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Gravity discrepancy

My gravity into the fermentor did not match up to the gravity in the kettle.

7.47 gal into kettle. I took multiple refractometer measurements here. First was 1.051. 2nd check was off, at 1.048. So I checked a third time and got 1.050. So I stirred the heck out of the kettle wort and took a large sample of approx 8 oz… from that I took multiple additional refractometer measurements, all of which were dead on 1.050. So I attributed original measurements to incomplete stirring after the batch sparge addition into the kettle. Assumed 1.050 to be correct

Post-boil volume 5.5 galons, hit volume dead on. So post boil gravity should have been 1.068.

Instead it was 1.061,

Again multiple measurements, and also verification with the old hydrometer. 1.061.

I filter out hop matter but let the rest of the solids into the fermenter, and this only had 1 oz Warrior bittering so the hop matter made no significant difference in volume.

I’m scratching my head here. Any help?

I’m guessing you were off on the post boil volume. Refractometer OG was confirmed by a hydrometer so that isn’t the issue.

Appreciate the response. But I’m certain that I have 5.5g in the fermentor. It’s got a mark on it, the same one I always use to assess volume.

I also double checked the volume pre-boil too. I measure height of the liquid in kettle and have a conversion for height: volume of 3.21 cm/gal. So I am also pretty certain that volume was also correct.

Oh and here’s one other little tid-bit of info, that makes this even more confounding:

15 minutes before the end of the boil I took a refractometer reading to judge how close I was to being done, expecting an end-point of 1.068, and I got a reading of 1.066. Only took that reading once, because I thought it was in keeping with what I was expecting.

So how the $*@# do I go DOWN in gravity into the fermenter?!

I’m telling you, if I were reading this I would just chalk it up to “this bozo doesn’t know what he’s doing” and move on. But seriously, I took so many readings and made careful measurement of volume too.


Oh well, it will be beer.

I only have a hydro and when I take my readings I always need to adjust for the hot wort temp…is that not the case for the refract?

sorry if this is a dumb question?

I agree, the arithmetic says that 7.47 gal of 1.050 wort, boiled down to 5.5 gal will have a specific gravity of 1.068.

If no one slipped in while you were busy and stole some sugar, and if the measurements are correct, the gravity should be 1.068.

I’m assuming you took multiple gravity readings to confirm the post-boil gravity and double-checked the volume - the markings on two of my kettles are not accurate so I’ve had to re-mark them. Did you get the same reading with both the refractometer and the hydrometer post-boil? Was the sample in the hydrometer cooled to the calibration temp marked on the hydrometer? Have you calibrated the refractometer with distilled water at the calibration temp - apparently, the paper can slip?

If re-checking and re-re-checking doesn’t reveal a measurement error, the only thing that I can GUESS might be going on is that even after your pre-boil stirring the wort may not have been evenly mixed. That could have given you an 8-ounce sample that was not representative of the actual pre-boil gravity.

But, you have beer; so the day wasn’t a total loss!

Yeah I calibrated the refractometer to water. I have R.O. water on hand I figure that is close enough to distilled water.

The hydrometer checked out as well (actually about 0.002 off but I am correcting for that in this discussion).

Yeah I wasn’t sure about teh volulme markers either. I get my kettle volume by using old fashioned geometry (πr2) x h. So I know that for my kettle each gal is 3.21 cm in height.

The fermentor (a BetterBottle) is marked by me, and has been used countless times before with expected results.

And no spills or unexpected volume losses.

if you are 100% sure the equipment is correct and 100% sure the readings are correct and 100% the math is correct: the problem has to be in the volume measurements. Either the 7.47 is off or the 5.5 is off. Which is where I’d put my wager.

The mathematical answer probably assumes 100% wort…no particulates and no sediment.


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