+1 to Sean’s “conversion factors”. I modified the morebeer spreadsheet with his formulas and have found the post fermentation results to be with in a point of the hydrometer reading. I’m pretty much at the point where I use the hydrometer because I have too much beer to rack into a keg and not enough to fill a bottle. I’ll grab a hydrometer reading before I drink it for shits and giggles.
I always drink my hydrometer samples too. It gives me at least a basic idea of where things are at taste-wise.
I tried yours for a batch or two but it gave me similar numbers as the morebeer spreadsheet. I’ll test it again on my latest batch, I haven’t bothered to get a refractometer reading from it post fermentation but I have the rest of the numbers already so it will be easy. I’ll report back.
Based on glastctbrew’s post maybe I’m doing something wrong, I’ll check that too.
When I brew, I boil to gravity, not volume. The refractometer made it easy to get a really quick reading to see where I stood. Now that I’m not using it, I pull a kettle sample (6-8 oz.) with a Pyrex measuring cup and put it in a metal cocktail shaker. I put that in a bowl of ice water and swirl it around. In about 2 minutes, it’s cooled down enough to read. Not quite as fast as a refractometer, but good enough.
If you’re boiling to gravity, however, doesn’t that mean you have to adjust the boil time as you go to account for evaporation until you hit your target?
How big an effect doe that have on the bittering hops or other factors?
I usually boil a timed boil - and hope I hit my volume. I’m not as concerned w/ having my beer be the exact alc. % I was shooting for.
There is so little utilization from bittering hops beyond 60 min. that it really doesn’t matter. For later additions, the gravity reading is crucial to make sure I’m on track and that my 10 min. hops don’t turn into 30 min. hops while I wait for the wort to boil down.
I’m not as concerned about ABV as I am with making sure that my BU:GU ratio ends up where I want it to so that the flavor of the beer isn’t impacted. So I want to be sure I hit my predicted OG as closely as possible.
Ok, here’s what I’ve got. Two carboys with OG 25.5 brix (1.106 according to beersmith, not confirmed with a hydrometer)
Refractometer readings A - 13 and B -12.8 brix.
The different spreadsheets say:
Sean’s: A - 1.0194
B - 1.0172
Notes: There are two different equations in column E for calculating OG from the refractometer reading. version 2.1. One row says 1.106, the rest say 1.107. I used 1.107 for these numbers. The numbers reported are from the “new” column.
morebeer: A - 1.019
B - 1.018
Notes: Spreadsheet calculates OG as 1.108
Beersmith: A - 1.019
B - 1.018
Notes: I’m using the default correction factors, used 1.106 as the OG because that is what beersmith calculates from 25.5 brix.
FG readings with my hydrometer (I double checked calibration) 1.025 and 1.024 after adjusted for temperature. None of them come that close, off by about 5 points across the board. This is similar to what I saw before.
It’s possible there is some user error when I wrote down the OG since I usually don’t write it down right away and I’m sure I didn’t check the temperature of the sample (cooled sample, ATC refractometer). Then again this is the same I saw before. I really do want to do some better controlled experiments some time.
Interesting data Tom. I may also revisit this someday. I also found it difficult to get consistent readings after error correction between my refractometer and hydrometer post fermentation. I have been using my hydrometer mostly because I can trust it but also because I can sample the final product which is important to me. The jury is still out on this one. :-\
I love my refractometer and it’s always within a point or 2 of my hydrometer. If the wort is very hot, be sure and let the sample sit for about 20 seconds, before taking a reading. I find this to be much more accurate. .
Me too. I usually allow the hot wort to sit on the prism with the plastic cover closed for about 15 seconds to cool before taking a reading.
Thanks for the data Tom, your results have me wondering if my adjustment factor for my hydrometer has changed. I haven’t recalibrate it in about 8 months. I’ve got an alt finishing up and the brown I brewed last weekend fermented like crazy and should be done by the weekend. I’ll recalibrate and run FG both ways this weekend and post my results.
Thanks for posting this, Tom. The problem you’re seeing is due to the fact that the OG range used in the initial data set was 8.8-24.3°P, and outside that range the correlation falls off pretty quickly. I’m seeing this with all the very high- and low-gravity data people have sent in. The other major issue I want to address is that I didn’t test any worts with (real) attenuations less than 59%, which I thought was a reasonable floor for typical beers - apparently I was wrong about that, since I’ve gotten several submissions with RDFs in the 40s. There’s going to be a 3.0 release in the next week or two that will hopefully address both issues.
FWIW, the new correlation I’m playing around with (as of now) puts the FGs at:
A: 1.022
B: 1.021
Which still isn’t “good enough” IMO, but it’s getting there. How confident are you in the 25.5°Bx value? If you’d like I could incorporate it into the new dataset.
Also, how did you cool the sample? I’ve noticed that if I don’t chill it in a sealed container evaporation can increase the gravity significantly. It might not explain the discrepancy in the spreadsheet, but I thought it was worth mentioning.
Tom
i ran your numbers through an app i have on my i phone and came up with similar numbers you ended up with on your calcs (1020, and 1019) respectively. very simple to do. i have not gone to a refractometer yet but now that i am down sized to small batches i may. (though thinking of stepping back up to 2-2.5g). the app i think was free, maybe 99cents. don’t know but i am kind of cheap.
if as sean says the higher gravity the correlation is off by just a bit as you experiment (or i do if i am not lazy) we could probably just a secondary correction factor for gravity over 1090 or so…
Worth every penny, IMO. I’ll always have one to brew with.
This is a concern of mine, it was definitely cooled in an open container holding a couple of ounces. I don’t know if evaporation would be enough to throw it off by more than 1 brix, which is what I calculated last night it would need to be off by in order for the other numbers to come in line. I think it would have to lose 10% of its volume and I doubt it loses that much, but maybe it is a combination of evaporation and the initial data range you used to correct the calculation.
I’d say I’m not confident enough in my numbers for you to include them in your data set, but it’s up to you. Like I said, I really need to do some more controlled experiments.
i’ve had the same issue. I now keep a gallon of distilled around so that on brew day i can calibrate it. In fact I had a thermometer fail and didn’t know it until several days after a brew session. So now, I calibrate my thermometer, refractometer and hydrometer every time i use them - annoying, but not as annoying as ruining an entire batch. 
I could calibrate mine for the rest of my life and I still don’t think it would read accurately.
they don’t work in Oregon. only Florida. duh. ;D
Ah, that would explain it!
Maybe it was dropped.