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Comparaison entre le taux d'alcoolémie indiqué sur l'étiquette commerciale et le taux d'alcoolémie réel mesuré
Bit of a random question!
I have just got a hold of a DMA35N as I was “playing” with a new piece of equipment, I was measuring the abv of a few large commercial brand gins and vodkas. I was surprised to see that most of the bottles tested were around 1%abv below the label. Is this a calibration issue of my DMA35 or is it normal for the abv to be slightly below the label over time?!
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8 Réponses
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You can’t use that for your final proof for a reason. Ours also tends to be about one proof degree off of our readings when using approved hydrometers and thermometers – especially when the temperature of the spirit is ~5F off of 60F either way. The DMA’s temp correction is pretty good, but not perfect. I have, however, done the same thing, and noticed a couple products that are over 10 proof degrees off. That was clearly a proofing error on the side of the distillery.
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Before the recent change in proof variation I spoke with a distiller who would run Smirnoff 100 proof through his TTB approved benchtop machine from Anton Paar because it would always come out precisely at the lowest point of the allowable tolerance which at the time I believe was 49.85% ABV. It would not surprise me if there are other large distillers were doing the same thing but 1% under is obviously outside the expanded 0.3% tolerance so there is a calibration issue or some are cheating the expanded tolerance.
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@EZdrinking I wonder what that .15% per bottle translates to the Smirnoff bottom line per year.
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Smirnoff sells roughly 230.4 million liters/year if my math is right that could mean they would save as much as 691k liters in alcohol per year.
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The DMA 35N was the second handheld density meter launched by Anton Paar in the 90’s. It is a bit old and likely needs a calibration adjustment. You can do this using distilled water. Do you need a user manual?
The finished vodka may contain some flavors or sweetener. The density of these materials act like water and show up as a dilution of the sample causing them to read below the label claim. The heart cut from your still should be just ethanol and water which should agree between the hydrometer and DMA 35N. Results on the DMA 35N, as with all DMA 35’s after this model, can display results of %ABV at 20 C or Proof at 60 F. When comparing the results, make sure the temperature conversions are correctly compared. The DMA 35 series use a factor called the “Temperature Coefficient” to convert the density of the sample at ambient temperatures to the correct result at 20 C or 60 F. The Temperature Coefficient for calculation is likely to have changed. The user manual shows the steps for changing this Temperature Coefficient within the meter.
Start with the distilled water check procedure. If the water check is accurate, then the Temperature Coefficient can be adjusted to provide better results that are closer to your hydrometer.
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Wow, Thats for the great reply, I have done the calibration in water. Perhaps I need to dig a little deeper into the temperature coefficient. The unit has just come back from a service so i beleive that its working correct just needs some factor of correction.Thanks
Dan
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@dmacnz Just checking back in here… I found that the best recalibration I could do was selecting the “factory adjustment” tab under “adjustments”. My water calibration wasn’t doing the trick, I must have had bad technique or was doing something wrong. Selecting the factory adjustment now has it back to agreeing with our approved hydrometers and thermometers.
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These are almost certainly maintenance and adjustment issues. First rinse the cell with a warm 1% caustic such as Alconox (amazon) and let it set 3-5 min then flush thoroughly with distilled water (grocery store) ….and then flush again and again. Wait at least an hour, then perform a water check. If fails, try again. If you are certain the cell is clean, follow the prompts to perform an adjustment. Run a major brand stripped vodka and should be very close. Triple Platinum is sold everywhere, I believe, and will measure 40.00 %v/v (using Ethanol AOAC @ 60 K method).
Run water checks daily (min). You should only need to adjust the instrument (with distilled water) a few times/yr (which is why many stop checking).
My DMA has been hit by a forklift and traveled many miles in my truck bed and always measures right-on. I use many of our customer’s brands basically as standards. They almost all bottle at slightly different proofs, but they are always the same, or will be on a properly maintained DMA.
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