I've been noticing some variations in my bottling runs, and I'm trying to track down the source of the issue, or at least a solution.
On a recent bottling run, I bottled 1080 750ml bottles, which i had gauged at 80.0 at the weight of 1674.8 # at a temp of 73.54 deg F. According to alcodens I should have bottled 1072 bottles. So I went over 8 bottles. I do volume checks throughout the run (8 or so on a run this size) on a regular graduated cylinder (+/-2ml at 20c), and it tends to be about a wash in over/under 748-752ml, to be this off over that size bottling run I would have to under fill 11 ml on every bottle. I gauge multiple times as well and fall within the acceptable range.
I use alcodens for my proof and volume corrections, I have a calibrated scale, my hydrometer is calibrated (+.18 proof at 80deg at 60F), as is my thermometer (calibrated to every 5 degF). It's been a year since my last scale calibration, but that tends to be off by tenths of a lb not 12.4 lbs. I run my gauges on weight not volume throughout the operation, until bottling.
Any thoughts? I'm thinking I need a calibrated 750ml cylinder to check my bottles? Any other tips on getting this right?
Use weight for your bottle fill instead of volume. Weight doesn't change, but volume does with temperature.
As bluefish says, use weight. For your calculation the only volume you should put into alcodens is 750 mL and the only temperature is 60 f (assuming you are TTB)
Also, do not bother measuring the temperature of your bulk spirit. With mass that is irrelevant, and it has confused you because you have put that 73.54 f into Alcodens to calculate the 1072 bottles. 1674.8 lbs should have filled only 1066 bottles at 60 f. You have actually filled 14 more bottles than you should.
What you have done is filled the bottles with 750 mL of spirit at 73.54 f instead of at 60 f. There will be less than 750 mL in the bottle which is part of the reason you ended up with extra bottles.
Also, throw away that measuring cylinder. For one thing it is calibrated at 20c not 60f. (was the 80 proof you measured at 20 c? ) Parallel sided glass cylinders are not sensitive enough to read to fractions of a mL unless they are very skinny. Even so, I still can't see how your measuring cylinder was 11 mL out.
Don't do your volume checks with a measuring cylinder, use weight.
750 mL of 80 proof at standard temperature (US) 60f weighs 712.34g. (in air for TTB calculations only)
An easy way I use is to stack say 10 cases of empty bottles with caps on your scale. Fill them all then re-weigh.
If they are cases of 6 X 750 mL then the lot should weigh 60 X 712.34 = 47.74 Kg (94.226 lbs) more than when they were empty
Your 1674.8 lbs of 80 proof will give you 804.1 liters at 73.54°F. AlcoDens and the TTB Tables agree on this. But because 750 ml at 60°F grows to 754 ml at 73.54°F you should expect to get 804.1/0.754 = 1066 bottles. This agrees with PeteB’s mass based calculation. The underfill is 4 ml per bottle so you could expect to have 1066 x 4 / 750 = 5.7 extra bottles. The fact that you had 14 too many means that we still need to find where the extra 8 bottles came from.
I agree that your scale is unlikely to be the source of error, but keep it in mind to check once you have eliminated all other possible reasons.
If your proofing was out and the 1674.8 lbs actually gave you 810.0 liters ( = 1080 x 0.750) instead of the calculated 804.1 then your density at 73.54°F was 7.8262 lb/WG and this would correspond to a proof of 88.2. It is unlikely that you could be this far out.
Another possibility for error would be if your bottling temperature was not the 73.54°F in your storage tank. But the temperature would need to be in the region of 90°F to explain the difference. This should be easy to check.
As PeteB has said, it would be better to do your quantity checks during the run based on mass rather than volume. If you have an accurate lab scale you could also use it to calibrate your measuring cylinder. Use AlcoDens to calculate the expected weight of 0 proof (i.e. water) when your cylinder is full, and fill it with RO or well filtered water.
If you have a bottling machine that uses a fixed head (pressure) and adjustable timer to control the fill quantity then you can set it to give a target weight rather than volume. The weight filled will vary with the temperature of the spirit and if you make a note of the time required and the temperature each time you adjust it you will soon be able to draw up a calibration curve to speed up the job.
Racked my brain the other day about how I could have possibly overfilled by 17ml, or had such a significant proofing error (on a smaller bottling run). Checked bottle weights - spot on. Dumped bottles to check proof, spot on. Nothing wrong. Counted the cases over and over, checked the bottles. Checked the hydrometer. Nothing wrong.
Turned out a full case ended up stacked on a pallet of empties, and the total count was 6 bottles short. Racked my brains for a day until my brother comes over and asks why a full case was sitting on top of a pallet of empties. Hallelujah, all of the sudden the math works, all is right in the world.
Any chance you over counted by 1 case, or a case of empties made it over to the full pallet side? Just throwing it out there.
Everything PeteB and Meerkat say still applies. Dump the graduated cylinder - get a small scale with reasonable accuracy to check bottle fill. I have a small 5kg scale with good sub-gram accuracy.
Thank you all for your input, this was very helpful. I weighed four cases empty (with caps and labels) and full, and came up about .5lbs short. That would translate to about 5ml short per bottle, which makes sense if I was checking volume at 750ml but at 73 degrees instead of 60, and in a graduated cylinder that is +/- 2ml at 20c. Across 1066 bottles that would yield about 7 bottles short.
To Silk City's comment, I have a feeling you may be onto something. At the end of the run I had affixed 89 labels, but there were 90 cases stacked, which i assumed meant we had just missed a case label on one case, but now I'm wondering if we accidently stacked 1 empty case in the filled bottles. Which means... restack 90 cases to check and see. I'm also going to go back and weigh 10 cases to get a better sample.
It's funny that I've been checking fill runs on volume all this time, when the whole rest of my operation has run on mass. I had the NCDA out this morning to check the scales, they were over about .2 lbs on 500 lbs, so sitting pretty close there. I'll calibrate my lab scale and use it for fill checks, got a bottling run coming up this friday.