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Refractometer question

Northern Brewer General
#1

Hi. Ok, this may be a ‘greenhorn’ question. I bought a refractometer (with automatic temp conversion) through NB a couple months ago, and I’ve been trying to learn how to use it. Every site I seem to come across, though, talks about converting Brix to SG. The device I bought, though, has a Brix scale on the left side (when peering through the eyepiece) and a SG scale on the right. Even with that, though, the NB site says I will need to do some calculations for final gravity.

Could someone tell me if I’m able to simply take the SG reading during fermentation and trust it, because I don’t at the moment, easy as it is.

For example, I just brewed a Dead Ringer pale ale extract. The OG came out at 1.071, per the refractometer. After almost 3 weeks in primary, I transferred to secondary and took a reading, and it was 1.034. Both readings seem high to me. Unfortunately, I didn’t think at either time to take a reading with a standard hydrometer (just a bit rushed for time and forgot).

I’m sure the question has been asked before and the answer is out there somewhere, but as I said, everywhere I’ve looked talks of conversion from Brix to SG, but I’m not sure if I have to with this device or not.

Thanks for any insight.

#2

It’s possible that the refractometer is out of adjustment. Checking it with RO/DI water will get you real close. But there is also a test fluid you can purchase. Check with a local pest store to see if they carry some. ( salt water fish tanks)

After fermentation starts, the alcohol skews the reading. If you have one of the big brewing software programs, there are calculators in them to adjust the reading. Or this site has one.

http://www.brewheads.com/refract-currentgrav.php

It would be good to take a reading with the hydrometer for a while and see if you are getting the same numbers with the calculators.

#3

I find that the only way to use the refractometer during fermentation is to save beer when seeing when fermentation is done. I don’t get a good FG reading. The calculators always convert to a lower FG reading than the hydrometer reads… i.e. with my Maibock right now Brix is 7.8 (OG of 1.071) converted to 1.008 FG with BeerSmith. The refractometer reading is 1.016. Both instruments are calibrated (0 Brix, 1.000 with dH20). Thus, I’ll use the refractomer just to make sure the beer is stable at a certain BRIX. Then, I’ll take a hydrometer reading to get the FG. I want to taste the beer at that point anyway.

I was thinking that once you get to a certain %ABV that you can’t use those calculators anymore, but I have not tested that theory. It’s usually only off by 0.001-2 on my low %ABV house pale ale.

#4
http://www.onebeer.net/refractometer.shtml

Once alcohol is in the test sample, it throws off the refract-o measurement. So use the above link to calculate your refract-o readings.

That should solve your problems.

Your beer went from 17.1 brix(1.071) to 8.4 brix (1.010) brix…which MEANS, it’s now @ 1.010, 7.9% ABV.

#5

Divide the refractometer reading by 1.04 (the correction factor to account for the fact that wort is not 100% sucrose which is what a refractometer is calibrated to read). If you want the OG in specific gravity instead of Plato, take the corrected reading and plug it into this formula - 259/(259-X) where X is the reading.

#6

Ok, so no matter what, I need to make some calculations or use one of the calculators. If I am to read in Brix and use the calculator anyway, then why does the refractometer have the SG scale on the right side?

#7

I also just purchased the same unit. Based on the NB website, I’m going with the gravity scale on the right side is a correct representation of specific gravity pre-fermentation. Adjustments would have to be made once fermentation starts and alcohol is present.
Per NB website:
“Same as our Brix Refractometer with the addition of a specific gravity scale. You won’t have to do conversions between Brix and gravity when measuring musts or wort. Measuring final gravity accurately will still take some calculations.”
Make sure you calibrate it and test it. I calibrated using distilled water but on my first use measuring wort I had a .04 O.G. variance from refractometer (1.046), to hydrometer, (1.050). I’m going to try calibrating using wort and then calibrate to my hydrometer, then see what it reads using DW.

#8

So you can see what your OG is without looking at a hydrometer or a converter.
A lot of refractometers only read Brix, the people who made the program for doing FG must’ve had one of those.

#9

That makes sense, and it’s starting to come together in my head. Thanks for all the responses.

#10

Had I not just come from a beer festival, I’d type more.

Background on how a refractometer works and how to use it in brewing: http://seanterrill.com/2010/06/11/refra … l-gravity/
Results of some experiments on how to use a refractometer to estimate FG: http://seanterrill.com/2011/04/07/refra … g-results/
Quick, plugi-in-th-numbers calculator: http://seanterrill.com/2012/01/06/refra … alculator/

There is no other technique that will give reasonabe accuracy when using a refractometer to estimate FG. Period.

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