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General Category => Equipment and Software => Topic started by: enso on April 27, 2011, 08:02:45 PM

Title: SG/Brix refractometer completely useless?
Post by: enso on April 27, 2011, 08:02:45 PM
So I asked for one of these for my birthday only to now read in another thread that these do not work.  Are they completely useless or can I read the brix side of the scale and get an accurate reading?
Title: Re: SG/Brix refractometer completely useless?
Post by: glastctbrew on April 27, 2011, 08:19:56 PM
So I asked for one of these for my birthday only to now read in another thread that these do not work.  Are they completely useless or can I read the brix side of the scale and get an accurate reading?

I love my refractometer and couldn't imagine brewing with out it, I just completely ignore the SG scale.  I use Sean Terrill's spreadsheet to convert Brix to SG.  http://seanterrill.com/2011/04/07/refractometer-fg-results/  There is a spreadsheet link about 2/3rds of the way down page.
Title: Re: SG/Brix refractometer completely useless?
Post by: enso on April 27, 2011, 08:22:21 PM
So you have one that has SG and Brix then?  So long as the brix side works I will be glad.
Title: Re: SG/Brix refractometer completely useless?
Post by: tom on April 27, 2011, 08:25:14 PM
Once fermentation starts, the alcohol will mess with the reading.  You can just use a hydrometer or there are some correcting formulae you can plug into.  Check out Sean Terrill's site for more info on that.
Title: Re: SG/Brix refractometer completely useless?
Post by: enso on April 27, 2011, 08:28:46 PM
Yes I am aware of the alcohol issue.  I plan to only use it preboil and maybe during the boil.  What I am asking about is some folks have said the refractometers that have a dual S.G. and Brix scale do not work.  I was wondering if that meant it is completely useless or just the S.G. side is inaccurate.
Title: Re: SG/Brix refractometer completely useless?
Post by: glastctbrew on April 27, 2011, 08:41:14 PM
So you have one that has SG and Brix then?  So long as the brix side works I will be glad.

Yep, mine has Brix on left and SG on right side of the display.
Title: Re: SG/Brix refractometer completely useless?
Post by: Slowbrew on April 27, 2011, 09:30:25 PM
I have heard the SG scale is not very accurate but I cannot speak from experience.  My refractometer is Brix only and I love the ease of using it.

As for only using it for the pre-fermentation side of brewing I suggest you use it for readings during and after fermentation too.  I use a spreadsheet I downloaded from MoreBeer to do the conversion after there is alcohol in solution and it is dead on accurate.  You only need 2 values for it to do the calculation.  You need the reading (in Brix) of your OG and your current gravity ready (again in Brix) and it spits out you answer in Specific Gravity.

Paul
Title: Re: SG/Brix refractometer completely useless?
Post by: hopfenundmalz on April 27, 2011, 09:37:39 PM
Man, you shouldn't have told me it was useless!  All those beers over the last 5 years were crap then, and the awards were bogus.

Tell me what forum says this?

Seriously, you just have to understand the tool and use it properly.  Promash has both Brix and SG when you formulate the recipe.  You get used to looking at both and switching back and forth.  The morebeer converter is good for the FG.  I have been using a refractometer for so long, I would not go back to a hydrometer on the hot side.

Title: Re: SG/Brix refractometer completely useless?
Post by: a10t2 on April 27, 2011, 10:09:51 PM
I think I'm the one who started this...

With the caveat that I've never actually used one of these and and am working entirely from the pictures I've seen online, yes, the SG scale is inaccurate. The manufacturer appears to have used the "multiply by four" rule, rather than an actual Brix-to-SG conversion. So the Brix scale should be just as accurate as any other refractometer, but the SG scale will only be within one "point" up to about 1.050. As far as I know, the Brix scale is still a pure sucrose measurement, so you'll need to apply a correction factor when measuring wort.

This post has some general information on how to use a refractometer, as does the September 2, 2010 episode of Basic Brewing Radio: http://seanterrill.com/2010/06/11/refractometer-estimates-of-final-gravity/

For FG estimation, I have a recently updated spreadsheet, which glastctbrew linked to earlier: http://seanterrill.com/2011/04/07/refractometer-fg-results/

This *should* give better results than the MoreBeer/ProMash/BeerSmith/what have you formula, although that's also included so that people can verify it for themselves.
Title: Re: SG/Brix refractometer completely useless?
Post by: weithman5 on April 27, 2011, 10:58:14 PM
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.
Title: Re: SG/Brix refractometer completely useless?
Post by: enso on April 28, 2011, 12:21:10 PM
...free apps by the way.

Nice!  Now, you got a free iphone and a prepaid subscription to use it for me as well!  Oh, and we could use some cell service up here also...   ;D

Okay thanks folks.  Cant wait to play with it...  That's assuming I actually get what I asked for!   :D
Title: Re: SG/Brix refractometer completely useless?
Post by: oscarvan on April 28, 2011, 08:35:40 PM
OK Lucy..... 'splain to me why the same instrument is accurate on the Brix scale and not on the SG scale..... ???
Title: Re: SG/Brix refractometer completely useless?
Post by: Kit B on April 28, 2011, 08:59:52 PM
I have my doubts as to whether this issue is valid.
I mean...I'm sure there are some bogus products that are being made.
But, my buddy has one that seems quite valid.

Another friend & I have an ongoing debate about Brix vs SG.
He claims that it's impossible to have an ATC refractometer measure both.
I totally disagree.
Title: Re: SG/Brix refractometer completely useless?
Post by: glastctbrew on April 28, 2011, 09:00:30 PM
OK Lucy..... 'splain to me why the same instrument is accurate on the Brix scale and not on the SG scale..... ???

My guess, The instrument is designed for reporting brix.  To make it more appealing to home brewers and vintners they added an SG to one side of the scale.  Sounds great but whoever setup the printing of the scale used a faulty correlation factor.  It COULD read SG accurately but the SG scale in the display is off.
Title: Re: SG/Brix refractometer completely useless?
Post by: denny on April 28, 2011, 09:05:28 PM
He claims that it's impossible to have an ATC refractometer measure both.

What's his reasoning?
Title: Re: SG/Brix refractometer completely useless?
Post by: phillamb168 on April 29, 2011, 08:54:53 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?
Title: Re: SG/Brix refractometer completely useless?
Post by: enso on May 02, 2011, 06:37:06 PM
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!
Title: Re: SG/Brix refractometer completely useless?
Post by: Kit B on May 02, 2011, 09:00:11 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.
Title: Re: SG/Brix refractometer completely useless?
Post by: a10t2 on May 03, 2011, 02:13:15 PM
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. ;)
Title: Re: SG/Brix refractometer completely useless?
Post by: Kit B on May 04, 2011, 08:08:08 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.
Title: Re: SG/Brix refractometer completely useless?
Post by: tschmidlin on May 04, 2011, 09:04:40 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.
Title: Re: SG/Brix refractometer completely useless?
Post by: Kit B on May 05, 2011, 03:52:44 PM
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.
Title: Re: SG/Brix refractometer completely useless?
Post by: a10t2 on May 05, 2011, 05:32:43 PM
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. ;)