Refractometer reading way off

[slash22000]

Just finishing up a brew, hydrometer is reading 1.054 OG (temperature corrected), my new ATC refractometer is reading 15 brix (1.062)?

I made sure to calibrate it with distilled water before using it (reading 0 brix exactly). It doesn't have a SG scale so I can't compare them. Is this just a matter of needing to calibrate it for wort or something? Or is the refractometer stuffed?

 

[Fat Bastard]

Take a sample and let it cool so all the break material and hop debris drops out then take another reading. Should be close to your hydro sample then.

 

[BeerNess]

Hydrometer readings at higher temperatures are very unreliable, and then the temp correction calculations can deviate your sample even more. I guess the only thing to do is check sample at 16-22°c with both again and see what you get? I'd be more inclined to believe the refractometer with a hot sample more than the hydrometer with the same sample. Also depends on what numbers you were expecting too!

 

[BeerNess]

Fat bastard has a good point about letting the crap settle out. My process is to draw a sample in one of those children's panadol or nurofen syringes and let it stand upright for a couple of minutes before drawing a sample from the little opening with the pipette that came with my refractometer.

 

[Pokey]

My refractometer with a hot sample reads high

 

[slash22000]

Alright, I let the sample cool down a bit more, let the crap drop out of it, measured again. Exactly 13.2 which correlates 100% with the hydrometer. :icon_cheers:

Had a brief panic attack there thinking the refractometer was DOA. One of my family members (they're all innocent, of course) snapped my last one in half. Not having a good run of luck lately. Cheers for the advice guys/gals.

 

[DJ_L3ThAL]

Surely with the small drops you place onto the cold refractometer glass and then spreading it out under the view plastic would bring the sample down to a reasonable temperature? Suggesting the break material would have a more considerable effect on accuracy?

Is it ok practice to use a pipette to extract a sample from the top of freshly boiled wort (spraying pipette with starsan to be safe of course) or is taking some from the keggle tap better?

 

[slash22000]

Something else I figured out is that you need to calibrate the refractometer as close to 20ºC as possible. If you calibrate it at 30ºC (for example, you live in Darwin), its accuracy is approximately dick.

I'm sure I knew that once upon a time but it skipped my memory this time.

 

[davedoran]

im having the same issue with my refractometer. Just bottled last night and checked fg with hydrometer and refractometer. Calibrated refractometer with distilled water.
Hydrometer read 1.014
Refractometer 1.024
Both tests were done at same temp (around 15 - 20 degs). After tested refractometer again with distilled water, 1.000

Im more inclined to believe the hydrometer in this as the OG taken and the FG are pretty much exactly what the recipe called up.
Will try cool some of the destilled water to 20 deg and calibrate refractometer again?

 

[DJ_L3ThAL]

Refract needs to be corrrcted for alcohol adter fermentation. There is a graph for this if you search (sorry on my phone).

From memory if your og was around 1.040 - 50 then a refract reading of 1.024 after fermentation would be around 1.014, I would not have bottled at 1.014 as might not be completely finished?

 

[davedoran]

Thanks mate. Will have a look for it. Was a pilsner. Expected fg was 1.013 and had been at 1.014 for 3 weeks. I think she was done

 

[DJ_L3ThAL]

Found it!

View attachment Refractometer Alcohol corrections.pdf

 

[davedoran]

Thanks,

Found this on the forum as well. Will try again with next batch and hopefully should be ok now.

View attachment Refractometer_Chart___During_Fermentation___Brix_to_SG.xls

 

[verysupple]

Hydrometer readings at higher temperatures are very unreliable, and then the temp correction calculations can deviate your sample even more. I guess the only thing to do is check sample at 16-22°c with both again and see what you get? I'd be more inclined to believe the refractometer with a hot sample more than the hydrometer with the same sample. Also depends on what numbers you were expecting too!

I think you are confused about how a hydrometer works/what it measures. As long as there aren't any bubbles clinging to the hydrometer and the sample is uniform (unstratified and isothermal) a hydrometer will measure the density very accurately at any temperature. The accuracy is limited to that of the printing of the scale and the thermal expansion of the glass, which is very small, especially in the temperature range we're interested in. The scale may or may not account for the themal expansion of the glass, but on cheap ones probably not as it will be so minute it doesn't matter.

The error only comes from the temperature correction equation/look-up-table which simply accounts for the change in wort density with temperature and estimates what the density of that wort would be at 20C.

NB: Specific gravity is just the ratio of the density relative to that of pure water at a given temperature. i.e. a SG of 1.050 is 5% higher density than water.