FG from Refractometer

[Silver_Is_Money]

You might want to make up some calibration solutions for your refractometer. A 10 Brix/Plato solution is just 10 grams of sucrose (table sugar) in 100 grams of solution, 20 Bx/P is 20 grams in 100 grams.

I added 50 grams of table sugar to 450 grams of room temperature RO water and stirred like crazy. 50 grams sugar in 500 grams total = 10 BRIX.

My refractometer reads this solution at only a wee scant tick below 10 BRIX, and on the SG scale it reads 1.038 to the best of my ability to discern it.

On the Sean Terrill website 9.95 BRIX = 1.0382 SG, so for this single test case case my refractometer actually appears to be reading rather decently along both scales.

 

[doug293cz]

I added 50 grams of table sugar to 450 grams of room temperature RO water and stirred like crazy. 50 grams sugar in 500 grams total = 10 BRIX.

My refractometer reads this solution at only a wee scant tick below 10 BRIX, and on the SG scale it reads 1.038 to the best of my ability to discern it.

On the Sean Terrill website 9.95 BRIX = 1.0382 SG, so for this single test case case my refractometer actually appears to be reading rather decently along both scales.

Looks like your SG scale in the refract has a built in 1.04 wort correction factor. 9.95 Bx => 1.0398 SG [according to: SG=1+(plato/(258.6-((plato/258.2)*227.1))) ], and 9.95 / 1.04 = 9.57 => 1.0382.

Brew on

 

[FunkyMunk]

My issue is that the line on my refractometer is very fuzzy after fermentation has started. Before fermentation the SG and Brix are easily resolved and tend to agree in the lower range (<1.065 or so) but in the presence of alcohol it can be very hard to get a good measure, and the calculators often don't agree with a hydrometer measure. This seems to affect me more with meads and ciders than with beer, but I'm still in the process of getting more consistent measures with each batch.

 

[Morrey]

My issue is that the line on my refractometer is very fuzzy after fermentation has started. Before fermentation the SG and Brix are easily resolved and tend to agree in the lower range (<1.065 or so) but in the presence of alcohol it can be very hard to get a good measure, and the calculators often don't agree with a hydrometer measure. This seems to affect me more with meads and ciders than with beer, but I'm still in the process of getting more consistent measures with each batch.

Yeah, I switch totally to a floating hydrometer once fermentation is underway. The presence of alcohol skews refractometer readings to the point I don't feel my readings (even after online calculation programs) can be totally accurate. Just me I suppose.

 

[seilenos]

My issue is that the line on my refractometer is very fuzzy after fermentation has started. Before fermentation the SG and Brix are easily resolved and tend to agree in the lower range (<1.065 or so) but in the presence of alcohol it can be very hard to get a good measure, and the calculators often don't agree with a hydrometer measure. This seems to affect me more with meads and ciders than with beer, but I'm still in the process of getting more consistent measures with each batch.

I used to get a lot of fuzzy readings, too, but then I changed how I sample.

I use a sanitized "disposable" pipette to pull a small amount of liquid ("disposable" because I am finally having to replace it after about a year of use).
I flip the refractometer lid the whole way open and "paint" from the pipette onto the underside of the lid. A few drops then go on the blue glass side and I close the lid.

Since doing that I get very distinct lines for measurements.

 

[FunkyMunk]

Well, turns out my problem was sediment in the sample. I "cold crashed" it overnight in the fridge and the line was completely clear on the sediment-free sample. I don't see why this would impact the hydrometer reading, but the calculated Brix-to-SG still doesn't match the measured SG; I realize the hydrometer sample may have been inflated due to CO2 in the fermenter, so I plan to measure again with a degassed sample.

 

[Silver_Is_Money]

Well, turns out my problem was sediment in the sample. I "cold crashed" it overnight in the fridge and the line was completely clear on the sediment-free sample. I don't see why this would impact the hydrometer reading, but the calculated Brix-to-SG still doesn't match the measured SG; I realize the hydrometer sample may have been inflated due to CO2 in the fermenter, so I plan to measure again with a degassed sample.

What readings did you get as to OG and FG for both the hydrometer and the refractometer?

 

[FunkyMunk]

What readings did you get as to OG and FG for both the hydrometer and the refractometer?

OG was 1.065 (hydrometer, didn't take refractometer), current SG is 1.024 (hydrometer in bucket), refractometer says 7 Brix. I tried a few different calculators and they all returned a lower SG than what I measured; the highest was 1.010. Both instruments are calibrated, so either my OG measurement was off for some reason (I can compare to what others got using the same juice), my current SG reading is off, or the calculators are wrong (see caveat below). I'm inclined to trust the refractometer: aside from calibrating it just yesterday using the method given earlier in this thread, I can tell by taste that it's higher than 1.010, and 7 Brix seems more likely, taste-wise. I now wish I had taken the initial Brix measurement as well, but I'm picking up another bucket of juice tomorrow (same orchard, supposedly same/similar blend), so can repeat the experiment.

[It just occurred to me that I may need to use a different Wort Correction Factor. I arrived at 1.04 using several samples of unfermented beer wort, and my refractometer seems to correct for this on the SG scale (this is one of those budget Chinese refractometers). I don't have enough data to determine whether it could be different for cider/mead vs. beer, or whether it's a pre- vs. post-fermentation thing. I know enough not to use the SG scale on the refractometer once fermentation has started.]

 

[SoCal-Doug]

Use the refractometer for pre-pitch. Buy a new hydrometer for post-pitch. Work smarter, not harder

 

[Big Monk]

Use the refractometer for pre-pitch. Buy a new hydrometer for post-pitch. Work smarter, not harder

Once you dial in your conversion factor it's much, much easier to use a refractometer for all phases.

 

[sbsmann]

I guess when all is said and done the refractometer looks cool, is easy to use and wastes virtually no liquid. That's all good and cute, but if it can't measure gravity accurately (especially finished gravity) and you have to do all sorts of manual calculations/gyrations to convert (while hoping you didn't make a mistake), it would seem that the $15 hydrometer and a wasted glass of beer is well worth the price to insure you have a completely accurate, trustworthy gravity reading. I don't think I ever messed up a hydrometer reading, but I can definitely see me screwing it up with the refractometer. So I'll continue to play around with it because it does indeed look very cool staring off into the sunset while brewing beer!

 

[cbier60]

Well, turns out my problem was sediment in the sample. I "cold crashed" it overnight in the fridge and the line was completely clear on the sediment-free sample. I don't see why this would impact the hydrometer reading

A lot of sediment can certainly impact the density, and thus the hydrometer reading. A refractometer measures the refractive index of light. A cloudy or non-homogeneous sample refracts light with dispersion; thus, it's not distinct. I pull samples off a port from the bottom of my fermenter, leave them in a glass for 10-15 minutes, and then pull a clear sample with pipette. This usually gives a clear enough line.

I'm inclined to trust the refractometer: aside from calibrating it just yesterday using the method given earlier in this thread, I can tell by taste that it's higher than 1.010, and 7 Brix seems more likely, taste-wise.

Unless your OG was much lower, though, a final Brix reading of 7 corresponds to a pretty low FG, certainly not 1.026

[It just occurred to me that I may need to use a different Wort Correction Factor. I arrived at 1.04 using several samples of unfermented beer wort, and my refractometer seems to correct for this on the SG scale (this is one of those budget Chinese refractometers). I don't have enough data to determine whether it could be different for cider/mead vs. beer, or whether it's a pre- vs. post-fermentation thing.

I don't have any data to back this, but I'd be willing to bet that the correction factor for cider/mead is different (and probably closer to 1). The whole purpose of the CF is to differentiate between sucrose and high levels of maltose; I expect that both cider and mead at least are more sucrose-based.

Use the refractometer for pre-pitch. Buy a new hydrometer for post-pitch. Work smarter, not harder

Ah, the non-believers... Use both for a while to you have confidence that the corrected refractometer measurements are quite accurate.

Once you dial in your conversion factor it's much, much easier to use a refractometer for all phases.

Agreed, as I tried to indicate above.

 

[FunkyMunk]

Got another batch of apple juice, learned a few things in the process:

1) My OG hydrometer reading from the last batch was higher than what others read from the same juice (I read 1.065, others read 1.056). Waiting for a sample to settle in the fridge to see if this could be caused by the massive amounts of sediment.

2) Taking a new reading of the fermenting cider gives a hair above 6 Brix by the refractometer (no sediment) and 1.015 by the hydrometer (with sediment). Still doesn't equate in the calculators, but it's closer than before when taking the real OG into account. May revise after the sample finished crashing. Also planning a similar test with a cyser I have going.

3) The new batch of (unfermented) juice has only a small amount of sediment, and gives me a refractometer reading a hair above 13 Brix, and a hydrometer reading of 1.053, leading to a Wort Correction Index of just about 1. So that's at least one data point.

Unless your OG was much lower, though, a final Brix reading of 7 corresponds to a pretty low FG, certainly not 1.026

Yes, after plugging the real OG into a calculator I've trusted previously, I got a return of 1.013, which seems much more reasonable.

Ah, the non-believers... Use both for a while to you have confidence that the corrected refractometer measurements are quite accurate.

That sounds like a plan. I love the refractometer, since I've started doing a lot of small batches and it's great to only need a drop or so to monitor ongoing fermentations. It's just like any instrument, really, you just need to be calibrated and understand what you're measuring.

Update (10/21/17): I checked the crashed sample, and it's showing 1.007 by the hydrometer and about 5.9 by the refractometer. The huge difference from yesterday's reading suggests that the presence of a lot of sediment in the sample can inflate the hydrometer reading. The new readings still aren't consistent with any of the calculators I tried (Northern Brewer, Brewer's Friend, Beersmith, onebeer.net), even when the option to calibrate the refractometer with a Brix/Wort Correction Factor is present. Basically, I've learned that (at least for non-beer things) the gravity and the Brix aren't easily reconciled once fermentation is underway, and while the refractometer may be useful to get an initial measure and to track the progress of fermentation, the hydrometer is still preferred for determining final gravity and ABV (for now at least, until I have a better way to dial in the conversion). After all that, however, I will ultimately rely on my taste buds to tell me when something is "done".

 

[cbier60]

The new readings still aren't consistent with any of the calculators I tried (Northern Brewer, Brewer's Friend, Beersmith, onebeer.net)... Basically, I've learned that (at least for non-beer things) the gravity and the Brix aren't easily reconciled once fermentation is underway

I don't know if those sites have updated their calculators, but a few years ago, they were all wrong except for the one from Sean Therrill. The one on BS seems pretty closely correlated now, but the others I have no idea about. Sean's was also calibrated for beer only. I have no idea how the refractive properties of other sugars compare to maltose or fructose.