Just started using a refractometer, and trying to calculate ABV using a correction calculator. For a recent batch, SG measured with refractometer at room temperature was 1.049. FG measured with refractometer at room temperature was 1.025. In order to calculate ABV given the challenge of using a refractometer, is the following approach correct? Convert gravity to brix using http://www.brewersfriend.com/brix-converter. (SG = 12.1 and FG = 6.3). Enter starting brix and final brix at http://onebeer.net/refractometer.shtml to correct for the effect of the refractometer. (Adjusted FG = 1.010 and ABV = 5.1%.) Is there an easier way? Thanks
in a pinch https://www.northernbrewer.com/learn/resources/refractometer-calculator/, also included in most brewing software/spreadsheets
There are many refractometer calculators into which you put the two refractometer readings and out pops the OG/FG/ABV. Many of them are not very good. Google Sean Terrill's refractometer calculator or download BrewCipher (which uses Sean's formulae, with a slight usability enhancement). (BrewCipher is also an integrated brewing spreadsheet, so if you don't need or want that, Sean's standalone calculator is my recommendation.)
It seems to me you are reading the gravity scale on your refractometer instead of the Brix scale. The gravity scale on a refractometer is generally not as accurate as the Brix scale. So... You say you got readings of 1.049 and 1.025 on your refractometer. These readings are probably not the most accurate. So, look again inside the refractometer scope where the scales are next to each other. If you had used the Brix scale instead of gravity, did you actually get something closer to like 12.3 Brix and 6.3 Brix or something like that? I guess my real question is: what would the equivalent Brix reading have been exactly on YOUR refractometer for the 1.049 and 1.025 gravity readings that you recorded? Different refractometers have different scales for Brix vs. SG and they are NOT all the same, but the one consistent fact is that the Brix scale is more accurate and should be consistent from gauge to gauge, ignoring the SG scales completely. In future you might want to record Brix instead of SG as it's more accurate. After you figure out what the true original and final Brix readings were, then those need to be adjusted with a correction factor of 1.04 for wort. You can use either brewersfriend or Sean Terrill's calculators for that, but do make certain that you adjust with the 1.04. This is a factor determined experimentally by Sean Terrill with input from numerous homebrewers, and is an average across many gauges. In practice it should get you results accurate within 0.001 gravity points or maybe 0.002 at most. So, in your case, if my belief is true and you actually started with 12.3 Brix and it finished at 6.3 Brix, then including the factor of 1.04 using either brewersfriend or Sean Terrill's calculators (http://seanterrill.com/2012/01/06/refractometer-calculator/comment-page-1/), I get: 1.048 --> 1.012 = 4.5% or 4.8% ABV, depending which calculatory you trust more. Personally I think the answer for ABV is in between the two so I would say 4.7% because I use the formula (OG - FG) * 131 = 4.7%. Bottom line: Record Brix from now on, and adjust readings on those websites with a factor of 1.04, and that's all there really is to it.
Thanks guys. Using Sean Terrill's calculator and the brix readings from my refractometer, I'm coming up with 4.9%. Much easier and more accurate. Thanks.
