VikeMan
It ain't all burritos and strippers, my friend.
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- Aug 24, 2010
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Let’s have a heart to heart about refractometer Wort Correction Factor (WCF). My hope, though not necessarily my expectation, is to convince people that WCF is primarily intended to account for differences between Worts, and not differences between Refractometers (as I’ve very often seen stated).
Refractometers measure the concentration of “stuff” in solution. They do this by measuring the refraction of light passed through the sample solution. The sort of refractometers we homebrewers use have been set up to measure Sucrose solutions, which just means that the scale printed on the instrument corresponds the readings produced by sucrose solutions.
But, sucrose is something that the solids dissolved in wort are mostly not. Instead, wort contains various sugars, unfermentable dextrins, proteins, lipids, etc. And each non-sucrose substance (most, anyway) has a refractive index that’s different from the refractive index of sucrose.
Thus, WCF. Dividing the refractometer reading by the WCF gives a better estimate of the true concentration of sugars/dextrins in the wort, accounting and correcting for the differences in refractive index.
But wait! Don’t different worts have different mixes of sugars, dextrins, etc., and so shouldn’t the WCF be different for each wort? You betcha it should. But as a practical matter, most people don’t have the time or inclination to experiment with, record, and analyze comparisons of refractometer readings vs. hydrometer readings to find the best WCFs for each individual recipe. So most folks grab a “default” WCF (1.04 or 1.03 are pretty safe) and use it. But it’s still a factor used to get a better approximation of the true gravity of the wort, accounting (in an average/default sort of way) for the previously mentioned differences in those refractive indexes. And it has nothing to do with the differences between one sucrose scaled refractometer and another sucrose scaled refractometer.
So where does the notion that WCF is intended to account for the differences between refractometers come from? I’m not 100% sure. About 10 years ago, Kai blogged about his wonky refractometer that needed a non-typical WCF. What he was really doing (reading between the lines) was adapting a typical WCF to account for his wonky refractometer, i.e. there were two factors disguised as one. I’ll take a minute to say that Kai has done as much for homebrew science as anyone, and far more than most. I don’t think he meant for people to think that WCF is essentially a factor to account for differences between refractometers, but I fear a lot of people may have taken it that way. So much so that it’s not hard to find spreadsheets intended for the recording of refractometer and hydrometer readings over many batches of wort, and then compute an average WCF “for your refractometer.” What these spreadsheets are really doing is computing an average WCF for the worts that particular brewer tends to make. That said, if the refractometer itself is inaccurate (or not calibrated), then Kai’s wonky-refractometer-adjustment will be embedded in the average computed. Perhaps the refractometer calculators should include two correction factors… one for wort (the WCF) and one for faulty refractometers. The latter could default to 1.0 for properly functioning refractometers. I’m only partly kidding.
But wouldn’t two different “sucrose” refractometers measure wort differently from each other? After all, they are sucrose refractometers, not wort refractometers, right? Well, no. Not if they are accurate and calibrated. As previously hinted at, the refractometer measures the diffraction of light, and doesn’t “know” that it’s referenced, via the printed scale, to sucrose solutions. Imagine two accurate and calibrated refractometers that both measure the same sucrose solution at, say, 15 brix (about 1.061 SG). Knowing how refractometers function, do we think that an equivalent single mash-derived WORT of about 1.061 SG would give two different measurements between these two refractometers? Of course not. But that’s what you’d have to believe if you also believe that two different accurate and calibrated “sucrose” refractometers need different WCFs from each other.
Refractometers measure the concentration of “stuff” in solution. They do this by measuring the refraction of light passed through the sample solution. The sort of refractometers we homebrewers use have been set up to measure Sucrose solutions, which just means that the scale printed on the instrument corresponds the readings produced by sucrose solutions.
But, sucrose is something that the solids dissolved in wort are mostly not. Instead, wort contains various sugars, unfermentable dextrins, proteins, lipids, etc. And each non-sucrose substance (most, anyway) has a refractive index that’s different from the refractive index of sucrose.
Thus, WCF. Dividing the refractometer reading by the WCF gives a better estimate of the true concentration of sugars/dextrins in the wort, accounting and correcting for the differences in refractive index.
But wait! Don’t different worts have different mixes of sugars, dextrins, etc., and so shouldn’t the WCF be different for each wort? You betcha it should. But as a practical matter, most people don’t have the time or inclination to experiment with, record, and analyze comparisons of refractometer readings vs. hydrometer readings to find the best WCFs for each individual recipe. So most folks grab a “default” WCF (1.04 or 1.03 are pretty safe) and use it. But it’s still a factor used to get a better approximation of the true gravity of the wort, accounting (in an average/default sort of way) for the previously mentioned differences in those refractive indexes. And it has nothing to do with the differences between one sucrose scaled refractometer and another sucrose scaled refractometer.
So where does the notion that WCF is intended to account for the differences between refractometers come from? I’m not 100% sure. About 10 years ago, Kai blogged about his wonky refractometer that needed a non-typical WCF. What he was really doing (reading between the lines) was adapting a typical WCF to account for his wonky refractometer, i.e. there were two factors disguised as one. I’ll take a minute to say that Kai has done as much for homebrew science as anyone, and far more than most. I don’t think he meant for people to think that WCF is essentially a factor to account for differences between refractometers, but I fear a lot of people may have taken it that way. So much so that it’s not hard to find spreadsheets intended for the recording of refractometer and hydrometer readings over many batches of wort, and then compute an average WCF “for your refractometer.” What these spreadsheets are really doing is computing an average WCF for the worts that particular brewer tends to make. That said, if the refractometer itself is inaccurate (or not calibrated), then Kai’s wonky-refractometer-adjustment will be embedded in the average computed. Perhaps the refractometer calculators should include two correction factors… one for wort (the WCF) and one for faulty refractometers. The latter could default to 1.0 for properly functioning refractometers. I’m only partly kidding.
But wouldn’t two different “sucrose” refractometers measure wort differently from each other? After all, they are sucrose refractometers, not wort refractometers, right? Well, no. Not if they are accurate and calibrated. As previously hinted at, the refractometer measures the diffraction of light, and doesn’t “know” that it’s referenced, via the printed scale, to sucrose solutions. Imagine two accurate and calibrated refractometers that both measure the same sucrose solution at, say, 15 brix (about 1.061 SG). Knowing how refractometers function, do we think that an equivalent single mash-derived WORT of about 1.061 SG would give two different measurements between these two refractometers? Of course not. But that’s what you’d have to believe if you also believe that two different accurate and calibrated “sucrose” refractometers need different WCFs from each other.
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, my "factor" based on my experimentation here for an average wort or beer with my refractometer at my house with my process and my system is not 1.03-1.04, but rather 1.00. YMMV
