Author Topic: SG/Brix refractometer completely useless?  (Read 2477 times)

Offline phillamb168

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Re: SG/Brix refractometer completely useless?
« Reply #15 on: April 29, 2011, 01:54:53 AM »
I have a couple of apps for my iphone that both convert brix to sg with numbers the same as every conversion graph, spreadsheet i have seen.  simple enough at high og to add a point or two based on experience.  free apps by the way.

I use refractool - what do you use?
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Offline enso

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Re: SG/Brix refractometer completely useless?
« Reply #16 on: May 02, 2011, 11:37:06 AM »
Got it today.  Seems pretty solid.  Checked it with distilled and it was calibated.  Tried it with a sample of birch sap I had left.  Seemed to be on.  Have to retake a hydrometer reading and see.

Yes the S.G. is apparently off.

For folks with the Brix only models, are they easier to read?  Maybe I should return it and get the Brix only...  But only if it is signifigantly easier to read.  I kind of don't want to bother with the hassle/time.  In other words I want to play with my new toy now!
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Offline Kit B

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Re: SG/Brix refractometer completely useless?
« Reply #17 on: May 02, 2011, 02:00:11 PM »
What's his reasoning?

He absolutely will not agree that the temperature corrections for SG & Brix are in correlation with one another.
He claims that temperature adjustment cannot be done for both, at the same time.
No matter how I explain both mathematically & with real-world examples, he will not agree.
At this point, he's probably just trying to be funny...I dunno.
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Re: SG/Brix refractometer completely useless?
« Reply #18 on: May 03, 2011, 07:13:15 AM »
He claims that it's impossible to have an ATC refractometer measure both.
I totally disagree.

Your friend is right, although he probably doesn't know why. A refractometer can only *measure* the refractive index. ;)
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Offline Kit B

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Re: SG/Brix refractometer completely useless?
« Reply #19 on: May 04, 2011, 01:08:08 PM »
OK...So, from what you're saying...
The 2 scales represent measurements of completely different things & they should not be used on the same instruments.
When explained in that manner, it actually almost makes sense.
But, why are we ever trying to use a refractometer to measure gravity of any kind, when really it can't truly provide us with that data, based on the refraction of light?

Is Brix a unit of measurement that is based on refraction, or is it a unit of measurement that is based on density?
I was under the impression that it was to measure liquid density of sucrose solutions.

I can somewhat agree that (with beer/wort) the refraction vs. gravity probably cannot be measured in this manner.
But, I have a hard time believing that you can predict the density of sucrose in a solution using a refractometer, yet not be able to use that same instrument to extrapolate Specific Gravity, with as much accuracy.

I don't mean to start any arguments...I really want to learn & understand this.
« Last Edit: May 04, 2011, 01:57:36 PM by Kit B »
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Offline tschmidlin

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Re: SG/Brix refractometer completely useless?
« Reply #20 on: May 04, 2011, 02:04:40 PM »
OK...So, from what you're saying...
The 2 scales represent measurements of completely different things & they should not be used on the same instruments.
When explained in that manner, it actually almost makes sense.
But, why are we ever trying to use a refractometer to measure gravity of any kind, when really it can't truly provide us with that data, based on the refraction of light?

Is Brix a unit of measurement that is based on refraction, or is it a unit of measurement that is based on density?
I was under the impression that it was to measure liquid density of sucrose solutions.
Brix and SG are both density measurements used to determine how much sugar is in a solution.  You measure the density directly and assume it is all from sugar in solution.  The Brix scale was originally determined with a hydrometer, taking measurements of solutions with known sucrose concentration.  The scale is set by % sucrose, and while that's not exactly what we're measuring it is close enough.

Refractometers measure the refractive index of the solution.  Sucrose has a known refractive index, so if that is all that is in the solution then it is easy to convert to either Brix or SG.  We assume as above, and it's close enough.

To say you can't measure Brix and SG at the same time is the same as saying you can't measure feet and meters at the same time.  If you print them both on the same tape measure, no problem.

If the SG reading on some hydrometers is "useless" it is because it was done wrong, like a measuring tape where each foot is 13 inches long.
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Offline Kit B

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Re: SG/Brix refractometer completely useless?
« Reply #21 on: May 05, 2011, 08:52:44 AM »
To say you can't measure Brix and SG at the same time is the same as saying you can't measure feet and meters at the same time.  If you print them both on the same tape measure, no problem.

This was my original stance, as well.
Thanks, for confirming.
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Re: SG/Brix refractometer completely useless?
« Reply #22 on: May 05, 2011, 10:32:43 AM »
If the SG reading on some hydrometers is "useless" it is because it was done wrong, like a measuring tape where each foot is 13 inches long.

That's a great analogy to these refractometers, and I'm going to steal it the next time this comes up. ;)
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