Used the refractometer- now a question

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BmillaTheBrewzilla

BmillaTheBrewzilla

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I just recently received my specific gravity refractometer (with ATC) and I used it for brewing last night. It shows both specific gravity and brix. One thing I noticed is this: the brix measurement doesn't seem to match up with the specific gravity when compared to the online calculators that are available.

For example: on my refractometer, a brix reading of 12.8 matches up with a specific gravity of 1.050. However, when I enter 12.8 on http://www.onebeer.net/refractometer.shtml (or any other calculator I've found), I get a specific gravity of 1.052. Not a huge difference, but you'd think the scale on the refractometer would match up. What's going on here??? Any ideas? :confused:
 
There is a correction factor that is usually applied when going from brix on a refractometer to SG for beer. I don't think I've ever used a refractometer that read anything but brix, but I calibrated mine to my hydrometer readings before I started trusting the readings from it. And even then the readings will vary from batch-to-batch. I use it as a guideline but it's not a definitive reading of the gravity IMO unless you calibrate it every batch.

I use beersmith which has tools built-in to calculate and incorporate the correction factor, but there's spreadsheets floating around on this site with the equations. It's not tough just a simple scaling factor.
 
+1 on wierdboy comments.

And it pretty much sums up why I find the thing almost useless for me. I much prefer my $5 hydrometer.
 
I may not have phrased my confusion clearly. I have a spreadsheet that does the correction between brix and specific gravity. I have BeerSmith. So I understand how to go from brix to specific gravity.

My refractometer is the RSG-100/ATC, which includes both brix AND specific gravity when you take a reading. I'm wondering if there is a problem with the way my refractometer was designed. Because there is not agreement between its brix readings, its specific gravity readings, and the specific gravity readings I should be getting based on the refractometer's brix readings (based on the numerous conversion helpers based on the scale factor).

Does anyone else have the same refractometer? I'm wondering if it is a better idea to ignore the specific gravity readings on it and just use the brix with the scale factor.
 
Those SG/Brix refractometers are incorrect - the SG scale does not match up with the math when you climb up the SG scale, around 1.050. It slips more out of sync as you get higher. The brix chart should still be fine though, so you can still use that. But I would double check the math on the SG chart if you use that as well.
 
Jipper said:
Those SG/Brix refractometers are incorrect - the SG scale does not match up with the math when you climb up the SG scale, around 1.050. It slips more out of sync as you get higher. The brix chart should still be fine though, so you can still use that. But I would double check the math on the SG chart if you use that as well.
Click to expand...

That definitely would explain why I was confused. At any rate- the refractometer is a pretty useful tool when using the conversion from brix. Thanks!
 
Jipper said:
Those SG/Brix refractometers are incorrect - the SG scale does not match up with the math when you climb up the SG scale, around 1.050. It slips more out of sync as you get higher. The brix chart should still be fine though, so you can still use that. But I would double check the math on the SG chart if you use that as well.
Click to expand...

Jipper, so what I hear you telling me is that the SG/Brix refractometer I bought up there a few months back doesn't actually work!! :mad: ;)

Seriously though, the thing works great, but I have also noticed that the numbers don't seem to match up exactly. I guess now I know why...and knowing IS half the battle. :D
 
I just plugged 12.8 Brix into the ProMash utility for converting to SG using the default 1.040 correction factor and it comes up with 1.04967, or rounded off it would be 1.050.
I have no idea why all these calculators ans spreadsheets come up with such widely varying numbers. I would expect them to be much closer than that. I do realize that the formulas are only approximations, but WTF?
 
Catt22 said:
I just plugged 12.8 Brix into the ProMash utility for converting to SG using the default 1.040 correction factor and it comes up with 1.04967, or rounded off it would be 1.050.
Click to expand...
A little :off:, but how do you get to this utility in ProMash?

I've had ProMash for the last few years and was unaware that this was in there.
 
I brewed last weekend with my specific gravity refractometer. When I took samples to test I would test it 3 times in a row and every time I got a different reading. At the end of my boil I actually got readings of 1.071, 1.081, 1.076, and 1.073. That is a pretty damn big difference. Doesn't seem to be very accurate at all from my findings.
 
Walker said:
A little :off:, but how do you get to this utility in ProMash?

I've had ProMash for the last few years and was unaware that this was in there.
Click to expand...

There are some drop down menus across the very top of the main ProMash menu. Pull down the one marked Utilities, then pull down the Refractometer menu, then select Raw Wort Gravity. You can change the correction factor if desired. To do that, pull down the Options menu and select System Settings, then select Instrument Calibration from that menu.
 
steinsato said:
I brewed last weekend with my specific gravity refractometer. When I took samples to test I would test it 3 times in a row and every time I got a different reading. At the end of my boil I actually got readings of 1.071, 1.081, 1.076, and 1.073. That is a pretty damn big difference. Doesn't seem to be very accurate at all from my findings.
Click to expand...

I've had similar experiences. What I think may be happening is that suspended particulates (hop debris, trub etc) are interfering with the readings. I found that I get more consistent reading if I take a sample in a small measuring cup and let it stand for a few minutes before checking the gravity. This allows the bulk of the larger particulates to drop out. I still take several readings and only trust the results when I can get two subsequent readings to agree within a few tenths of a degree brix. I always take a hydrometer sample before pitching to verify my OG. I like to see this agree with the corrected refractometer reading within a couple of SG points and it usually does. I used to think that wort stratification in the boil kettle was the problem, but I could not believe that the boil would not have everything pretty uniformly mixed up, so I've abandoned that theory in favor of the particulates causing the problem.
 
Huh I have not had problems with a lot of variation in different readings. I usually get the same reading every time if I do multiple samples with my refractometer.

Maybe it's a process thing? I can't imagine there'd be so much variability in an optical device like that.

I guess it could be particulates, but samples are quite small, only a couple of drops of wort. If you got a big honkin piece of hop or trub in there it would be pretty noticeable I'd think.
 
steinsato said:
I brewed last weekend with my specific gravity refractometer. When I took samples to test I would test it 3 times in a row and every time I got a different reading. At the end of my boil I actually got readings of 1.071, 1.081, 1.076, and 1.073. That is a pretty damn big difference. Doesn't seem to be very accurate at all from my findings.
Click to expand...

What was the temperature of the wort? I haven't seen an error quite that large, but if you aren't doing something to minimize evaporation of a sample that's near boiling you won't be able to get an accurate reading. At a bare minimum, I've found that I need to get the syringe out of the wort, onto the plate, and get the cover slip closed in less than 2 seconds. Since I feel like that's just asking for an accident, I dunk the syringe, upside down, in ice water for a few seconds to cool the sample down.

Those SG/Brix refractometers are incorrect - the SG scale does not match up with the math when you climb up the SG scale, around 1.050.
Click to expand...

Thanks for verifying that - I'd been trying to figure out if the pictures posted online were correct for a while now. It looks like they used a "multiply by four" rule, rather than an actual Brix-SG correlation. :rolleyes:
 
Catt22 said:
I've had similar experiences. What I think may be happening is that suspended particulates (hop debris, trub etc) are interfering with the readings. I found that I get more consistent reading if I take a sample in a small measuring cup and let it stand for a few minutes before checking the gravity. This allows the bulk of the larger particulates to drop out. I still take several readings and only trust the results when I can get two subsequent readings to agree within a few tenths of a degree brix. I always take a hydrometer sample before pitching to verify my OG. I like to see this agree with the corrected refractometer reading within a couple of SG points and it usually does. I used to think that wort stratification in the boil kettle was the problem, but I could not believe that the boil would not have everything pretty uniformly mixed up, so I've abandoned that theory in favor of the particulates causing the problem.
Click to expand...

I have the RSG-100ATC refractometer.

I must admit I have had these problems too. Another brewer visited while I was brewing and he couldn't believe how wildly different the results can be - we took about 5 readings - about 2 were the same, and the other 3 were significantly different.

So different that it isn't something I rely on - I use my hydrometer now. PITA and all my dosh invested in this piece of junk.

I'll chat to the supplier see if anyone is returning them, and if I can too, else I'll probably flick it with a caveat as above.

Dave.
 

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