Refractometer Question

[HopSong]

I'm sure this is a rhetorical question(s).

I know you have to calibrate/check the accuracy of a hydrometer.. but..

What about a refractometer. I just purchased a second one from MoreBeer and it is in SG rather than Brix. I've never thought of checking them against a hydrometer that seems accurate using distilled water.

If so, do I check it with distilled water?

I'm guessing there is no way to correct them.. as there is no way to calibrate a hydrometer. Just have to know how far off you are and compensate?

 

[Dan]

I can't speak for every refractometer but the one I use, and it isnt an expensive one, has an adjustment screw. Measure distilled water and it should be reading 1.000. Adjust as required. Only takes a minute or less. I usually only do it once a brew session/use. If the refractometer isn't temperature compensated that is something to take into account but most of them are, even my cheap one.

 

[Dan]

If the below is the refractometer you bought from more beer SG/BRIX scale, AutoTempCompensated. It is adjustable. Directions in the following MoreBeer link.

http://morebeer.com/products/brewing-refractometer-dual-scale.html

 

[HopSong]

Tnx Dan.. That's the one.

 

[Dan]

You're welcome HopSong. Keep in mind alcohol will throw off the refractometer's accuracy. At the bottom of the write-up they provide a calibration method to compensate for that error.

Refractometers are great gadgets. Quick readings, no need to wait for the wort to cool and only drops are used not ounces. I've all but stopped using a hydrometer.

 

[mtnagel]

Just to let you know, that scale is off. Use a brix to SG conversion calculator and enter a brix value and check to see if it matches what you see in the refractometer.

According to brewersfriend.com, 30 brix is 1.1292, but looking at the picture on the moorbeer website, it looks like it's closer to 1.117.

Mine is the same way, so I checked it with some sugar solutions and I found out that my brix scale is accurate, but the SG scale is off. So now I only use brix and convert to SG with the conversion when necessary. Here's where I talked about measure sugar solutions with it.

 

[Bearfoot]

My refractometer is also auto temp compensated, but I've noticed it needs up to two minutes for the reading to stabilize with a hot sample. Many of my readings have been off while I've gotten used to it.

 

[Dan]

Just to let you know, that scale is off. Use a brix to SG conversion calculator and enter a brix value and check to see if it matches what you see in the refractometer.

According to brewersfriend.com, 30 brix is 1.1292, but looking at the picture on the moorbeer website, it looks like it's closer to 1.117.

Mine is the same way, so I checked it with some sugar solutions and I found out that my brix scale is accurate, but the SG scale is off. So now I only use brix and convert to SG with the conversion when necessary. Here's where I talked about measure sugar solutions with it.

Thanks for that link. I missed that one, fell behind on required reading.

 

[ajdelange]

I'm guessing there is no way to correct them.. as there is no way to calibrate a hydrometer. Just have to know how far off you are and compensate?

You can calibrate/correct both!

Lets take the hydrometer first. Suppose you drop it, not hard enough to break it but hard enough that the paper on which the scale is printed slips 1/4" inside the tube. If you were to read distilled water at the temperature specified for the hydrometer and it were in perfect calibration before the accident the meniscus for water would be 1/4" one one side or the other of the 1.000 mark on the hydrometer. Noting this you would correct further readings by reading the scale 1/4" away from where the meniscus lies.

With a refractometer the same principle applies. If it reads off in distilled water you note by how much it is off and and add that correction to all readings. This gets a little dicey as the Brix scale isn't linear with refractive index (quite). The problem is the same with a hydrometer but with a hydrometer you have the option of measuring the offset in inches and correcting in inches (how much the paper slipped). With the refractometer you have to use its internal scale (Brix). You can do the same with the hydrometer. Electronic refractometers have no problem with this. You put a drop of DI water on the prism and press Cal. If the device is one you look through and has an adjusting screw then turning that rotates the scale so that the 0 Bx mark lines up with the boundary when DI water is on the prism. As accurate as refractometers are with respect to specific gravity the non linearity effect will not be significant.