Quantcast

Hydrometer and refractometer discrepancy

HomeBrewTalk.com - Beer, Wine, Mead, & Cider Brewing Discussion Community.

Help Support Homebrew Talk:

kXb

Well-Known Member
Lifetime Supporter
Joined
Mar 21, 2013
Messages
61
Reaction score
2
Location
Austin
I was excited to try my new refractometer, Hanna Instruments Hi96811, to measure my Oatmeal Stout. I calibrated with distilled water and then checked reading again and got a reading of 0.0. I then checked my stout and got a brix of 8.0. This device has auto temp control and when converted to SG, that's 1.032.

I then checked my stout with my hydrometer. Temperature adjusted SG was 1.017. I checked my hydrometer with distilled water and it adjusts to .997 so not quite 1.00 as it should be but not a huge discrepancy.

What am I doing wrong?? I would not expect a difference of 1.032 to 1.017! And yes, I know how to read a hydrometer.

Thanks in advance
 

acidrain

Well-Known Member
Joined
Jul 31, 2012
Messages
2,198
Reaction score
225
Location
Seattle
Temperature adjusted? What exactly does that mean?
Hydrometers are only accurate withing a very narrow range.
What temperature did you sample?
 

flars

Well-Known Member
Joined
May 21, 2011
Messages
8,628
Reaction score
2,046
Location
Medford, Wisconsin
Refractometers are not accurate in the presence of alcohol. There are some conversion tools available, but the hydrometer will give you accurate readings once fermentation has begun.
 
Joined
Apr 23, 2009
Messages
34,020
Reaction score
12,993
Location
☀️ Clearwater, FL ☀️
Refractometers are not accurate in the presence of alcohol. There are some conversion tools available, but the hydrometer will give you accurate readings once fermentation has begun.
Yep, they don't work in the presence of alcohol.

I used the different calculators, including Sean Terrill's excellent effort. I never got my refractometer to work well with beer once alcohol was in the solution.

The problem is that there is a fudge factor, the "Wort Correction Factor (WCF)" that you need to empirically determine. Once you figure out what that is, the refractometer will be accurate ONLY WHEN YOU MEASURE THAT SAME BEER. If you brew a different beer, different color, different grist bill, the refractometer will not be accurate again until you determine the WCF for the new beer.

Use the refractometer during the boil and for the OG, but after that unfortunately it's back to the bobber.
 
OP
kXb

kXb

Well-Known Member
Lifetime Supporter
Joined
Mar 21, 2013
Messages
61
Reaction score
2
Location
Austin
Temperature was 75F and my hydrometer is calibrated to 60F.

Well poop, I didn't realize it was not useful after the boil and OG but I'm not too terribly disappointed. I haven't been testing during the boil but would like to. What is the process (other than the obvious usage of equipment) for testing during the boil (timeframe, relationship to OG, etc)??

Thanks
 

broadbill

Well-Known Member
Joined
Aug 30, 2007
Messages
3,955
Reaction score
561
Location
Southern Maine
Temperature was 75F and my hydrometer is calibrated to 60F.

Well poop, I didn't realize it was not useful after the boil and OG but I'm not too terribly disappointed. I haven't been testing during the boil but would like to. What is the process (other than the obvious usage of equipment) for testing during the boil (timeframe, relationship to OG, etc)??

Thanks
Its still fine to use post-boil to measure OG. It is the alcohol from yeast fermentation that throws it off. So anytime after yeast pitch it is a no-go without the correction tables.

Process for using during boil? What do you mean? You can test at any point during the boil, and the reading will be units of Brix, which you can then convert to specific gravity.
 

dmcman73

Well-Known Member
Joined
Apr 28, 2013
Messages
936
Reaction score
183
If you have an android phone/tablet, use an app called Brewzor calculator: https://play.google.com/store/apps/details?id=com.brewzor.calculator&hl=en

It has an excellent calculator for refractometers. Initially, take a reading with your hydrometer and record that value. Next take a reading with your refractometer and record that. Go into the app and select "Refractometer" from the menu. From the drop down menu at the very top (right under the words Input) select Calibrate. Enter your values into the approriate boxes and tap Save correction factor to preferences and the calculator will change the Correction factor and use that to calculate from. You'll find that your readings and calculations will be spot on after you calibrate your refractometer to your Hydrometer. Just make sure you select from the drop down menu the right measurement such as Unfermented wort (before pitching), Fermenting wort and finished beer to calculate the correct measurements.
 

Qhrumphf

Stay Rude, Stay Rebel, Stay SHARP
Lifetime Supporter
Joined
Apr 2, 2011
Messages
15,877
Reaction score
5,157
Location
Arlington (DC)
Temperature was 75F and my hydrometer is calibrated to 60F.

Well poop, I didn't realize it was not useful after the boil and OG but I'm not too terribly disappointed. I haven't been testing during the boil but would like to. What is the process (other than the obvious usage of equipment) for testing during the boil (timeframe, relationship to OG, etc)??

Thanks
Not sure what your brewing set up is, but assuming all grain brewing, a few things worth measuring (especially when a refractometer only requires a couple drops):

-First runnings gravity. Quick comparison to where it should be (Braukaiser has a chart of water to grist ratio and optimum first runnings gravity) can tell you when something's wrong.

-Various sparge gravities, particularly when fly sparging and to a lesser extent when doing multiple batch sparges, to make sure you're not oversparging. Sparge runnings with gravity below 1.010 are in danger zone for tannin extraction.

-The big one is preboil gravity. Stir the full preboil wort very very well or else you'll get a bad reading, and then the preboil gravity (expressed as gravity points, 1.056 would be 56) multiplied by the preboil volume will equal the postboil gravity (again as gravity points) by post boil volume. In other words 6.5 gallons of 1.056 wort boiled down to 5.5 gallons, 56*6.5=5.5*gravity=66.2, or 1.066 post boil gravity (your OG). If your preboil is low or high you can then adjust the gravity, volume, or boil time to hit the exact gravity that you want.

You can also continue monitoring the gravity throughout the boil as a second check. Although when it comes to volume measurment, at boiling you do need to keep thermal expansion of the wort in mind (and to a lesser extent with preboil if you're reading it in the mash/sparge range). Same math applies. You can also use the same math if you boil off too much and end up under volume/high on gravity to determine exactly where to top off to (or use for extract brewing or otherwise with partial boils to know exactly where to top off to)
 

doug293cz

BIABer, Beer Math Nerd, ePanel Designer, Pilot
Staff member
Mod
Lifetime Supporter
Joined
May 14, 2014
Messages
10,598
Reaction score
6,686
Location
Renton
You can also use it to tell when fermentation is complete, even though the reading may not be completely accurate (even after correction.) Just take samples two to three days apart, and when you get two successive identical readings, fermentation is done. If you want to be sure about the "real" final gravity, then take a hydro reading while racking to your bottling bucket or keg (just don't take the sample out of the bottling bucket with the priming sugar added.) I monitor my fermentation this way because it's easier to take the small sample needed by the refract, and I'm not losing a bunch of relatively large samples from my finished volume.

Brew on :mug:
 

poptarts

Well-Known Member
Joined
Mar 29, 2013
Messages
2,023
Reaction score
473
Location
Charlotte
You can also use it to tell when fermentation is complete, even though the reading may not be completely accurate (even after correction.) Just take samples two to three days apart, and when you get two successive identical readings, fermentation is done. If you want to be sure about the "real" final gravity, then take a hydro reading while racking to your bottling bucket or keg (just don't take the sample out of the bottling bucket with the priming sugar added.) I monitor my fermentation this way because it's easier to take the small sample needed by the refract, and I'm not losing a bunch of relatively large samples from my finished volume.

Brew on :mug:
What I do too, I find the calculators to be pretty accurate too, with in 1 point and honestly that 1 point might be me sucking at reading my hydrometer.
 
OP
kXb

kXb

Well-Known Member
Lifetime Supporter
Joined
Mar 21, 2013
Messages
61
Reaction score
2
Location
Austin
Not sure what your brewing set up is, but assuming all grain brewing, a few things worth measuring (especially when a refractometer only requires a couple drops)

I usually do a partial mash. Very good info...thanks to all for the input
 
Top