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- Feb 16, 2012
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So, I've been brewing beer and making wine for more than 25 years. Definitely broke a few hydrometers and wasted gallons of precious fluids during that time. That all led to eventually buying a refractometer about five years ago. I like the utility of using it and the accuracy of seeing a sharp line of demarcation rather than trying to read a meniscus and calculating temperature corrections (not to mention dumping samples down the drain) when using a hydrometer.
But I always wondered about how accurate my refractometer actually is. I did calibrate with distilled water @ 60F to confirm "0" refractive index and calculated my device's Wort Correction Index to be exactly the widely accepted value of 1.04, so I feel my Original Gravities are spot on. I always get my samples to "room temperature" before taking readings both before, during and after fermentition. The issue, however, are calculations made with the presence of alcohol in the sample.
The Brewer's Friend refractometer calculator does an excellent job of applying some advanced math into the task determining the non-linear values of alcohol on refractive indices. My question is, how accurate is the Wort Correction Index of 1.04 (corrected for maltose vs. glucose) after the majority of the sugars present in the original wort have been converted into CO2 and alcohol?
Shouldn't I be using a sliding exponential scale of WRI factor indices to determine gravity during fermentation and once FG has been reached? Sure, I could dust off the old hydrometer jar and take readings the old fashioned way, but that defeats the purpose of using a refractometer in the first place.
Before I get accused of "measuring with a micrometer and cutting with an axe", the scale errors become significant at gravities > 1.065, according to the literature. More and more of my brews are in this range of OG. At about 1.075 the ABV error is 0.5% ABV, so your 7.4% Strong Ale may actually only be a 6.9% India Pale Ale.
Any thoughts on this?
Brooo Brother
But I always wondered about how accurate my refractometer actually is. I did calibrate with distilled water @ 60F to confirm "0" refractive index and calculated my device's Wort Correction Index to be exactly the widely accepted value of 1.04, so I feel my Original Gravities are spot on. I always get my samples to "room temperature" before taking readings both before, during and after fermentition. The issue, however, are calculations made with the presence of alcohol in the sample.
The Brewer's Friend refractometer calculator does an excellent job of applying some advanced math into the task determining the non-linear values of alcohol on refractive indices. My question is, how accurate is the Wort Correction Index of 1.04 (corrected for maltose vs. glucose) after the majority of the sugars present in the original wort have been converted into CO2 and alcohol?
Shouldn't I be using a sliding exponential scale of WRI factor indices to determine gravity during fermentation and once FG has been reached? Sure, I could dust off the old hydrometer jar and take readings the old fashioned way, but that defeats the purpose of using a refractometer in the first place.
Before I get accused of "measuring with a micrometer and cutting with an axe", the scale errors become significant at gravities > 1.065, according to the literature. More and more of my brews are in this range of OG. At about 1.075 the ABV error is 0.5% ABV, so your 7.4% Strong Ale may actually only be a 6.9% India Pale Ale.
Any thoughts on this?
Brooo Brother