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BVilleggiante 05-21-2012 07:38 PM

Accuracy of MoreBeer's Refractometer Reading Spreadsheet For Alcohol?
 
I used MoreBeer's Spreadsheet that is supposed to correct your refractometer reading when alcohol is present to give you the correct readout. I was expecting a FG of 1.016 but got 1.007 instead. Can anyone confirm the accuracy of this spreadsheet or did my FG just drop below what I was expecting?

rhamilton 05-21-2012 07:42 PM

100% unreliable for post-fermentation readings. Two refractometers showed 1.40 for two of my brews last week, so I spent two days freaking out and messing with the brews. Two different hydrometers later confirmed the gravity @ 1.012 (right on target)

Long story short; only a hydrometer will give you correct FG readings.

BVilleggiante 05-21-2012 08:15 PM

And let me just confirm what you're saying here. Did you take your readings and put them into the MoreBeer sheet that is supposed to correct the refractometer reading when it has alcohol in it?


Quote:

Originally Posted by rhamilton (Post 4104399)
100% unreliable for post-fermentation readings. Two refractometers showed 1.40 for two of my brews last week, so I spent two days freaking out and messing with the brews. Two different hydrometers later confirmed the gravity @ 1.012 (right on target)

Long story short; only a hydrometer will give you correct FG readings.


rhamilton 05-21-2012 08:56 PM

Yep. Even after correction, it was a full .030 off on both batches. Confirmed with two different refractometers, one digital.

Some people get away with using the correction sheet but eventually you'll experience what I did and it'll be way way way off. Now the funny thing is, the third batch I measured with the refractometers were spot on and read exactly the same as the hydrometer -- so it works sometimes on some batches, but it's not an accurate tool for reliably measuring the FG all the time.

From my conversations with other refractometer users:

Use the refractometer to establish OG
Use the refractometer to determine when fermentation has stopped, 3x consecutive days of the same reading.
Then use the hydrometer to establish the actual FG reading.

davepeds 11-30-2012 04:28 AM

what about this?
http://www.homebrewtalk.com/f128/est...ometer-317679/

I'm doing one gallon batches now, instead of the 5 & 10 gallons. Losing 75ml multiple times over is unacceptable - so I have to figure something else out!

Golddiggie 11-30-2012 04:40 AM

Perhaps, using CHEAP refractometers you have issues. I don't. Mine are dead-nuts accurate time and again. You DO need to make sure you have ATC refractometers, and you've calibrated them recently (to the ambient temp). Once you've done that, as long as you're reading it correctly, you'll get accurate readings that can be adjusted for the presence of alcohol.

I reserve 4 Dram size vials of my OG sample and then pull a matching size for the FG sample, of every brew. This allows me to get readings from both solutions at the same time, recording the readings. I've found that if you don't correctly read either measure, your numbers will be off (on the conversion spreadsheet). It's human error, not the tools there. Blame the monkey, not the wrench. :eek:

BTW, rhamilton, "only a hydrometer will give you correct FG readings." is 100% BS... A CHEAP refractometer OR hydrometer is suspect by it's very nature. Get a good version of either and you'll do fine. There are PLENTY of threads from people with inaccurate hydrometers.

diS 11-30-2012 07:45 AM

Same here, I don't rely on refractometer FG reading any more.
On my last batch refractometer reads 1.012 and hydrometer 1.018, but I use el-cheapo ebay refractometer.

Golddiggie 11-30-2012 03:06 PM

For the record, my refractometers were almost a C note each. I have three of them. :eek: One reads 0-32 in .2 increments, another 0-20 in .1 increments and another 30-60 in .2 increments. That last one is so I can get a measure of really high sugar content solutions. Such as if I wanted to do a 50/50 mix of honey and water to get the sugar level in it. It doesn't go quite high enough to do it without making a solution. :( Maybe the next one I get will. :D

ajf 11-30-2012 07:19 PM

Quote:

Originally Posted by Golddiggie (Post 4635097)
Perhaps, using CHEAP refractometers you have issues. I don't. Mine are dead-nuts accurate time and again. You DO need to make sure you have ATC refractometers, and you've calibrated them recently (to the ambient temp). Once you've done that, as long as you're reading it correctly, you'll get accurate readings that can be adjusted for the presence of alcohol.

I reserve 4 Dram size vials of my OG sample and then pull a matching size for the FG sample, of every brew. This allows me to get readings from both solutions at the same time, recording the readings. I've found that if you don't correctly read either measure, your numbers will be off (on the conversion spreadsheet). It's human error, not the tools there. Blame the monkey, not the wrench. :eek:

BTW, rhamilton, "only a hydrometer will give you correct FG readings." is 100% BS... A CHEAP refractometer OR hydrometer is suspect by it's very nature. Get a good version of either and you'll do fine. There are PLENTY of threads from people with inaccurate hydrometers.

With all due respect, what you are saying is wrong.

A refractometer does not measure specific gravity, it measures the refractive index of a solution and usually translates this into degrees Brix which is a representation of the amount of sucrose dissolved in that solution. (1 degree Brix is 1 gram of sucrose dissolved in 100 grams of solution). The Brix reading is then converted to an estimate of S.G. by applying the formula "Specific gravity = (Brix/(258.6-(Brix/258.2)*227.1))+1"

But a beer wort contains mostly maltose, and very little sucrose, and this results in an incorrect Brix reading being reported when measuring wort rather than a sucrose solution. So if the refractometer reads 10 Brix when measuring a pure sucrose solution, the S.G. of that solution will be 1.040

If you make a wort that reads 10 Brix, and measure the S.G. of that wort, you will find that it is closer to 1.038, but the actual gravity will depend on the sugars dissolved in that wort.

If your conversions are "dead-nuts accurate time and again" then that is either because you are making worts with identical compositions, or because you are not checking the results with a hydrometer.

As for the MoreBeer spreadsheat, I put the refractometer readings in from a recent brew where I measured the O.G. and F.G. with both the refractometer and hydrometer. Here are the results measurements I took:
Pre-fermentation Brix 14.75, O.G. 1.056
Post-fermentation Brix 6.75 F.G. 1.013
Here's the results I got from the MoreBeer spreadsheet
14.75 pre-fermentation Brix is rounded up to 14.8 and translated to 1.060 (4 points high)
6.75 post-fermentation Brix reports 1.007 F.G. (6 points low)

Using Promash, the pre-fermentation Brix translated to the measured O.G. correctly.

-a.


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