Hydrometer reading V refractometer reading

[Wildknight65]

Hi all

Strange one here and any advice would be great.

I’ve just finished fermenting a high abv ipa. SG 1064.

Four weeks in the fermenter and I have taken a reading with my refractometer. This reading was 1023

I was disappointed this was too high so double checked it with my hydrometer and this read 1011. There is quite a bit of difference here. I have checked the calibration on my refractometer and this is spot on. I’ve check the readings several times from several samples and both come out the same

Has anyone any ideas on why the readings would be so different. And which one would you go with?

 

[thehaze]

The FG should only be taken with a hydrometer. If you use a refractometer, you need to adjust the FG: https://www.northernbrewer.com/learn/resources/refractometer-calculator/

 

[dyqik]

Your hydrometer reading is the correct reading of final gravity.

Refractometers and hydrometers measure different things - refractive index and density. Both are affected by the presence of alcohol in solution, but in different ways.

Since we are all used to using hydrometers to measure final gravity (density) to determine how far fermentation has gone/how dry a beer is, the effect of alcohol on the final gravity is already taken into account (and it's also taken into account in the equation to turn FG into ABV). The usual conversion from refractive index read by a refractometer doesn't allow for the presence of alcohol, just sucrose/glucose/fructose (maltose is accounted for by the wort correction factor you use in the conversion).

To convert a refractometer reading in Brix to an FG, you need to know the OG as well, so you can account for the alcohol and remaining sugars together. There are a couple of equations for doing that - either Sean Terrill's calculator or a newer calculation by Petr Novotný.

Sean Terrill's Calculator
Discussion of new calculation

Both can work fine for determining OG and FG/ABV/Actual Attenuation provided you use the right conversions and not a simple SG scale built into the refractometer. Even for OG before alcohol is present, you need to calibrate your refractometer for wort.

 

[myndflyte]

As others have said, you need to correct for the alcohol content. The AHA had a nice write-up about it and if you prefer to use equations instead of online calculators, here are their equations:

FG = -0.002349(Bxi) + 0.006276(Bxf) + 1
ABW = 0.67062(Bxi) - 0.66091(Bxf)
ABV = (FG x ABW) / 0.791

Bxi = Brix of unfermented wort
Bxf = Final Brix measurement

 

[Wildknight65]

Your hydrometer reading is the correct reading of final gravity.

Refractometers and hydrometers measure different things - refractive index and density. Both are affected by the presence of alcohol in solution, but in different ways.

Since we are all used to using hydrometers to measure final gravity (density) to determine how far fermentation has gone/how dry a beer is, the effect of alcohol on the final gravity is already taken into account (and it's also taken into account in the equation to turn FG into ABV). The usual conversion from refractive index read by a refractometer doesn't allow for the presence of alcohol, just sucrose/glucose/fructose (maltose is accounted for by the wort correction factor you use in the conversion).

To convert a refractometer reading in Brix to an FG, you need to know the OG as well, so you can account for the alcohol and remaining sugars together. There are a couple of equations for doing that - either Sean Terrill's calculator or a newer calculation by Petr Novotný.

Sean Terrill's Calculator
Discussion of new calculation

Both can work fine for determining OG and FG/ABV/Actual Attenuation provided you use the right conversions and not a simple SG scale built into the refractometer. Even for OG before alcohol is present, you need to calibrate your refractometer for wort.

Okay thank you for this, but I'm still a little confussed and glad I've asked this question as i had been using the refractometer without doing any conversions, luckily it was only on this 1 beer, the rest were done using a hydrometer.

so my refractometer measured 13 brix as my OG, (i did not take a hydrometer reading) My final reading using the refractometer was 5 Brix. so using the calculator, if I'm understanding this correctly, my OG reading was 1.052, and my FG was 1. the calculator says 1, but my hydrometer reading was 1.010, giving a difference abv between 6.79% and 3.47%, am i confessing you now

 

[balrog]

13.0 to 5.0 on Brewers' Friend give OG 1.050, FG 1.007; if wort correction is default 1.040 (depends on your refractometer)

 

[fun4stuff]

Okay thank you for this, but I'm still a little confussed and glad I've asked this question as i had been using the refractometer without doing any conversions, luckily it was only on this 1 beer, the rest were done using a hydrometer.

so my refractometer measured 13 brix as my OG, (i did not take a hydrometer reading) My final reading using the refractometer was 5 Brix. so using the calculator, if I'm understanding this correctly, my OG reading was 1.052, and my FG was 1. the calculator says 1, but my hydrometer reading was 1.010, giving a difference abv between 6.79% and 3.47%, am i confessing you now

Just use brewersfriend calculators to convert brix to s.g.. (https://www.brewersfriend.com/refractometer-calculator/). You can further increase accuracy by determining your wort correction factor (https://www.brewersfriend.com/how-to...ection-factor/).

 

[Wildknight65]

cheers guys, i think I'm going to go back to my good old hydrometer, its more accurate it seems

 

[balrog]

cheers guys, i think I'm going to go back to my good old hydrometer, its more accurate it seems

that will always be a good idea, especially when alcohol is present --but check your hydrometer every so often as well -- the paper inside with the printed scale can actually move!