So, using the hydrometer correction calculator found here: Onebeer.net :: Homebrew :: Refractometer Calculator gives me incorrect results. For instance, when I type in my original brix (12) and my final brix (5) the reading says says my final gravity is 1.002 … however, the OG was ~1.050 and the FG is around 1.012 according my correctly calibrated hydromter (the refractometer is also correctly calibrated) … so what’s going on? Is that calculator off or WTF?
What was the final gravity reading of the refractometer?
In my experience, the correlation becomes less reliable the further you get from “normal” gravity and attenuation. At 1.050 and 76%, I don’t think that’s your problem though. I think high concentrations of dissolved gases also throw off the refractive index, so if fermentation is active that could be a factor. It tends to RAISE the Brix reading though, IME. 5°Bx is very low.
Just checking!
ProMash gives the same results.
could it simply be yeast in suspension skewing the results? Its fairly cloudy and, come to think of it, my IPA was pretty cloudy too and I got the wrong result.
Suspended solids shouldn’t have any impact on the RI. A cloudy sample makes it hard to read the line accurately. I don’t think you could get a ~2°Bx discrepancy from that though.
Things like this are why I went back to using a hydrometer for all FG readings.
see, its odd, my refracto is always spot on (after correction) with the hydro sample (I still take the hydro on occasion cause I like to taste how things are coming along ;D )
Don’t know what to tell you 
Hey blatz, I’ve been doing both to try to get some data points. Once I have 10 or so I’ll let you know and hopefully we can compare notes.
Here’s what you need to do Major. You have a pickup truck, right? (if not you can borrow mine) Take your refracto, and drive over it several times with your truck. Once I did this with mine, and went back to my hydrometer, I had no more issues with it. ;D
BRILLIANT!
Back to basic!!! ;D
I can’t understand how you guys can’t get a simple tool to work.
I’ve helped 2 other guys in my club acquire a refracto, set them up with the correction formulae and they are fine.
There is a thing called ‘user error’ ;D
We call it “operator error”. ;D Just kidding.
I like to use my refractometer during the mash and pre-fermentation because it’s quick and easy. However, I always use my hydrometer post fermentation because it’s most accurate and reliable at that point in the process.
I haven’t had any success using a refractometer post fermentation as you are also experiencing. Maybe there’s something we are missing, but I like to use my hydrometer because it’s dual purpose. I can quantify the result by measuring the gravity and qualify the result by tasting the beer from the hydrometer tube.
Another
Oh Snap! I really did laugh out loud…
I use the refractometer correction spreadsheet from morebeer. I can’t remember where I got the link to it though. It has worked for me and I have checked it several times against my hydrometer and its always spot on. I can’t remember the last time I used my hydrometer, except random double checking of the spreadsheet.