This is something I’ve been meaning to do for a long time, but kept finding excuses to put off. It uses the simplified cubic polynomial derived in Refractometer FG Results. Please visit that post for more information.
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Refractometer Calculator21 comments to Refractometer CalculatorLeave a Reply |
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[...] (finally) written a PHP version of the basic FG calculation, so that people can use it without downloading the spreadsheet. [...]
Thanks for all the work with the Refractometer Calculator & putting a PHP version on your website. Very useful!
Jerry
[...] [...]
This is extremely helpful!! No more tedious math!! Thank you very much for putting this up!
Compared the last 5 brews I did with hydrometer and More beer refractometer program results. On all of them your OG specific gravity conversion from the brix reading was 2 (or so) sp gravity points lower than my hydrometer and the More beer values. These two were routinely within .5 sp gravity points. All the Fg calculations were spot on though!
Jack,
It sounds like the difference in OG you’re seeing could be due to the wort correction factor (1.04 by default). Are you applying a correction before using the MoreBeer sheet? If memory serves, it doesn’t have that capability.
At any rate, I’m glad it’s working out for you.
Sean
[...] various equations (good reading if you like that stuff). Probably the most accurate out there IMO. http://seanterrill.com/2012/01/06/refractometer-calculator/ GA_googleFillSlotWithSize("ca-pub-3927874040083090", "HomeBrewTalk_Forum_336x280_BTF", 336, 280); [...]
[...] I'm using Sean Terrill's refractometer FG calculator. Here's his website if your interested: http://seanterrill.com/2012/01/06/refractometer-calculator/ Anyway, with an OG of 12.86 brix and an FG of 7.06 brix according to Sean's calculator, the actual [...]
[...] an online calc for that or manual? There are several, most require a Brix reading. Here's one: http://seanterrill.com/2012/01/06/refractometer-calculator/ Your actual gravity is probably around 1.018 or 1.019 right now with the correction factor. Which [...]
[...] I just learned that it is always a good idea to check the correction factor that applies to your refractometer. A commonly accepted correction factor for converting a refractometer’s Brix reading to a hydrometer Plato reading is 1.04. I was always under the impression that the Brix reading has to be multiplied with this value, which works for me, but Sean Terril pointed out to me that the commonly accepted formula divides the Brix value by this correction factor to covert to a Plato reading. (Refractometer Calculator) [...]
Thanks for the calculator. Used it for my last two brews.
(while my hydrometer gently weeps)
Hi, thanks for the calculator. When a hydrometer sees me coming, it leaps screaming off the mantel to a glassy death.
I bought the refractometer two brews ago, and went through the old “how come it stopped fermenting?” when I took a reading I was expecting to be 1.010, but came out as 1.020. When the Internet told me how wrong I was to expect the device to make a reading in the presence of alcohol, I was already feeling guilty about the soon to be purchased and trashed hydrometer when I heard the show with James Spencer.
I don’t have a hydrometer :-) to check against, but the two low gravity beers I brewed in March seem to follow what I expected to get from OGs and observation when plugged into the calculator.
Hydrometers everywhere thank you,
Richard.
[...] calculator http://seanterrill.com/2012/01/06/refractometer-calculator/ GA_googleFillSlotWithSize("ca-pub-3927874040083090", "HomeBrewTalk_Forum_336x280_BTF", 336, 280); [...]
[...] this: http://seanterrill.com/2012/01/06/refractometer-calculator/ -d GA_googleFillSlotWithSize("ca-pub-3927874040083090", "HomeBrewTalk_Forum_336x280_BTF", 336, [...]
Hi Sean, great work with all the calculations. How reliable do you feel this is?
I generally use a refractometer pre-boil and hydrometer post ferment as I haven’t felt I could trust the refractometers for measurements where alcohol was involved.
I was using your spreadsheet and keep track of my last 5 batches or so.
I currently have a Saison fermenting pre-boil was 15.2 brix, I measured the other day and I had 6.1brix, I also tested with my hydrometer and got 1.016sg.
Plugging the brix numbers in your calculator gives me a 1.008sg and approx 6.5% abv which is right where i want it. Putting the same numbers plus the hydrometer measurement in the spreadsheet gives me an abv of 5.5%.
Any theories?
Phillip,
The standard deviation for the 68 beers tested was 1.3 “points”. So if we make the assumption that those beers were a representative sample, then we can expect essentially all (99.7%) FGs to fall within 4 points of the predicted value. In reality, it was 97% for this data set, but that’s close enough.
So being 8 points off is highly unlikely. Have you calibrated the hydrometer and refractometer recently?
It could be that using a saison strain results in a large proportion of higher alcohols, or some other compound(s) that is/are throwing off the refractive index. If the correlation has given you good results when using other strains, I’d lean more towards that explanation.
Sorry I don’t have a definitive answer for you.
Sean
Hi Sean thanks for the reply, I went back and did a single point calibration of my hydrometer and my refractometer using distilled water at approx 68F. My refractometer was reading 0 which was good news however my hydrometer was reading between 3-4 points on the high side. This brings my readings inline with your calculations.
One more question, I put my OG in your calculator as 15.19 brix all the charts I’ve seen have this value in SG as 1.062, your calculator has it as 1.0594, where does that difference come from. I use the fermsoft grav brix chart for conversions mostly. http://www.fermsoft.com/gravbrix.php
Thanks again
Phillip.
Phillip,
Aha! This one’s easy. 15.2°Bx is in fact 1.062 SG, and if you were converting hydrometer readings it would be just that simple. Remember, though, that a refractometer doesn’t actually measure density – it measures the refractive index. That’s why a correction factor (1.04 by default) needs to be applied when using a refractometer with beer wort.
Sean
I’ve used your spread sheet for several batches. Currently I’m monitoring an open fermentation of a Russian Imperial Stout. OG was 25.3 Br, converting to ~1.103. I’m about 48 hours into fermentation and took a refractometer measurement for fun. It’s about 19 Br (fuzzy with yeast I’m sure, but the best fit for what I see). Entering that into your calculator and the spread sheet, the new cubic calculates 1.125 and the new linear calculates 1.043. Obviously the cubic is having a problem with this data (the 2 equations get close to each other in the 13-14 Br range), but how close is the linear calculation. It’s not that important right now, but it is interesting.
At this point, I wouldn’t assume that either correlation is giving good results. They won’t work below about 60% ADF, and you’re at the high end of the OG range as well.
[...] use this one: http://seanterrill.com/2012/01/06/refractometer-calculator/ Look here for more information about it: [...]