SW refractometer to measure OG and FG of home brew

[piercho]

Dear chem-heads, I know some of you that are reefing are probably brewing as well. So...can I use my refractometer purchased for SW to measure the gravity of my brew? What's the best standard to calibrate to? That is, should I calibrate with RO/DI or should I calibrate at a typical OG of 1.050? TIA!

[Twistofer]

First read the instructions with your refractometer. It should tell you to calibrate the refractometer with RODI/Distilled water with an SG of 1.000.

Regarding your wort for home brewing, I use the good, old fashioned graduate cylinder and hydrometer. It's reliable and will not affect your refractometer. Using your wort in the refractometer may contaminate it and make readings in your tank inconsistent. They actually do make refractometers specifically for home-brewing, but it gets expensive.

[disc1]

A refractometer does NOT measure specific gravity. A refractometer measures refractive index. There is a direct relationship between specific gravity and salinity for seawater. This relationship between specific gravity and refractive index is not the same for wort. So the simple answer is no, you cannot use a seawater refractometer to measure the SG of your wort.

[disc1]

First read the instructions with your refractometer. It should tell you to calibrate the refractometer with RODI/Distilled water with an SG of 1.000.


If you want the maximum accuracy of the instrument to be around 1.000. If you want maximum accuracy at 1.026 then use a standard at 1.026.

The refractometer manufacturer does not know what you will be using his refractometer to measure. So if he told you to calibrate to some specific standard and you are measuring something far away from that then he would be telling you wrongly. So the best he can say is use RODI and that will get you in the ballpark. If you really want accuracy calibrate to something close to what you want to measure.

But that has nothing to do with wort. You won't be able to get any kind of accurate reading for your wort using a seawater refractometer.

There are refractometers out there that measure brix using refractive index. That will give you sugar content, which is what you want the specific gravity for. But even those are a bit dicey. Different wort (a light beer vs a stout vs a wheat beer) have different things in them affecting the relationship between refractive index and specific gravity differently.

If you want to use a refractometer for your wort and have any kind of accuracy, you'll need to use an internal standard. That means you make one measurement, add sugar, take another measurement, then do the math to figure out what the value was before the addition of the sugar.

Even with all that, for the beer you're much better off with the hydrometer. The relationship between SG and sugar content is much more reliable than refractive index.

[bertoni]

I agree that calibrating with RO or distilled water can be very far off:

http://reefkeeping.com/issues/2006-12/rhf/index.php

The PinPoint 53 ms/cm² conductivity calibration solution has been fairly reliable, and is a good choice for calibrating a refractometer. It should read 1.0264 on a properly calibrated refractometer.

[disc1]

Now a saltwater hydrometer would be another story. As long as it has a scale that fits the need it would be fine. Some might not go high enough to use for a really high gravity beer.