[glastctbrew]

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.

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.

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.

[a10t2]

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.

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.

[weithman5]

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.. 

[maxieboy]

Worth every penny, IMO. I'll always have one to brew with.

[tschmidlin]

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.

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.

[jrlooney]

I loved my refractometer when it worked.  For some reason, it started deviating from my hydrometer so I stopped using it.

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.   

[denny]

I could calibrate mine for the rest of my life and I still don't think it would read accurately.

[blatz]

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.

[denny]

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.

Ah, _that_ would explain it! 

[ccarlson]

Maybe it was dropped.

[denny]

Maybe it was dropped.

Well, it started out working fine for a couple years and I haven't dropped it.

[tschmidlin]

Maybe it was dropped.

Well, it started out working fine for a couple years and I haven't dropped it.

Maybe it was Studach who dropped it 

[Pinski]

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.

Something told me I should hold off on that purchase. Must be the vortex throws them off.

[blatz]

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.

Something told me I should hold off on that purchase. Must be the vortex throws them off.

guess I will throw my 2 pennies in - since I initially calibrated my refractometer to my hydro about 2 years ago and through data found my correct adjustment factor in the refracto tool in Beersmith, I have never had a problem with it - its always dead on, even for post fermentation readings (which I always take a hydro of since I like to taste).

Its most helpful to me for determining the gravity along the boil so I can know where I stand as far as extraction from the mash.

YMMV.

[ccarlson]

I wouldn't give up on them. It one of the best brewing investments I ever made and I paid a lot more for mine than they are going for now.