Hi,
There are MANY on-line brewing tools and calculators but only one (as far as I know) implements improved method of Refractometer Correction Reading calculation.
Results (Hydrometer readings vs Sean Terrill correction vs Petr Novotný correction) can be seen on attached graph. As you can see Improved Formula returns correct values even for fermenting (not only fully fermented) wort.
Interesting… I signed up (you need to sign up to use the tool) because I noticed discrepancies between refract vs. hydro on my last batch using Sean’s calculator, but I’ll need quite a bit more data on subsequent batches to determine which tool I prefer. Thanks for sharing!
One thing the Czech tool does not do is calculate specific gravity, not at all. To do that, I still end up going back and forth to Sean’s calculator. If that could be added, it would be a more useful tool.
I can’t read Czech, how many beers has this been testing with? My experience with refract is that it gets thrown off by some oils as well as ongoing fermentation, grist with high % of oats for example, or highly hopped beers, will cause the refract to deviate more from the hydrometer readings.
How does this compare to the “traditional” refractometer calculator that promash, and other software, used to have for calculating the gravity of fermenting wort? The reason Sean came up with the new formula specifically for final gravity, using empirical data, was because that old equation often underestimated FG.
[quote]It’s probably because his equation wrong, “grafted” to the experimental data. He used merely data for “well-fermented beer”, and thus had little and poorly stratified data, which culminated poorly designed coefficients.
[/quote]
No, it’s because in the data set I was working with (89 data points from eight breweries - two of them “professional”, since that apparently carries some weight), it wasn’t possible to generate a mathematically rigorous curve that fit both fermenting wort and gave hydrometer-level precision (±0.05°P) for FG.
@a10t2 Who are you quoting there? I don’t see that reply anywhere.
Wort correction factors vary for every beer, so unless you’re measuing the OG with both a refractometer and a hydrometer at reference temperature then you’re unlikely to get an accurate WCF. If you are, doesn’t that sort of defeat the purpose of it?
FYI: you can read a little bit about this “new” approach in latest Zymurgy issue (July/August 2017), article “Revisiting the Refractometer by Petr Novotny”.
My own data to date has confirmed the Novotny formula for calculating SG from Brix is a good one. Not necessarily “better” than Terrill’s, but a bit different, and valid in its own right.
And the most accurate FG formula for me is…
None of the above.
Actually, it’s the one that Terrill refers to as the “Old Cubic”, for which I forget the source but so far it seems closest on the average. Not perfect either, but close on the average.
To be fair, some of my data is for very high gravity beers, for which no formulae are very accurate – they are all calculating FG values 0.003-0.006 higher than my hydrometer. For example there is one beer where my OG was 1.098 as measured by hydrometer (and original Brix was 23.2). Calculated FG for final Brix 12.9 and correction factor 0.99 (yes, NOT 1.04) was anywhere 1.026-1.029 depending on the formula, but my hydrometer said 1.023. So, not a big deal – next time I make a huge beer of OG >1.090, I’ll expect to have to subtract a few points from the calculated FG if I skip the hydro and just use refract. Close enough.
For me, ultimate near-exclusive use of refractometer is desirable, as I am a small batch brewer and would prefer to get 14-15 bottles out of a batch rather than just a 12-pack from too many hydro samples. For those doing 5 or 10 gallons, sure, I get why you might not care. But I do.
The “Old Cubic” and Novotny formulae continue to be pretty much dead-nuts bulleye for me almost every time, only one odd outlier so far out of five batches. My own refract vs. hydro data thus far:
I recently broke out my refractometer to check my double mash beer. I think I’m going to be using it more in the mash because I’m going to start trying 45 min or maybe even shorter mashes.
But it got me thinking, can I use it for determining FG. I don’t care so much about determining exact FG, so much as Terminal Gravity.
I get lost trying to figure out how to compensate or correct for alcohol. If you don’t mind, can you explain it at home brewer user level? And what I would need to do? FYI I have the Brewsor App and Brewers Friend, and an App called Refractometer Calc… Not sure how to use any of them for refractometer correction…
Here’s what I know based on my experience. It will seem lengthy, but if you can digest all of it, it should make good sense I believe.
First and foremost, you need to check calibration of your refractometer with every single use. That’s right – EVERY use. The readings on a refractometer really seem to bounce around a lot each time I use mine. First measure plain distilled water and ensure it reads exactly zero. If it doesn’t, you can either adjust the screw in the thing (I haven’t even done this) or else figure out about how far off it is from zero, then add or subtract that number of points when reading wort. For example, mine often seems to read about negative-0.2 Brix with plain water. So then I dry the thing off, then add a few drops of wort and add +0.2 Brix for an accurate reading. If you don’t check calibration every time and adjust from zero, then the readings are pretty much useless and you’re wasting your time. The next time you use the thing, even just 5 minutes later, check it with water again, because it probably moved! Readings are not stable, that’s been my experience, so I calibrate every single time I’m going to use it. Even check it with water again immediately after measuring wort, and if the readings aren’t the same in water each time, take the average of how far off it is from zero and apply that. So, for example again, if I check in plain water again and now it reads exactly 0.0 Brix, but I got negative-0.2 Brix before, figure I should add the average +0.1 Brix to the reading in wort instead of +0.2. This will provide the utmost accuracy. The more measurements and experience you gain, the more accurate your readings will be.
You must use both your refractometer (recording your readings IN BRIX) and hydrometer together many times with OG readings (zero ABV) along with ANY refract-to-hydro calculator (it does NOT matter which one) such as Sean Terrill’s (Refractometer Calculator « SeanTerrill.com) or Petr Novotny’s (see info in the OP above) so that you can learn the “correction factor” for your specific refractometer. Every refractometer is a little different in this respect. Sean Terrill suggests an average correction factor of 1.04 for many refractometers his cohorts have tested. However, do NOT assume your refractometer’s correction factor is 1.04 without testing it out. Mine definitely has a correction factor of exactly 0.99. I have learned this after measuring the OG of at least 11 batches, and now that I know this correction factor, the results are always extremely consistent and predictable.
Okay… so now let’s say you know your correction factor. You’ve measured several OGs of several different worts, and it’s matching up perfectly with your hydrometer reading every single time. Okay. Now you’re ready to use it for FG readings! Until this point, your FG readings will be a crapshoot! But now that you know how to use the thing and apply the proper correction factor, you can use it for FG. Yay. So to do that… I personally recommend either Petr Novotny’s formulae available from the OP, or use the “Old Cubic” formula which very ironically is available in Excel spreadsheet format from Mr. Sean Terrill at: http://seanterrill.com/wp-content/uploads/2011/04/fg_calculator_v3.0.xls
Check calibration of your refractometer in water as before, then measure your final wort in BRIX, then pump that into Terrill’s spreadsheet but use the result from the column that says “Old Cubic”. That will give you the results you see in the chart above as red squares – almost dead-nuts accuracy. The one goofy data point above, by the way, was where my OG was like 1.098. None of the refractometer calculators are very accurate with high gravity worts of greater than about 1.080 or 1.085. They’ll still work okay for high gravity, but in my experience you’ll probably need to subtract 0.003 or so to match a hydrometer reading.
Note: Hydrometer readings will ALWAYS have the greatest accuracy. Refractometers with good calculators can get you very very close indeed to a hydro reading, within 0.001-0.002, but only that accurate if you follow appropriate standard scientific practice as I’ve attempted to provide in all the guidance above.
I certainly hope this helps somebody more than it causes confusion. It’s working really awesome for me, with my small batches (average 2 gallons). I have a lot of confidence now when using refractometers for FG and ABV that I am getting very accurate results consistent with the more reliable hydrometer readings. So now I don’t need to waste a big hydro sample. Just a few drops and I’m good to go.
It’s really not complicated. Calibration and knowing your correction factor are the keys. Once you’ve got those two things down, you’re golden. Makes more sense to do for small batch brewers too. Love my refractometer. I actually find it a little faster and easier to use, too.
And I have to do none of that with a hydrometer. I can get a hydrometer reading about as quickly as a refractometer reading, especially including all the calibration. I don’t see any reason to not use a hydrometer.
It’s just another thing to nerd out about. Like IBUs and SRMs and LODO and pH and water and… we are all friggin nerds in this hobby to some extent – ain’t we???
