Refractometer reading very different from Hydrometer, fermenting wort

[beervoid]

Hi everyone, I've had a slow fermentation going due to pitching to low. I meassured the OG with an hydrometer as 1.081. Normally my fermentation is at terminal around day 4.
Now day 7 in it's still bubbling quiet alot so I decided to do a refractometer reading. It stated 11.5 brix which calculate to 1.024, to double check I also did a hydrometer reading and to my surprise it read 1.034 which is MUCH higher.
At first I thought perhaps cause there is still fermentation going on and I could see pieces float the reading is off. I decided to put the sample in the fridge to let it cool down, but when taking a hydrometer reading this time it was still around 1.032.

I did not take a refractometer brix reading for the OG. I calculated this to be 20.2brix calculating back from the OG of 1.081. Is this perhaps not a good way to do it?
Can fermenting wort skew a hydrometer somehow?
Any thoughts are welcome

 

[dmtaylor]

Refractometer conversion calculators are less accurate: (A) when your OG was high, and (B) when the wort is still fermenting.

Your hydrometer has the correct reading in this case. Don't use a refractometer for this batch.

 

[hotbeer]

IMO, in most every case the very simple glass hydrometer with the bulb on one end and a long thin neck with the scale in it is going to be the most accurate. And it's pretty quick to check the calibration of it to within 0.001 SG even if you just use tap water at the temp it comes out of the faucet instead of distilled water at 68°F or 60°F depending on the maker of your hydrometer.

I have however been surprised at how just a few tiny bubbles clinging to the hydrometer can sometimes significantly change it's reading. Usually giving the hydrometer a good spin will rid it of the bubbles.

 

[AlexKay]

This would be what I'd expect for a still-fermenting sample.

Good hydrometer measurements require better temperature control and sample de-carbonization than refractometer measurements do. It's possible your hydrometer reading is off because of this. The refractometer reading is more robust.

As for which measurement is "right" ... for ABV determination, neither one is. If you're trying to figure out how much your beer weighs, the hydrometer is right. If you're comparing to a previous batch, you want to use the same method to measure this time.

And yes, for measuring wort, it's perfectly reasonable to take a refractometer measurement you made by reading the SG scale and back-calculating Brix.

 

[beervoid]

IMO, in most every case the very simple glass hydrometer with the bulb on one end and a long thin neck with the scale in it is going to be the most accurate. And it's pretty quick to check the calibration of it to within 0.001 SG even if you just use tap water at the temp it comes out of the faucet instead of distilled water at 68°F or 60°F depending on the maker of your hydrometer.

I have however been surprised at how just a few tiny bubbles clinging to the hydrometer can sometimes significantly change it's reading. Usually giving the hydrometer a good spin will rid it of the bubbles.

I also thought I should keep with the hydrometer reading as most accurate but to see such a big difference of 8 points seems strange.
And I've always had close enough readings with the refractometer after using brewersfriend calculator and finding my right index.

I did the spin and I even cleared the wort sample down in the fridge to get rid of ferment trub and bubbles. It read 2 points lower.

This would be what I'd expect for a still-fermenting sample.

Good hydrometer measurements require better temperature control and sample de-carbonization than refractometer measurements do. It's possible your hydrometer reading is off because of this. The refractometer reading is more robust.

As for which measurement is "right" ... for ABV determination, neither one is. If you're trying to figure out how much your beer weighs, the hydrometer is right. If you're comparing to a previous batch, you want to use the same method to measure this time.

And yes, for measuring wort, it's perfectly reasonable to take a refractometer measurement you made by reading the SG scale and back-calculating Brix.

I use an online calculator to correct the FG, I've done this for quiet some time and even calibrated the wort adjustment factor.
The refractometer is always very close to the hydrometer.
As for fermenting wort, even putting it in the fridge for an hour to clear the sample and making sure no co2 is in there, the hydrometer is reading about 10 points higher.
This seems super high if you ask me?
If I go by the refractometer it seems my beer is nearly at terminal which was calculated.

Did a reading again today.
Hydrometer reads 1.030
Refractometer 10.6 (1.019)

 

[wallyLOZ]

I started with one gallon batches and a hydrometer. That took way too much beer out of the fermenter so I bought a refractometer. I used both for the next twelve batches and after using the calculator, never had more than 0.002 difference. I've since mothballed the hydrometer. YMMV

 

[beervoid]

I started with one gallon batches and a hydrometer. That took way too much beer out of the fermenter so I bought a refractometer. I used both for the next twelve batches and after using the calculator, never had more than 0.002 difference. I've since mothballed the hydrometer. YMMV

Have you ever taken a hydrometer sample DURING fermentation?
I'm very curious to see how this batch turns out when its all done and packaged.

 

[hotbeer]

I've had some batches early on that would bubble and stop, then bubble and stop multiple times. Sometimes the beer would almost be clean and transparent so I could see across the trub/yeast layer and then it would start bubbling again and everything would get churned up on the bottom. One did that for many weeks and I didn't bottle it till week 6 and another did the same and didn't get bottled till week 5.

Those were among what I considered some of the best beers I've made. And I didn't worry about what the SG was during the time they were in the FV. I figured that by the time they cleaned up and looked dead for 3 or 4 days, they were way passed having reached FG.

The measured SG at bottling time was within a point or two of the predicted FG.

So unless you are in a hurry, you might just wait this out and see what it becomes.

 

[wallyLOZ]

Have you ever taken a hydrometer sample DURING fermentation?
I'm very curious to see how this batch turns out when its all done and packaged.

No, I haven't. I generally leave the beer in the fermenter for three weeks, then bottle. Never thought of checking during fermentation. Always thought that the fewer times that I crack open the fermenter the better.
If you do, let us know the results.

 

[odie]

I think both are just fine. all that matters is the gravity difference from start to finish. Use one or the other. but the only thing you really care about is the change in gravity so you can calculate ABV

 

[beervoid]

Can a refractometer be off cause it was dropped or something else?
I have measured a finished pale ale which reads 1.012fg with a hydrometer but with the refractometer its at 1.002 (4.6brix) so that's waaay off. OG of this beer was 1.045 (11.3brix)

 

[beervoid]

Just checked the beer in question which is now cold crashed and dryhopped. Hydrometer gives me 1.026, refractometer (tried 2) both read 10.6brix which is 1.019-1.021 so also very much off

 

[dmtaylor]

You’re doing something wrong. I would have to look over your shoulder to figure out what you are doing wrong. Either that or your instruments are all busted.

 

[balrog]

Make yourself a sugar solution, by weight (sugar and water), and measure both instruments.

 

[camonick]

^^^this is the answer.
Use distilled water and a sugar solution at the correct temperature to check the calibration of each tool. There’s no other way to know and everything is just speculation until you verify their accuracy

 

[balrog]

Make yourself a sugar solution, by weight (sugar and water), and measure both instruments.

And because I always like having directions,

"to make 1.040 sucrose solution one dissolves 103.7 grams sucrose in 3/4 L of water and then makes up to 1 L"

From here.

 

[beervoid]

Good recommendations guys! I will make the sugar solution and report back.

 

[bobtheUKbrewer2]

beervoid, at end of fermentation they are both off, in opposite directions, make a sugar solution at 1.005, measure it with both instuments, then add 5% vodka, repeat both measurements - discuss....

 

[Birhanen]

Have you ever taken a hydrometer sample DURING fermentation?
I'm very curious to see how this batch turns out when its all done and packaged.

 

[Birhanen]

The refractory meter is exellent in following fermentation and producing the fermentation curve.

 

[jschein]

And because I always like having directions,

"to make 1.040 sucrose solution one dissolves 103.7 grams sucrose in 3/4 L of water and then makes up to 1 L"

From here.

Always like when someone refers to an older @ajdelange post.
What a wealth of knowledge