Refractometer readings in BRIX

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bobtheUKbrewer2

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I use software obtained via this forum to convert refractometer readings to BRIX, and have noticed that if OG is 15 BRIX a FG of 5 BRIX gives a certain specific gravity. However if OG = 10 BRIX 5 BRIX is now a different specific gravity. Any thoughts?
 
5 brix will always be 1.020-ish. However what I'm wondering is are you using a refractometer to measure FG? Because if you are you'll need to use a formula to figure out what it really is because the alcohol will throw the reading off.

I don't personally use a refractometer but from what I've read on here, some people report that even with the corrections it's still not entirely accurate for FG.
 
I just posed this question to my L.H.B.S and the old guy has been doin brews for a very long time he says refractometer is def no good for FG.
 
As long as you have the original gravity and a good calculator (beersmith) a refractometer for FG works perfectly! I haven't used a hydrometer in over a year...
 
jbsengineer said:
As long as you have the original gravity and a good calculator (beersmith) a refractometer for FG works perfectly! I haven't used a hydrometer in over a year...
Click to expand...

I've never found any of those formulas or calculators to work well for FG. They seemed to work great until I attempted to verify the reading with a hydrometer.
 
gbx said:
I've never found any of those formulas or calculators to work well for FG. They seemed to work great until I attempted to verify the reading with a hydrometer.
Click to expand...

I should also mention I use a digital refractometer. I found I was inaccurate trying to pinpoint the line in a standard refractometer. After I calibrated my hydrometer and testing pre and post fermentation with the digital I couldn't find a difference.
 
bobtheUKbrewer2 said:
I use software obtained via this forum to convert refractometer readings to BRIX, and have noticed that if OG is 15 BRIX a FG of 5 BRIX gives a certain specific gravity. However if OG = 10 BRIX 5 BRIX is now a different specific gravity. Any thoughts?
Click to expand...

The software in question is used to offset the error created by the alcohol in the sample. A higher Brix OG for the same Brix FG suggests that there is more alcohol in the sample and requires more error correction.
 
What he said. Refractometer until the wort goes in the fermenter. Hydrometer to check FG. That is all.
 
great app on the iPhone, BrixCalc. Works like a charm. Many have tested OG and FG with the hydrometer as a comparison, and the error from reading the hydrometer would offset any error in the differences between the two. In higher gravity beers the difference becomes greater and might require a hydrometer sample.
 
A higher Brix OG for the same Brix FG suggests that there is more alcohol in the sample and requires more error correction.

The higher BRIX OG gives a DIFFERENT FG for the SAME final BRIX reading. The spreadsheet I am using "allegedly" has the corrections built in. The final gravity allegedly measures unfermented "sugars" and unfermentable "compounds" but cannot give this accurately because alcohol with a DENSITY of less than 1.00 is part of the final liquid. The corrections estimate the FG if there were no alcohol present, IMHO. So a hydrometer is the most inaccurate, surely?
 
1.001843-0.002318474*(A$8)-0.000007775*(A$8^2)-0.000000034*(A$8^3) +0.00574*($A12)+0.00003344*($A12^2)+0.000000086*($A12^3)

A8 = original brix
A12 = brix reading part way through fermentation

this is my formula - I obtained it from this forum
 
I have now amended my formula to Chris's latest one.

OG 15 BRIX FG 5 BRIX is equal to 1.005
OG 10 BRIX FG 5 BRIX is equal to 1.010

I am a little perplexed.....
 
I just posted about the same topic, go with a hydrometer for sure on the FG. Much easier then doing the math using a refractometer.
 
Doing the Math is easy as I use an Excel spreadsheet to record each brew, including a graph (chart) of SG versus time, this shows clearly the end of fermentation.

I am thinking about taking some liquor after the mash, and measuring OG in BRIX, and getting some 88% vodka, calculating how much alcohol is formed from "a specific weight" during fermentation, then diluting the wort with tap water by "an amount" and adding "an amount" of Vodka before measuring the SG in BRIX. I can do this say 5 times to replicate the ongoing fermentation and then use polynomial solving software to give me the formula.
 
bobtheUKbrewer2 said:
Doing the Math is easy as I use an Excel spreadsheet to record each brew, including a graph (chart) of SG versus time, this shows clearly the end of fermentation.

I am thinking about taking some liquor after the mash, and measuring OG in BRIX, and getting some 88% vodka, calculating how much alcohol is formed from "a specific weight" during fermentation, then diluting the wort with tap water by "an amount" and adding "an amount" of Vodka before measuring the SG in BRIX. I can do this say 5 times to replicate the ongoing fermentation and then use polynomial solving software to give me the formula.
Click to expand...

Yes, that is much simpler than floating a glass bobber in a tube to measure how far it sinks. :drunk:

I love my refractomer and use it at dozens of stages on brew day. But after my wort goes into the fermenter it gets put away and I use a thief and hydrometer.
 
The Brix scale is designed to use refraction of light to measure the sugar content of a simple solution of sugar and water. Once there is alcohol -- or even darker grains -- in your sample, you're not using the scale to measure what it was intended to measure. So you end up needing to use a complex formula to interpolate based on other peoples' data.

I like my refractometer, but there's really no substitute for a hydrometer. And this from a guy whose name is Brix.
 
OK folks - a hydrometer measures (for a sugar solution only) the ratio of the weight of 1 ml of solution to 1 ml plain water.

But 1 ml of 4% alcohol solution in water DOES NOT weigh 1 gram, it weighs less than a gram. So the hydrometer (in such a solution) is able to displace MORE solution, ie it sinks deeper, and gives you a reading that is too low.

The maths and chemistry is too much for me, can anybody say how to correct the hydrometer reading, please?
 
No takers then. If I measure the SG of a 4% alcohol solution, that should give me my correction factor.
 

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