Author Topic: Understanding Refractometers  (Read 7678 times)

Offline GoodisBeer

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Understanding Refractometers
« on: November 08, 2012, 04:24:42 PM »
I can't figure out what my continued problem is. Just checked gravity of force fermentation sample. OG 1.060 and FG 1.028. Despite yeast starter and carbon filter I have still missed my anticipated FG 1.016. When using my Refractometer ATC do I need to make corrections to the final measurement based on weather I'm reading wort, fermentation, and/or finished beer?

The following article helps..kind of...Does BS have refractometer corrections for measuring diff types of samples?
 http://www.byo.com/stories/projects-and-equipment/article/indices/29-equipment/1343-refractometers
 http://onebeer.net/refractometer.shtml
Think I'm starting to answer my own question. " Once alcohol is present in the liquid a mathmatical correction must be applied"
http://www.homebrewstuff.com/refractometer-how-to
Can't find refractometer video that this video refers to. https://www.youtube.com/watch?v=JjVrqoLPziQ&feature=youtube_gdata_player

« Last Edit: November 08, 2012, 06:02:05 PM by GoodisBeer »

Offline jomebrew

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Re: Understanding Refractometers
« Reply #1 on: November 09, 2012, 11:11:12 AM »
The refractometer is designed to be used on unfermented liquid.  Once alcohol is present, the refractometer does not show the straight specif gravity you are looking for.  As noted, you must apply the value against an algorithm to compute the actual specific gravity.

Your best bet is a using a hydrometer.  Only adjustment needed is for temperature (they are calibrated for 60F).  There are some narrow range "final gravity" that are more accurate for measuring post fermentation.  In general, the narrower the range, the more accurate it is.

Offline durrettd

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Re: Understanding Refractometers
« Reply #2 on: November 09, 2012, 11:38:03 AM »
BeerSmith will calculate the refractometer correction for you. You said your finished fermentation was 1.028, so I assume you got that by converting from a refractometer reading of 7.2, not by using a hydrometer.  If you're using a hydrometer, disregard all after.

To get the corrected gravity: Click on "Tools" on the right side of the BeerSmith window, then click on "Refractometer". Select "Fermenting Wort Gravity", the middle function. Enter your OG (1.060) and the refractometer reading for your fermented wort, which was apparently about 7.2. Beersmith calculates a corrected final gravity of 1.009. Sounds like the system is working.

Dan


Offline durrettd

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Re: Understanding Refractometers
« Reply #3 on: November 09, 2012, 11:44:17 AM »
Good Grief! The "Tools" selection is on the LEFT, not the right! I'm attaching a picture.

Offline tom_hampton

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Re: Understanding Refractometers
« Reply #4 on: November 09, 2012, 11:48:11 AM »
Note that Beersmith includes the "fermenting wort" algorithm that Jomebrew mentions in its refractometer tool.  It works as advertised.

The thing that I would note is that cloudy beer where the yeast are still in suspension difuses the light, and makes the dividing line between blue and white in the refract a blur.  It doesn't bother me too much.  I pick the visual center of the blurry area and use that as input into BS2 for my SG estimate.  I don't really care about my exact SG DURING fermentation...only that it is still trending downwards.  I'm just checking to make sure it doesn't get stuck, and to build up a knowlege-base for how long fermentation takes in my conditions. 

Even with the blur I'm not off by more than 1/2 Plato (2 pts).  Once terminal gravity is reached, enough of the yeast has flocculated out, that I can get a good clear line for my final samples.  the only exception to that might be a hefe, but I didn't get my refract until after I was done making those this summer.  We'll see next year. 

I've put my hydrometer away since getting the refract.  I took both measurements (SG and Plato) for the first two brews.  But, once I knew I could trust the refract during fermentation (and the BS2 fermenting wort compensation), I've put it away and haven't looked back. 

I take a 30ml sample from the racking port, and take a quick reading every day.  Too easy.  I still get enough for a good taste test, but its a lot less of a hassle.  it used to take about 5 minutes start to finish with the hydro.  Now its like 30 seconds.  not a big deal....but, the lower the barrier to measurement, the more likely I am to take the measurements. 

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Offline GoodisBeer

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Re: Understanding Refractometers
« Reply #5 on: November 09, 2012, 01:38:07 PM »
Hey all appreciate all the feed back. I should of read up more on the use of a refractometer before jumping in.  As Tom may know I've been dealing with what I thought was poor fermentation for some time, come to find out I was just using my tools incorrectly. I usually take the long difficult route.  Ah but FUN!

Offline tom_hampton

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Re: Understanding Refractometers
« Reply #6 on: November 09, 2012, 01:47:27 PM »
Hey all appreciate all the feed back. I should of read up more on the use of a refractometer before jumping in.  As Tom may know I've been dealing with what I thought was poor fermentation for some time, come to find out I was just using my tools incorrectly. I usually take the long difficult route.  Ah but FUN!

No bleepin way!!!!  LOL  Now that's funny.  So your 1.023 stuck ferment was a refractometer reading? 

Ah....hard lessons learned....are not oft forgotten. 

Glad it finally makes sense.
R.I.P.:Belgian Blonde
On Tap: Apfelwein, Kolsch(v2), Pumpkin Ale, Belgian Specialty 
Aging/Storing: Coffee Porter, Chocolate Porter, Flanders Red, English Barlywine
Fermenting: Maggie's Altbier
Next Up: PtE(1.1), Belgian Dubbel?

Working thru all BCS recipes

Offline GoodisBeer

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Re: Understanding Refractometers
« Reply #7 on: November 09, 2012, 01:50:49 PM »
Yep..now I know how to make a yeast starter and differentially diagnosis a stuck fermentation.

Offline GoodisBeer

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Re: Understanding Refractometers
« Reply #8 on: November 15, 2012, 02:12:12 PM »
Force fermentation test reads at 7 brix, FG 1.010 after correction. Exactly where it needs to be.

 

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