First Time Refractometer User Can't Figure it Out.

[GrowleyMonster]

Something funny going on here. I just put a batch in the keg a couple days ago without taking SG. I bought this refractometer a couple months ago and rather than pull a big ol test sample, I thought ah-HAH! That gadget only needs a couple of drops to test specific gravity! It's about time I tried it!
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So I read the instructions, and calibrated it. Then I popped a faucet on the beer out post of the keg, pulled a couple of ounces (hey, I wanted to taste it, too.) and sucked up a tiny bit in the supplied pipette thingy. Dropped it on the prism and flipped the cover thingie down on it, aimed at the window for light, and got a reading of 1.034. This is for an ale that saw two weeks of primary and over two weeks in secondary. I expected to see something in the neighborhood of 1.012, right? My og was 1.074 as I recall. No way that was right! I took a sg on a similar batch I have in primary almost ready to rack to the secondary BMB, and it should have been within a couple points of final. It tested about the same! Then I looked for and found a can of Abita Amber that somebody had left in one of the fridges here at the House of Growl, and tested it. 1.019! No way that stuff is over 1.01 in the can!!!

So back to the batch in the keg. When I tested it the other scale, the Brix scale, was at like 8.7%. What is that telling me? That beer should be around 8.14% ABV and I know Brix is not ABV, but is relate I am a little bit confused here. What am I doing wrong? Is this thing defective, or just messing with my head?

 

[Spartan1979]

A refractometer needs an algorithm to correct the reading once alcohol is present in the beer. One is here: https://www.brewersfriend.com/refractometer-calculator/ I haven't tried this one, there are others out there. Even with the algorithm it's not all that accurate but it will give you and idea where you are and if fermentation is present.

This calculator would indicate that you are around 1.011, about where you expected.

 

[Velnerj]

When testing solution with alcohol present your refractometer is going to be off. But there's a formula that can correct it. There are plenty of these calculators on the world Wide webs, I use Sean Terrill's.

You'll need the original brix reading plus the current brix to get the actual finished corrected reading.

Good luck.

 

[dmtaylor]

A refractometer needs an algorithm to correct the reading once alcohol is present in the beer. One is here: https://www.brewersfriend.com/refractometer-calculator/

I'm a proponent of the BrewersFriend calculator (which actually uses the Petr Novotny equation) and I find it to be VERY accurate when compared with a hydrometer within 0.001 on average, at least after your personal correction factor is determined (mine is 0.99). I don't even use a hydrometer half the time anymore it is so accurate. Terrill's equation is more accurate for lower FG beers below about 1.013, whereas the BF calculator is more accurate >1.013.

But yes, absolutely, thou shalt calibrate with water frequently -- if it ain't reading 0 in water, it either needs calibration or it's broken -- and thou shalt use a conversion calculator like this one.

 

[Robert65]

+1 for the Petr Novotný equation. I find it extremely accurate at all gravities. Within 0.001 sp. gr., as Dave said. But you do need to have an initial value, since the relationships between density, sugar, and alcohol are not linear but depend on the starting gravity; so if you didn't establish that, it's too late for this batch.

Refractometers can be excellent tools for brewing. I have a digital refractometer made for brewing, which requires no initial correction, as it is calibrated to maltose solutions rather than sucrose. Using the Novotný equation in my spreadsheet, I have no real need for a hydrometer at any stage of the process from dough in to finish. If your refractometer is a standard, hand held, Brix unit intended for winemaking (what is usually sold to homebrewers,) the initial correction factor should be ~1.04, which accounts for for the difference in refractive index between the sucrose it is calibrated to and he maltose that is predominant in wort. I believe if there appears to be an "instrument specific" correction significantly different from this, it indicates a faulty instrument. Or perhaps a faulty eyeball, idk.

 

[GrowleyMonster]

Wow cool. Lots good answers so I'm just gonna like everyone! Anyway so if the calculated FG is 1.011 then I am good as gold. .063 * 131.25 = 8.27% ABV. I can live with that. Meanwhile I bet I don't forget to take a hydrometer reading again!

'IwlIj jachjaj! (just trying to slip a few Klingon words into my everyday speech)

 

[passedpawn]

'IwlIj jachjaj! (just trying to slip a few Klingon words into my everyday speech)

Haha. Nice. I think you have a future here.

 

[Robert65]

Haha. Nice. I think you have a future here.

Indeed!

Qapla'!