oz. of sugar which should put the s.g. at 1.092, stirred thoroughly and cooled to room temp. The results corrected for temp were VeeGee - Brix of 20.5 = 1.085, Hydro #1 - 1.089, #2 - 1.089, #3 - 1.090, & #4 which covers a range from 1.060 to 1.130 said 1.088.
I then repeated the process with another ounce of sugar which should put the actual s.g. at 1.138 and tested all again. Results were VeeGee - Brix 28.4 = 1.122, #1 - 1.024, #2 - 1.124, #3 - 1.125, and the same #4 as the previous test - 1.124.
Needless to say I was anything but impressed. Clearly the refractometer was the least accurate instrument tested. Hydrometers #1 & #2 are the most accurate at most "normal" brewing gravities, and #3 is the most accurate above about 1.060 or so. The narrow range hydro's were generally the least accurate, even if they are the easiest to read. The refractor is now destined for the trash can, and the set of hydro's I just bought are going back to Midwest, unless they won't refund my purchase, in which case they're traveling with the VeeGee.
Maybe I am expecting too much from my tools, but this BEER for Pete's sake, not friggin horse-shoes, close isn't good enough for me.
Has anyone else found a more foolproof [or perhaps tool-proof] way to measure gravity? I look forward to everyone's input, including critique of my testing protocol [gotta luv them fancy words!].
Thanks.