Refractometer vs Hydrometer - different readings. Which one to trust?

[luckybeagle]

I brewed a Belgian Blonde with WY3522 10 days ago.

I took a post-boil gravity reading at pitch temperature (67F) with my hydrometer. It was 1.068. I tested the same sample with my refractometer, which was 16.6 BRIX (also 1.068). Recipe goal was 1.072 but I slightly oversparged. No big deal.

Today I took a sample of my beer and my hydrometer says 1.012. My refractometer said 7.1 (which is 1.004). I am using the Brucrafter calculator, which takes the presence of alcohol into account.

If I trust my hydrometer, that means I achieved 82% attenuation, which seems about right for this yeast. If I trust my refractometer, that's 94% attenuation, which does not seem right.

The beer tastes great and finished, but this number discrepancy has me concerned. Refractometer reads 0 with plain old water from the tap, so I know it is calibrated. Should I toss this thing, or shop for a new hydrometer??

 

[IslandLizard]

Hydrometer, always!
Make sure your sample is degassed and close to the calibration temp, usually 60°F.
CO2 in solution can literally elevate your reading.

Refractometer calculators are an approximation, and there are some unknown variables. One being the "wort correction factor."
I use this one:
Refractometer Calculator - Sean Terrill

 

[Lorne Lemaire]

refractometer is very handy prior to fermentation, during and after fermentation hydrometer only for me!

 

[Nate R]

I have cheap versions of both...
I find the margin of error from me reading it is abouy equal- i can guess closely to where either on reads, but not perfect on either one.
I appdeciate the much smaller sample needed for the refractometer. I feel i can do 3x the readings with it and still save more wort/beer vs. a hydrometer. Then i feel better about taking an average of the multiple readings.
I want a digital model like a Hannah or Paar, but no way i can justify that amount of dough. If i am gonna spend the money i would rather have more fermentors and or temp control gear.

 

[luckybeagle]

Thanks fellas! Since I see consistency between hydrometer and refractometer readings on brew day, I think I'll do exactly what was mentioned above and switch to hydrometer for carboy samples during/post fermentation. I do like that I can get a good preboil reading within just a few minutes of puling a ~150F sample from my BK using the refractometer before firing up the element. I've found the temperature adjustment calculators for hot wort samples to be a little off when I'm using a hydrometer (e.g. 120F sample, 60F calibration might calculate out at 1.050, but actually be 1.046 once the sample cools).

I hate wasting so much beer to fill up my hydrometer from the carboy (and also worry about double/triple dipping and the slim chance of infecting the beer), but maybe I should just stay out of the carboy for longer and only take 2 readings as things appear to finish up in fermentation.

 

[Nate R]

Thanks fellas! Since I see consistency between hydrometer and refractometer readings on brew day, I think I'll do exactly what was mentioned above and switch to hydrometer for carboy samples during/post fermentation. I do like that I can get a good preboil reading within just a few minutes of puling a ~150F sample from my BK using the refractometer before firing up the element. I've found the temperature adjustment calculators for hot wort samples to be a little off when I'm using a hydrometer (e.g. 120F sample, 60F calibration might calculate out at 1.050, but actually be 1.046 once the sample cools).

I hate wasting so much beer to fill up my hydrometer from the carboy (and also worry about double/triple dipping and the slim chance of infecting the beer), but maybe I should just stay out of the carboy for longer and only take 2 readings as things appear to finish up in fermentation.

Be careful with hot wort on a refractometer- I have read and experienced that because it is so small a sample, there is a lot of evaporation from when you get the sample to when you can read it.
Lots of tips around on how to correct it, but fyi. ymmv

 

[IslandLizard]

maybe I should just stay out of the carboy for longer and only take 2 readings as things appear to finish up in fermentation.

That's a wise thought. Keep the yeast happy so she can do her job, and finish out around where you expect her to. There's not much you can do about it if she doesn't.

 

[smata67]

Not sure if this applies to all the refractometers out there, but I have found that on my cheapie one, the "SG Wort" scale is flat out wrong. I go by the Brix scale only and enter into the online calculators available and this matches up within .001 with my hydrometer readings. If you go by the SG Wort value read straight off the refractometer, it is significantly lower, at least in the range that I have been using it for. For example, I read 18.8 Brix and measure 1.079 with my hydrometer. Calculators estimate SG at 1.078. If you read the refractometer's SG Wort scale, the corresponding value for 18.8 Brix is 1.073. The error is even larger when reading in the FG range. So use the Brix scale and ignore the other one.

 

[BrewMan13]

Always trust the hydrometer if they disagree. Refractometers measure the amount of sugar in solution, but there are many other variables in wort, so you need to account for a correction factor; for me it was 3 gravity points, but since I broke my refractometer, it's hydrometer all the way going forward.

 

[Brooothru]

refractometer is very handy prior to fermentation, during and after fermentation hydrometer only for me!

Beginning = very accurate
Fermenting = approximation, at best
After clearing/settling = almost always within 1-2 gravity points of each other, assuming samples are degassed and close to calibration temperature (also, "alcohol present" calculations are applied by the calculator software).

As long as FG has been reached and temperature is close to calibration temperature (and sample is degassed), I'm almost always within the margin of error between the hydrometer and the refractometer. Disclaimer: my 70 year old eyes can discern the 0.10 gradiations of refractive indices better than the point at which the menisci cross the marks on a hydrometer. Nevertheless, I'm almost always less than 1 gravity point difference between the two at FG, with both calibrated with distilled water @ 60F/15C.

That said, anything between OG and FG is "advisory in nature only" when using the refractometer, but it's close enough to let me know when to rack wine or spund beer. Also saves me the torment of dumping a cup of precious beer/wine instead of 1ml sample with each mid-fermentation measurement.

Brooo Brother