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Proofing a liqueur.

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Anyone have any suggestions on how to proof a liqueur that has a high sugar content. A normal hydrometer or densitometer won't work because the sugar changes the density. I'm wondering if there's some form of electronic instrument or such that would work for proofing? I can always do a bench distillation, I will have a lab still that I can use for this to satisfy the TTB but I would like something a bit faster and more efficient.

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I take it from your comments that you are familiar with TTB's requirement for determining the obscuration factor that you must use. I think there is no shortcut. For those who don't know how TTB says you must determine obscuration, here are the pertinent section from Part 19 and from the gauging manual.

Sec. 19.376 Determining obscuration.

Proprietors may determine the proof obsecuration as prescribed in 27 CFR Sec. 30.32 of spirits to be bottled on the basis of a representative sample taken: (a) from a storage tank incident to the transfer of the spirits to the processing account, or (B) from a tank after the spirits have been dumped for processing, whether or not combined with other alcoholic ingredients. The obscuration shall be determined after the sample has been reduced to within one degree of the proof at which the spirits will be bottled. Only water may be added to a lot of spirits to be bottled for which the determination of proof obscuration is made from a sample under this section. The proof obscuration for products gauged pursuant to this section shall be frequently verified by testing samples taken from bottling tanks prior to commencement of bottling.

§30.32 Determination of proof obscuration.

(a) General. Proof obscuration of spirits containing more than 400 but not more than 600 milligrams of solids per 100 milliliters shall be determined by one of the following methods. The evaporation method may be used only for spirits in the range of 80-100 degrees at gauge proof.

(B)Evaporation method. Evaporate the water and alcohol from a carefully measured 25 milliliter sample of spirits, dry the residue at 100 degrees centigrade for 30 minutes and then weigh the residue precisely. Multiply the weight of the residue by 4 to determine the weight of solids in 100 milliliters. The resulting weight per 100 milliliters multiplied by 4 will give the obscuration. Experience has shown that 0.1 gram (100 milligrams) of solids per 100 milliliters of spirits in the range of 80-100 degrees proof will obscure the true proof by 0.4 of one degree of proof. For example, if the weight of solids remaining after evaporation of 25 milliliters 0.125 gram, the amount of solids present in 100 milliliters of the spirits is 0.50 gram (4 times 0.125). The obscuration is 4 times 0.50, which is two degrees of proof. This value added to the temperature corrected hydrometer reading will give the true proof.

© Distillation method. Determine the apparent proof and temperature of the sample of spirits and then distill a carefully measured sample in a small laboratory still, and collect a quantity of the distillate, 1 or 2 milliliters less than the original sample. The distillate is adjusted to the original temperature and restored to the original volume by addition of distilled water. The proof of the restored distillate is then determined by use of a precision hydrometer and thermometer in accordance with the provisions of §30.23 to the nearest 0.1 degree of proof. The difference between the proof so determined and the apparent proof of the undistilled sample is the obscuration; or

(d) Pycnometer method. Determine the specific gravity of the undistilled sample, distill and restore the samples as provided in paragraph © of this section and determine the specific gravity of the restored distillate by means of a pycnometer. The specific gravities so obtained will be converted to degrees of proof by interpolation of Table 6 to the nearest 0.1 degree of proof. The difference in proof so obtained is the obscuration.

Note that if you send a sample out for analysis, you want to make sure that it is prepared as required by Part 19.

Good luck.

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Thanks Dave,

I've heard of distilleries using electronic equipment to determine proof and keeping the TTB required equipment on hand. I'll do more research but either way it'll be up to the TTB as to how we determine the proof of our liqueurs.

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