Gravity Help

[Yeastieboy]

I'm totally struggling with my gravity readings. I have both a refractometer and hydrometer. For my current brew, the OG was 1.052 (12.58 brix) as read from the refractometer. Following fermentation, it now reads 6.5 brix. When I plug these numbers into a calculator, it says the current gravity is 1.009. How come when I use my hydrometer, I'm seeing 1.025?? I must not be understanding something here! Help please.

 

[brewmeister13]

Hmmm...most people have the opposite problem, the refractometer reads much higher than the hydrometer. That is because refractometer readings are distorted by the presence of alcohol. I wish I could be more help with your problem though.

 

[Yeastieboy]

Either I am not understanding something here or one of my devices is wrong. Perhaps it's time to grab a gallon of distilled water.

 

[ncbrewer]

Read Brewmeister13's post again. They're not supposed to read the same after fermentation has started. But as he said, you should have the reverse problem - refractometer reading higher than the hydrometer. Once you calibrate on water, you should be able to figure the hydrometer is right.

 

[brewmeister13]

I just realized something after looking a bit closer at your original post. 6.5 brix isn't 1.009, it's closer to 1.026. You can use this calculator here to check: http://www.brewersfriend.com/brix-converter/

As far as the rest of what I was saying, refractometers aren't good for checking gravity after fermentation has begun. Here is a thread talking about it: https://www.homebrewtalk.com/showthread.php?t=333712

 

[Yeastieboy]

I was aware that the refractometer readings need correction during and after fermentation. What I was trying to explain in the original post is that when I plug my OG of 1.052 (~12.85 brix) into NB's calculator and my current reading of 6.50 brix, it's spitting out 1.009 as the current gravity. Time to test the hydrometer in some distilled water because it's reading 1.025. Tasting these samples, I feel it's much closer to 1.009 that 1.025!

 

[55x11]

I was aware that the refractometer readings need correction during and after fermentation. What I was trying to explain in the original post is that when I plug my OG of 1.052 (~12.85 brix) into NB's calculator and my current reading of 6.50 brix, it's spitting out 1.009 as the current gravity. Time to test the hydrometer in some distilled water because it's reading 1.025. Tasting these samples, I feel it's much closer to 1.009 that 1.025!

Just test with tap water. Should be very close to 1.000 in both refractometer and use hydrometer.

 

[Yeastieboy]

So I tested both devices with tap water and they are reading correctly. I'm still baffled.

 

[Gnomebrewer]

Do you have CO2 bubbles pushing your hydrometer up in the beer?
I find it difficult to measure lager FG's with a hydrometer for this reason.

 

[Yeastieboy]

That's certainly something to look in to. This is a fruit ale and I did notice more CO2 in the beer than usual at this point.

 

[ncbrewer]

I pour the FG sample back and forth between two glasses 20 times to de-gas it. It releases lots of foam. But I've checked the before and after a few times and only got 1 - 3 points difference. Still, I think it's good practice.

 

[Yeastieboy]

I will certainly try degassing a sample and retesting with the hydrometer. Doesn't sound like it would account for a difference of 0.016 though.

 

[Yeastieboy]

I degassed a sample this evening and the difference in hydrometer readings was negligible. Ugh...

 

[Gnomebrewer]

Try dissolving 8oz of sugar in a little water, then add water to make it up to a quart. This should have a gravity of 1.092. Check both your hydrometer and refractometer.

 

[ncbrewer]

Is it possible your hydrometer was resting on bottom when you got the weird reading?

 

[Yeastieboy]

Is it possible your hydrometer was resting on bottom when you got the weird reading?

No. I always ensure adequate liquid to sustain a buoyant hydrometer.

 

[Yooper]

Don't use NB's calculator.

Use this one: http://seanterrill.com/2012/01/06/refractometer-calculator/

While it's never been 100% accurate for me, it's the closest one I've found.

See what that one tells you.

I'm betting that your FG IS 1.025 since hydrometers are usually accurate unless the paper slips down or something- and then ALL the readings are off (including water).

 

[Yooper]

A good explanation is also on that website:

(answering a question why the brix scale doesn't directly 'translate' to FG)

3°Bx is 1.012 SG, but refractometers don’t measure gravity. They measure the refractive index. Before fermentation, the two are directly related, but once there’s alcohol in solution they aren’t. Hence the need for an FG calculator.

http://seanterrill.com/2010/06/11/refractometer-estimates-of-final-gravity/

 

[Yeastieboy]

A good explanation is also on that website:



(answering a question why the brix scale doesn't directly 'translate' to FG)



3°Bx is 1.012 SG, but refractometers don’t measure gravity. They measure the refractive index. Before fermentation, the two are directly related, but once there’s alcohol in solution they aren’t. Hence the need for an FG calculator.



http://seanterrill.com/2010/06/11/refractometer-estimates-of-final-gravity/

Thank you very much for the input and link. This calculator measures several points higher than NB's. Once again though, I am missing why measured brix pre-fermentation and measured brix post fermentation, with the correction factors applied, would be so out of whack with the hydrometer. All equipment is calibrated. I can't imagine everyone using a refractometer is experiencing a calculated FG of roughly 0.013 - 0.016 higher than a hydrometer. Seems like that would render the refractometer worthless, for beer anyways.

 

[DurtyChemist]

I'm in a similar boat as you but the opposite. MY hydrometer is reading LOW. I brewed 1.069 wort and the refractometer came in at 1.062. Even after reading everything I could saying refractometers are for sugar and wort isn't 100% sugar it didn't make sense. Everything said the refractometer should read HIGHER and mine wasn't. I found a hydrometer correction spreadsheet I'll be using to find a correction factor for my refractometer and I'd suggest the same. If you pm me your email I'll send you what I found and you can see if you like it.

I do suggest making a measured solution such as 4oz sugar into 1 pint of water and measuring it with both the refractometer and hydrometer to see if there is something funny going on.



For my refractometer I calibrate it with tap water because I didn't want to go buy distilled. It measures 0.000 for my hydrometer so I figured I'd be fine but for the price I'll just buy some distilled and see if it makes a difference. After that I'll do as I suggested and make a sugar/water solution to measure against the calibration and aim for something around 1.060-1.080 and log that into my spreadsheet in case things get funny in the future as well. Otherwise I'll be putting this up for sale and let someone else deal with calibrating the thing.

 

[Yooper]

Thank you very much for the input and link. This calculator measures several points higher than NB's. Once again though, I am missing why measured brix pre-fermentation and measured brix post fermentation, with the correction factors applied, would be so out of whack with the hydrometer. All equipment is calibrated. I can't imagine everyone using a refractometer is experiencing a calculated FG of roughly 0.013 - 0.016 higher than a hydrometer. Seems like that would render the refractometer worthless, for beer anyways.

Well, in many cases people don't really care all that much what the FG is- as long is the beer IS at FG. For me, I use a refractometer on brewday to check preboil readings, readings at the end of the sparge, etc, and then use a hydrometer after that.

Both tools have their place in my brewing arsenal, and can't replace each other. Think of it this way- a hammer is awesome and useful (refractometer). But if you need a screwdriver (hydrometer), a hammer just won't do the job.

 

[kh54s10]

The easiest thing is to measure the OG of a wort with the refractometer and the hydrometer. They should agree. If not you need to find out which one is off.

Then pre-fermentation use the refractometer...
And post fermentation use the hydrometer...

I sometimes use the refractometer post boil but only to see if fermentation is done. That the number stays the same over a period of 24 - 48 hours.

 

[Yeastieboy]

Old thread but I ran into the same issue again, this time with a lager. @Gnomebrewer mentioned earlier about having issues related to CO2, specifically with lagers. Therefore, I tried degassing a sample again and this time there was tons of CO2 in suspension after 3 weeks in the primary. This sample went from 1.018 to 1.011-12 after degassing. Amazing. I'm really happy this one completed and will be moving it to the keg tomorrow for lagering.