Author Topic: Refractometer WAY off...  (Read 2264 times)

Offline liquidbrewing

  • Brewer
  • ****
  • Posts: 283
  • OG - FG x 131= ABV%
    • View Profile
Refractometer WAY off...
« on: May 13, 2012, 09:06:44 AM »
So, somehow, both my hydrometers are broken.  Kegged a couple different batches yesterday, thought I'd pull out the refractometer.

Calibrated it with distilled water, read 0 brix.  Put a few drops of my new beer in there.  8.5 Plato?  Really, that's roughly 1.034 FG, after five weeks in the primary.

I have noticed a few threads on HBT that other people have had the same problem.  I've had the refractometer for a couple years, so returning it is out of the question.  Is it useless?  Should I toss it?

I borrowed a friends hydrometer and sampled the same beer, it finished at 1.010.  Right where I expected it.

This is the refractometer I have: http://www.rebelbrewer.com/shoppingcart/products/Economy-Refractometer.html
Justin
Liquid Brewing, Co.
"Find Your Own Level"

Offline Mark G

  • Brewmaster
  • *****
  • Posts: 898
  • Huntley, IL
    • View Profile
Re: Refractometer WAY off...
« Reply #1 on: May 13, 2012, 09:28:54 AM »
You have to correct for the alcohol in the finished beer. Try this...
http://seanterrill.com/2012/01/06/refractometer-calculator/
Mark Gres

Offline majorvices

  • Global Moderator
  • I must live here
  • *****
  • Posts: 7892
  • Polka. If its too loud you're too young.
    • View Profile
    • Yellowhammer Brewing Company
Re: Refractometer WAY off...
« Reply #2 on: May 13, 2012, 09:32:16 AM »
And even the corrected reading can be off. I only use my refractometer pre-fermentation. Never have been able to get an accurate reading post fermentation.
Keith Y.

Vote Jonathan Fuller for Governing Committee!

Offline tschmidlin

  • I must live here
  • **********
  • Posts: 8195
  • Redmond, WA
    • View Profile
Re: Refractometer WAY off...
« Reply #3 on: May 13, 2012, 11:12:31 AM »
I agree with both of the above - you need to correct and Sean's spreadsheet is the best I've tried.  But I still use my hydrometer post fermentation, no (potentially inaccurate) correction needed.
Tom Schmidlin

Offline jmcamerlengo

  • Brewmaster
  • *****
  • Posts: 625
    • View Profile
Re: Refractometer WAY off...
« Reply #4 on: May 14, 2012, 08:39:31 AM »
Out of curiousity which number from Sean's calculator do you guys use. I see New Cubic, new Linear etc.
Jason
-Head Brewer, Brewtus Brewers in the Shenango Valley. Hopefully opening a brewpub/nano brewery in the next couple years.

Offline hokerer

  • I spend way too much time on the AHA forum
  • ********
  • Posts: 2639
  • Manassas, VA
    • View Profile
Re: Refractometer WAY off...
« Reply #5 on: May 14, 2012, 10:59:02 AM »
Out of curiousity which number from Sean's calculator do you guys use. I see New Cubic, new Linear etc.

Sounds like you're looking at the spreadsheet.  Just use the online calculator instead..

http://seanterrill.com/2012/01/06/refractometer-calculator/
Joe

Offline jmcamerlengo

  • Brewmaster
  • *****
  • Posts: 625
    • View Profile
Re: Refractometer WAY off...
« Reply #6 on: May 14, 2012, 12:02:54 PM »
excellent, thanks Joe
Jason
-Head Brewer, Brewtus Brewers in the Shenango Valley. Hopefully opening a brewpub/nano brewery in the next couple years.

Offline dbeechum

  • Administrator
  • Brewmaster General
  • *****
  • Posts: 2417
  • Pasadena, CA
    • View Profile
    • Experimental Brewing
Re: Refractometer WAY off...
« Reply #7 on: May 14, 2012, 01:12:01 PM »
And even the corrected reading can be off.

Man, I feel like I must be smiled upon.. I do this all the time and everytime I've checked if I'm off it's my a point or two.. which is close enough for my needs.
Drew Beechum - Maltosefalcons.com
- Vote in the AHA GC Election! - http://bit.ly/1aV9GVd  -
-----
Burbling:
Gnome is in the Details
*Experimental Brewing - The Book*
Tap:
Peanut Butter Jelly Time
Tupelo Mead
Farmhouse Brett Saison

Offline bo

  • Senior Brewmaster
  • ******
  • Posts: 1141
    • View Profile
Re: Refractometer WAY off...
« Reply #8 on: May 14, 2012, 01:22:43 PM »
My refractometer is always within a point of my hydrometer. They're the greatest things since sliced bread.

Offline davidgzach

  • Senior Brewmaster
  • ******
  • Posts: 1659
    • View Profile
Re: Refractometer WAY off...
« Reply #9 on: May 15, 2012, 05:09:01 AM »
I have the same issue with mine.  The OG is spot on and the FG is not even close.  I'll try this spreadsheet.  Thanks for posting as it was driving me crazy!

Dave
Dave Zach

Offline Slowbrew

  • Senior Brewmaster
  • ******
  • Posts: 1994
  • The Slowly Losing IT Brewery in Urbandale, IA
    • View Profile
Re: Refractometer WAY off...
« Reply #10 on: May 15, 2012, 08:20:09 AM »
This thread reminds me that I need to calibrate my refractometer one of these days.

I'm with Drew on this and can say that the refractometer is always off 1 point or less on my FG.

For those not using a conversion tool (spreadsheet or online) you cannot expect the direct reading to be accurate in any way.  As was said earlier, the alcohol in solution changes the refraction.

Paul
Where the heck are we going?  And what's with this hand basket?