Check My Logic on Refractometer Reading Problems

[tomakana]

OK, I've read through a lot of information on the caveats around using refractometers once fermentation has started (material here as well as in a bunch of other places). I fairly recently began using one, and I'm experiencing something odd that I can't find an explanation for. I think I've narrowed down what's going on, but would appreciate thoughts on my line of reasoning here. If nothing else, this will let me vent a little.

I'm fermenting a wine at the moment (William's Brewing 3-gallon California Cabernet concentrate kit). When I mixed everything up, I took a refractometer reading of 21 Brix/1.083 SG. I realize there are variations in the correlation between brix/SG depending on the exact calculator/scale you use, but this seemed reasonable and the SG was in the range that SG for wines could fall into. Note that I did not do a hydrometer reading to corroborate at this point - but I was confident based on the times I've used the refractometer so far, so didn't want to pull the big sample.

I'm now a couple of weeks into the fermentation - I took a refractometer reading and got 13 Brix, which based on the Northern Brewer calculator put me around 1.030 SG. In my further investigation, nearly every other online calculator I've tried puts me around the same calculated SG with the 21 brix starting point and 13 brix current reading. For a couple of reasons, I was a little suspicious of that - so, I went ahead and took a sample with a hydrometer and got an SG of 1.017, which from what I can tell is pretty far outside the variation that the calculators would usually expect. So, in trying to figure out what's going on, I've take the following steps:

1. Calibrated the refractometer and two floating hydrometers with distilled water and a 1.040 known gravity sugar solution - they all matched readings.
2. Both hydrometers agree with 1.017 on the sample.
3. Took additional readings on new samples of the wine with the refractometer (including the sample used for the hydrometer reading of 1.015) - all of them were consistent at ~13 brix.
4. Sanitized and added a Tilt to the fermentation vessel - it agreed with the 1.017 reading.
5. Experimented with wort correction factors and ranges of brix readings (+/- .5 for the original and new readings) in a variety of calculators to see if there were scenarios that would get me to 1.017. In short, I couldn't really come up with any (more on this in a moment).

At this point, I'm trusting that the wine is ~1.017 SG. The best explanation that I can come up with is that I actually flubbed my initial reading of the refractometer. If I use the calculators back into an initial reading by using my known current SG of 1.017 and refractometer reading of 13 brix, I would have needed an original brix of ~25.5-26. That would have been a starting gravity around 1.110. That's at the high end, if not a little beyond, what wines usually would be, but I managed to find at least one reference on William's site that another of their 3-gallon red kits could go as high as 1.105. So, if it was a little higher sugar than usual and I undershot my dillution to 3 gallons a little, that could be a realistic pre-fermentation SG, I guess. That's what I'm going with at this point.

I guess the moral of the story is to not start your wine-making process late at night, very carefully read your refractometer, and double check the readings at least once before writing them down!

 

[dmtaylor]

Your original Brix might have been off if the concentrate and water were not mixed well enough. I assume you mixed well, but... mentioning this just in case. Regardless, your original Brix reading seems like it must be off by quite a bit. I would also guess it was closer to 26 Brix and 1.100-ish. It had to have been.

Enjoy your 12% ABV semi-sweet Cabernet! I know I would.

 

[Skeeter686]

I think dmtaylor is probably right. I had a similar situation with a beer, where the only thing that seems to make sense is that I didn't mix the wort thoroughly enough after adding some distilled water to adjust the gravity.

 

[tomakana]

Your original Brix might have been off if the concentrate and water were not mixed well enough. I assume you mixed well, but... mentioning this just in case. Regardless, your original Brix reading seems like it must be off by quite a bit. I would also guess it was closer to 26 Brix and 1.100-ish. It had to have been.

Enjoy your 12% ABV semi-sweet Cabernet! I know I would.

Excellent point - I thought I mixed it well, but maybe not. I've only made a couple of wine kits at this point, and that's not a problem I've run into in any of my beers so far, so I'll keep that in mind in the future.

Thanks!

 

[Ramjet]

Did, you calibrate the refractometer for your initial reading? I find mine needs recalibration quite often

 

[dmtaylor]

Did, you calibrate the refractometer for your initial reading? I find mine needs recalibration quite often

I check mine reads zero EVERY TIME I USE IT. It fluctuates a lot, probably based on temperature or who knows why.

 

[jdauria]

What Ranjet said...refractometers need to be calibrated out of the box...make sure it reads zero with distilled water, then you need to take a sample of the wine with the refractometer and with a hydrometer and plug those numbers into a refractometer online calculator to get a "correction factor". Then every time you plug a Brix reading into the online calculator, it applies the correction factor to get you gravity points. I mean you can ballpark using the "4 method"...brix number times 4 = gravity (approximately". In your case 21 Brix x 4 = 1.084 OG, close to your 1.083 but not exact.

 

[tomakana]

Thanks, all - I have calibrated the refractometer to 0 and I recalibrated it when I was worried about the readings - it's pretty consistent so far.

In this specific case, I think it was a mixing issue, which is unfortunately because if I'd realize what the actual reading was, I would have diluted the concentrate a little further. As it is, I hit the yeast's alcohol tolerance pretty early.