Author Topic: Refractometer errors?  (Read 2747 times)

Offline BrewQwest

  • Cellarman
  • **
  • Posts: 79
    • View Profile
Refractometer errors?
« on: February 19, 2010, 08:24:52 PM »
I thought I had this figured out but my last couple of batches are falling way short from my stated SG.  My last two batches were identically 0.6 too low in gravity as read with the refractometer.  For example, I read 12.6 Brix (approx 1.052) with my refractometer but the hydrometer reads 1.049 (approx 12Brix).  My starter read 1.032 (approx 8 Brix) with the hydrometer but reads 8.6 Brix (approx 1.035) with the refractometer.  Can't I just 're-calibrate' my refractometer by dialing in an 8 Brix reading when I read my starter which was at 8.6 Brix??  ???  please help, and thanks, cheers!!
On a never-ending journey for the perfect pint of beer...

Offline Thirsty_Monk

  • Brewmaster General
  • *******
  • Posts: 2222
  • Eau Claire WI
    • View Profile
Re: Refractometer errors?
« Reply #1 on: February 19, 2010, 09:40:42 PM »
I think you have issue with your conversion formula because 12.6 Brix is about 1048.
What formula are you using?
Na Zdravie

On Tap At The TapRoom:
Bohemian Pilsner
Bohemian Dark Lager
Smoked Bock
MaiBock
American Brown Ale
Marzen
Root beer

Offline BrewQwest

  • Cellarman
  • **
  • Posts: 79
    • View Profile
Re: Refractometer errors?
« Reply #2 on: February 20, 2010, 06:40:16 AM »
I think you have issue with your conversion formula because 12.6 Brix is about 1048.
What formula are you using?

Thirsty_Monk, that could be.  I tried using a chart on another forum but it was further off than the following formula. I searched the net until I found the following formula which I have been using:

SG = 1.000898 + 0.003859118*B + 0.00001370735*B*B + 0.00000003742517*B*B*B

where:
B = measured refractivity in Brix
SG = calculated specific gravity at 15 C  (59F)

any further help would be greatly appreciated.. thank you
On a never-ending journey for the perfect pint of beer...

Offline Thirsty_Monk

  • Brewmaster General
  • *******
  • Posts: 2222
  • Eau Claire WI
    • View Profile
Re: Refractometer errors?
« Reply #3 on: February 20, 2010, 09:41:36 AM »
I think there was just discussion on this forum about formula to convert brix to Plato and to original gravity.

I am not a big formula guy.
I use ProMash where I enter Brix and it will do conversion.
You could also check More Beer refract spread sheet that is pretty accurate.
http://morebeer.com/learn_vids/vids_refract

Are you writing your own program/spreadsheet?
Na Zdravie

On Tap At The TapRoom:
Bohemian Pilsner
Bohemian Dark Lager
Smoked Bock
MaiBock
American Brown Ale
Marzen
Root beer

Offline BrewQwest

  • Cellarman
  • **
  • Posts: 79
    • View Profile
Re: Refractometer errors?
« Reply #4 on: February 21, 2010, 10:44:04 AM »
Thirsty, I believe you are correct in that I am using the wrong conversion table.  After watching the morebeer video, it stated that 15 Brix = 1.060 gravity.  According to my chart, I show 15 Brix = 1.062 gravity, while the older chart showed 15 Brix = 1.063 gravity.  On my chart, 1.060 gravity = 14.5 which is darn well near the 6 Brix I am always off.  What formula or what chart is everyone else using??   :-\
On a never-ending journey for the perfect pint of beer...

Offline Thirsty_Monk

  • Brewmaster General
  • *******
  • Posts: 2222
  • Eau Claire WI
    • View Profile
Re: Refractometer errors?
« Reply #5 on: February 21, 2010, 06:35:40 PM »
Na Zdravie

On Tap At The TapRoom:
Bohemian Pilsner
Bohemian Dark Lager
Smoked Bock
MaiBock
American Brown Ale
Marzen
Root beer

Offline BrewQwest

  • Cellarman
  • **
  • Posts: 79
    • View Profile
Re: Refractometer errors?
« Reply #6 on: February 23, 2010, 08:23:54 AM »
Ok, on the morebeer site I downloaded the spreadsheet and the formula for the BRIX to SG conversion.  Unfortunately, it appears that whichever formula one uses, will determine how far off their conversions will be.  Taking the lower variables from my original formula and the newer formula (from morebeer spreadsheet) and applying them, morphs into yet another formula which further adjusts the conversions getting my readings closer to what my hydrometer is saying. Since I am no mathematician, I found myself wanting to further 'enhance' the formula so that my refractometer actually equates with my hydro reading.  Fortunately, I caught myself, and now am wondering why they just do not make a refractometer that reads gravity like a hydrometer.  Wouldn't that be the best of both worlds?  Is that even possible?   :)
On a never-ending journey for the perfect pint of beer...

Offline Kaiser

  • Global Moderator
  • Senior Brewmaster
  • *****
  • Posts: 1797
  • Imperial Brewing Geek
    • View Profile
    • braukaiser.com
Re: Refractometer errors?
« Reply #7 on: February 23, 2010, 08:33:12 AM »
Fortunately, I caught myself, and now am wondering why they just do not make a refractometer that reads gravity like a hydrometer.  Wouldn't that be the best of both worlds?  Is that even possible?   :)

Yes, that is possible but you have to keep in mind that the market for this refractometer is limited to brewers as it would only read the correct gravity for brewer’s wort. It may even be so limited that it only reads the correct gravity of all malt brewer’s wort. All it takes is a replacement of the scale mounted inside the refractometer.

Much less confusing would be a refractometer that reads the refractive index and you would use a table to convert it to the wort specific gravity. This is pretty much what you do now only that the refractive index is expressed as the sugar content (Brix) of a sugar solution that has the same refractive index as you sample.

Kai

Offline a10t2

  • Official Poobah of No Life.
  • *
  • Posts: 3833
  • Ask me why I don't like Chico!
    • View Profile
    • SeanTerrill.com
Re: Refractometer errors?
« Reply #8 on: February 25, 2010, 08:43:54 AM »
Is it possible you're simply forgetting to apply the wort correction factor?

12.6/1.04 = 12.1 -> 1.050
8.6/1.04 = 8.3 -> 1.034

The thread Thirsty_Monk linked to gets into this.
Sent from my Microsoft Bob

Beer is like porn. You can buy it, but it's more fun to make your own.
seanterrill.com/category/brewing | twomilebrewing.com

Offline toastedman

  • 1st Kit
  • *
  • Posts: 21
    • View Profile
Re: Refractometer errors?
« Reply #9 on: March 09, 2010, 06:26:51 PM »
wondering why they just do not make a refractometer that reads gravity like a hydrometer.  Wouldn't that be the best of both worlds?  Is that even possible?   :)

   
  there is a refractometer that reads gravity, I have one, it reads brix-scale on left side and gravity-scale on the right side. i just calibrate it to read same as my hydrometer, i can check my runnings at any time and see reading in gravity-scale.
 

Offline Kaiser

  • Global Moderator
  • Senior Brewmaster
  • *****
  • Posts: 1797
  • Imperial Brewing Geek
    • View Profile
    • braukaiser.com
Re: Refractometer errors?
« Reply #10 on: March 09, 2010, 08:39:56 PM »
  there is a refractometer that reads gravity, I have one, it reads brix-scale on left side and gravity-scale on the right side. i just calibrate it to read same as my hydrometer, i can check my runnings at any time and see reading in gravity-scale.

Even if it reads gravity it may not be the same gravity that you measure with a hydrometer if you use wort. Chances are that it reads the correct gravity of a sucrose solution.

Kai

Offline toastedman

  • 1st Kit
  • *
  • Posts: 21
    • View Profile
Re: Refractometer errors?
« Reply #11 on: March 09, 2010, 09:12:18 PM »
  there is a refractometer that reads gravity, I have one, it reads brix-scale on left side and gravity-scale on the right side. i just calibrate it to read same as my hydrometer, i can check my runnings at any time and see reading in gravity-scale.

Even if it reads gravity it may not be the same gravity that you measure with a hydrometer if you use wort. Chances are that it reads the correct gravity of a sucrose solution.

Kai

      The refactometer i have is for use for beer only, it measures gravity of wort, same as a hydrometer. its out in my backyard brewery, i'll tell you the details tomorro, its raining here now.

Offline toastedman

  • 1st Kit
  • *
  • Posts: 21
    • View Profile
Re: Refractometer errors?
« Reply #12 on: March 09, 2010, 09:53:36 PM »
  there is a refractometer that reads gravity, I have one, it reads brix-scale on left side and gravity-scale on the right side. i just calibrate it to read same as my hydrometer, i can check my runnings at any time and see reading in gravity-scale.

Even if it reads gravity it may not be the same gravity that you measure with a hydrometer if you use wort. Chances are that it reads the correct gravity of a sucrose solution.

Kai

      The refactometer i have is for use for beer only, it measures gravity of wort, same as a hydrometer. its out in my backyard brewery, i'll tell you the details tomorro, its raining here now.

   the same one i have is on e-bay,  the item # is (370317544138)

Offline BrewArk

  • Brewmaster
  • *****
  • Posts: 516
  • Rick - Newark, California
    • View Profile
    • BrewArk
Re: Refractometer errors?
« Reply #13 on: March 09, 2010, 10:26:48 PM »
That's sweet but for the upcharge, I'll use the spreadsheet and convert from Brix. :o
Beer...Now there's a temporary solution!

Na Zdraví