Shouldn't this refractometer work for wort/beer??

I have a refractometer that I use for maintaining salinity on a saltwater fish tank. It seems like it should work for wort/beer also but when I tried to take a reading today of some fermented beer it read 1.040 and my hydrometer read 1.011 which is more like it should be.

My refractometer has a SG scale on it that goes from 1.000 to 1.070, it also has a PPT scale that is irrelevant to brewing.

Here is a link to the exact one I have. Premium Blue Refractometer - RHS-10ATC: Premium Aquatics

Refractometers only accurately (without correction) read OG, not FG.

Alcohol defracts light different than water. There are algorithms that can be used to correct the refractometer readings, but for the most part the concensus is that refractometers are great for OG - but next to worthless for FG.

One of these days I'll actually start taking FG's, and do that side by side with refractometer readings and see how close the algorythims are (google search - refractometer beer or refractometer homebrew and you should come up with a better explanation/ formulas)

1) the refractometer you linked to seems to be precalibrated for reading salinity SG - which is to say that a scale that reflects saline SG has been printed on this device which shows an optical change based on the refractive index of the medium that is applied to the measuring glass.
2) refractometers made for measuring sugar content are usually calibrated in Brix units (basically % sugar).
3) the deflection range that is visible on your refractometer is absolutely related to how much aquarium salinity causes a refractive index change this may be within or it may be outside the range that typical wort glucose solution causes (ie does saline % that is typically found in an aquarium, reflected on your scale - correspond with a typical glucose solution from 0-30 % that is found on a typical grape growers refractometer)?
4) its possible to make up a calibrated scale conversion by measuring out standard solutions of glucose (eg at 1 brix, 2brix, 4brix, 8brix etc) and seeing where they show up on your salinity scale - they you would just have to make up a conversion table.
5) Refractometers are used like hydrometers - the measure the remaining sugars in the wort. Sugars alter the refractive index of water much much more than alcohol - you can't measure the alcohol of a finished beer only the residual sugar( this is subtracted from the starting sugar to measure the final alcohol)

giligson said:

4) its possible to make up a calibrated scale conversion by measuring out standard solutions of glucose (eg at 1 brix, 2brix, 4brix, 8brix etc) and seeing where they show up on your salinity scale - they you would just have to make up a conversion table.

Click to expand...

This is exactly what I did to a Duo-Chek Coolant & Battery Tester.
The battey scale 1.100 to 1.400, great for big stouts. Divisions down
to 0.01, made by Cambridge Instruments Buffalo New York. Hey made in
the U.S.A.
The Coolant scale reads from +32*F for distilled water to -50*F.
Thru a known refractometer and different samples I made up my own
conversion scale chart. This is a temperature compensated Reichert unit
priced out at $129. Three scales, battery, Ethylene Glycol and a Propylene Glycol. I had to give it a try as it was given to me free new in box so no loss from the wallet. After purchasing 142 tons of batteries the driver had extra units. Speak and you shall receive. No internal light I can live without it works great outdoors or near a bright light indoors.

zanemoseley said:

I have a refractometer that I use for maintaining salinity on a saltwater fish tank. It seems like it should work for wort/beer also...

Here is a link to the exact one I have. Premium Blue Refractometer - RHS-10ATC: Premium Aquatics

Click to expand...

I use that exact model for measuring wort SG.

It's actually more accurate than the Brix models due to the smaller scale. But, like the you mentioned, the only disadvantage is you're limited to measuring an SG of 1.070. It's a tradeoff for better accuracy and convenience.

And, I believe you can find them cheaper on ebay...

I know this thread is a bit old, but came across it when searching for info on using a clinical refractometer that gives SG values (instead of Brix).

Anyway, you can certainly use these above the scale on the refractometer, just dilute your sample with water. You SG change will be linear....in other words, if you've got a sample that is off the scale, just dilute if 50:50 with water and double your refractometer reading of this mixed sample. If you are careful and use a small syringe to do your dilutions and mix thoroughly before measuring, it's accurate and repeatable. I use a 1 ml syringe to add 1ml of wort and 1 ml of water in a small test tube and aspirate/flush repeatedly to mix.