Refractometer

[MichaelBrock]

I'm finding that my refractometer (an Ebay one w/ only a Brix scale) does not match my hydrometer. Today I calibrated both with DO water. For a beer with an estimated OG of 1.058 my refactometer read 1.053, the hydrometer 1.057. This was at 72 degrees F. I tried the measurement multiple times, with both, and got the same results each time. I have no idea why there is a difference but my trust is leaning towards the hydromter.

 

[passedpawn]

Hydros are calibrated (typically) at 60F. At 72, you'd need to add a point. I know that still makes it different than your refractometer.

Have you checked both with water?

 

[ClaudiusB]

I'm finding that my refractometer (an Ebay one w/ only a Brix scale) does not match my hydrometer. Today I calibrated both with DO water. For a beer with an estimated OG of 1.058 my refactometer read 1.053, the hydrometer 1.057. This was at 72 degrees F. I tried the measurement multiple times, with both, and got the same results each time. I have no idea why there is a difference but my trust is leaning towards the hydromter.

Nothing wrong with your refractometer.
I have never used a hydrometer except to get the Brix correction factor.
Refractometers are calibrated to read sucrose not maltose.
You need to run a few simple tests to get the offset for maltose, a onetime deal.

To read during and after fermentations requires a different offset.


Info from Promash

Brix Correction Factor:


A Brix refractometer reading is based on the known values for percentage sucrose solutions. However, wort contains many substances other than sucrose, and many of them have different refractive indices than sucrose. For this reason, it is necessary to use a correction factor to convert from a Brix refractometer reading of raw wort to the actual gravity of the wort. The literature suggests this factor is between 1.02 and 1.06, with 1.04 often used as a default value.

To determine your own, brewery-specific Brix correction factor:

(1) Take a hydrometer sample of unfermented wort.

(2) Measure its gravity with the most accurate, calibrated hydrometer you have. Do not forget to do the temperature offset calculations. (Alternative: use a digital density meter or pycnometer -- the idea here is to get a very accurate measurement of the actual SG / Plato of the sample.)

(3) Convert this value to Plato if you measured in SG.

(4) Using a zeroed refractometer, take the refractometer reading of the same sample.

(5) Convert this value to Brix if measured in RI or Zeiss units.

(6) Brix correction factor = Refractometer reading (in Brix) / Measured Gravity (in Plato) E.g., Refractometer reading = 13.1 Brix Measured gravity = 12.7 Plato Brix Correction factor = 1.0315

(7) Do this with several different samples and average the results. The literature suggests that the value should be consistent within a particular brewhouse.

Cheers,
ClaudiusB

 

[MichaelBrock]

@passedpawn: I did use both to measure a sample of RO water. The refractometer was calibrated to read 0 for the water. The hydrometer is right on the money after adjusting for temperature. I did adjust the hydrometer for temperature. That 1.057 is the compensated measurement.

@CladiusB: I wasn't aware of this! And my guess is that most other people aren't either. I'll make up some samples with DME and find the correction factor.

 

[klnosaj]

Nothing wrong with your refractometer.
I have never used a hydrometer except to get the Brix correction factor.
Refractometers are calibrated to read sucrose not maltose.
You need to run a few simple tests to get the offset for maltose, a onetime deal.

To read during and after fermentations requires a different offset.

I just discovered this for myself recently. Turns out BeerSmith 2.0 will help do these calculations for you. Now that I've calibrated the offset on my refractometer I find it's much, much, MUCH more reliable. So I retract my previous statement in an earlier post. It's refractometer for me all the way now.

 

[BigHead33]

Once you get the brix correction factor, what do you do with it? Do you add it or subtract it from the reading youre gettting on the refractometer?

Another question, can you use a refractometer to measure the SG of fermenting and fully fermented wort?

Thanks