Refractometer readings much different than hydrometer why?

[beerguy1]

So, I thought I would get more modern and get a refractometer and start using it instead of my hydrometer. Plus lets face it it makes me look pretty technical as I gaze into the lens rather than look at a floating tube well perhaps not. So, I am getting about 5 degrees higher on the refractometer than I am with my hydrometer. It has been calibrated and it was tested on 65* product. It was a strong beer about 18 plato when I started and should be down to arouond 5 now which is what the hydrometer shows. Yes, it is brix but that is only a small correction factor. This is new to me any thoughts?

Thanks

[Thirsty_Monk]

Are you trying to measure fermenting beer? I do not have scientific explanation but Refractometer should be used in wort production only. May be someone else can chime in why.

[beerguy1]

Are you trying to measure fermenting beer? I do not have scientific explanation but Refractometer should be used in wort production only. May be someone else can chime in why.

Yes it is fermenting

[Scott M]

From Page 392 of Jean De Clerck Vol 1

Theory of Fermentation

"E-E'/E *100

Where "E" is the specific gravity before fermentation and E' the specific gravity after fermentation."

the result of the above provide the percent of attenuation.

Alcohol changes the refractive index of the wort. This is why using a refractometer to measure post fermentation wort does not provide us a meaningful number. The change in the refractive index due to the blend of alcohol, sugar and water in the final product skew the reading. Hydrometers are more immune to the effects of alcohol in the blend and provide a closer, but still not completely accurate; approximation of the remaining sugars in our beer. Always calibrate a refractometer with distilled water to 1.000, 0 Brix.

Here are some sources that help explain it better than I can..

http://www.brewersfriend.com/how-to-determine-your-refractometers-wort-correction-factor/

http://seanterrill.com/2011/04/07/refractometer-fg-results/

http://seanterrill.com/2012/01/06/refractometer-calculator/

[Junkyard]

as others said, dont use the refractometer for any liquid with alcohol in it. I think there is an equation on how to correct a reading with alcohol, but ultimately not worth it because you might as well just use a hydrometer for FG readings.

In our brewery, the refractometer is a good tool to use to get quick readings during mashing and lautering. when the kettle is full we usually switch to the hydrometer because you can always trust it.

[beerguy1]

Thats why I ask always someone smarter than I. Now I know

THANKS