Refractometer / Hydrometer conundrum

[konkers]

I just transfered my Belgian Golden Strong (Brewing Classic Styles recipe) to a keg and checked the Brix with my refractometer. It came out to ~11* which puts it at ~1.040sg (ambient temp right around 20C). It tastes a bit sweet but I don't think 1.040 wort sweet. I dug out my hydrometer and got a 1.022 reading @ (15.7C/60.26F). I then went back and calibrated the refractometer and took another measurement. ~11*. Then I recalibrated then did it again and got ~11*. Any ideas why my measurements with the two could be so far off? Both devices are at least 3 years old and have been sitting unused in a garage for most that time.

Maybe I'll mix up a liter or 1.040 DME and taste compare.

[siwelwerd]

Yyou did plug your reading into a calculator/spreadsheet, right? Alcohol throws off refractometer readings. For example, if your OG was 1.080, a raw refractometer reading of 11 Brix corresponds to a SG of 1.022.

[Stinkfist]

Did you use the calculator to determine the Actual gravity?

Refractometers require an equation the calculate FG since the alcohol effects the value. You also need to use the same refractometer for the OG

[konkers]

Yyou did plug your reading into a calculator/spreadsheet, right? Alcohol throws off refractometer readings. For example, if your OG was 1.080, a raw refractometer reading of 11 Brix corresponds to a SG of 1.022.

Aha! That's exactly my problem. Odd that it was not mentioned in the refractometer appendix in How To Brew. With my original brix @ 20.9 that puts me @ 1.016 according to the Beer Tools calc. That's a much closer range. For the next couple brews I think I'll take readings with both and see how they track.

I quick chilled an carbonated up a few ounces and it tastes good with some nice strong clove flavor. I'll mark this one up in the success column.

Thanks!

[Ozwald]

There's also going to be a slight correction factor. Check unfermented wort on both a calibrated hydro & refract. Convert both to brix. Correction Factor = Refract / Hydro. Typically 1.02 to 1.08.

Refractometers were designed for use in the wine industry & are only capable of reading a pure sucrose solution accurately. Wort is very similar but not exactly the same as pure sucrose so the readings are going to be slightly off. If you do the above test on a half dozen or so different worts (light/dark & low/high grav will stray slightly, but not by much) you'll find a trend specific to your brewhouse & get more accurate readings.