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Conflicting Readings

Hello Everyone,

In preparing to bottle an English Barley Wine I brewed back at the first of the year, I decided to go back and check my refractometer’s FG reading against my hydrometer. Looking back at my notes, I saw that my refractometer gave an OG reading of 24* P or 1.101, and a FG reading of 12.2* P or 1.016. Today’s refractometer reading showed 12.2* P once again while the hydrometer read 1.018.

I felt pretty good about both of these readings being basically in the same ballpark, but got a little concerned when I ran the numbers through NB’s calculator (bottom of the page)

that estimates ABV & OG based on FG in Brix and SG. According to that calculator, the OG should have been 1.093 and not 1.101. This left me with two questions:

  1. Which number should I believe, my refractometer’s reading or the calculator’s estimate? I do check regularly to make sure that the refractometer is properly calibrated, so I don’t think there were any issues related to poor maintenance.

  2. Do refractometer OG readings become less reliable at higher gravities? The reason I ask is that I also had a suspicious refractometer reading a while back when measuring the OG of a Cabernet I was making. In that case, the refractometer gave a reading that was suspiciously low. In general, the calculator’s estimate has always agreed with my refractometer’s OG reading when brewing beers in the 1.048-1.060 range.

Any insight would be appreciated!

In the presence of alcohol refractometer readings will get you in the ball park, but are not as accurate as a hydrometer.

Run the numbers through other calculators and see if the results are the same.

A refractometer and a hydrometer will read approximately the same before fermentation begins; no correction required. Alcohol changes the refractive index of the solution, so once the yeast begins to produce alcohol, you need to correct your reading.

Calibrate both the hydrometer and the refractometer, and when in doubt, trust the hydrometer.

Thanks for the replies – I think my best bet may be to start using both instruments for OG & FG while using the refractometer for quick reference readings during brew day.

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