# proof obscuration

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When determining proof when a spirit has in excess of 400 mg/l obscuration are you required to follow this method or can you simply distill and proof using a lab still? Video referenced is determining proof obscuration by evaporation.

Thanks,

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Per the recent TTB webinar:

Methods to find proof:

True proof by distillation

- any sample, regardless of proof or solids content

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• 2 weeks later...

The applicable section of the regulations appears, in passing, in the video to which you link. It is 27 CFR 30.32.

§ 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.

( 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 §13.23 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.

(Sec. 201, Pub. L. 85–859, 72 Stat. 1358, as amended (26 U.S.C. 5204))

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• 3 weeks later...

What things would be typically near the 400 range?

Are any oils or other things that come over in distillation ever considered 'solids', such as those found in a gin or a vapor infused flavored vodka?

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What things would be typically near the 400 range?

Example - Canadian whiskeys made with a blending agent and sugar. Certain cocktails.

Are any oils or other things that come over in distillation ever considered 'solids', such as those found in a gin or a vapor infused flavored vodka ?

No. How can I say this with assurance when I'm certainly no chemist? Consider this - one acceptable way you can determine the obscuration is by distillation:

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 §13.23 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

So, that means obscuration is the solids left behind when you redistill = it is also anything left behind when you originally distill = it is never present in gin, vodka, whiskey, brandy or anything that contains only the vapors that come into the spirits through distillation.

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Thanks Dave, that is what I was thinking, but when you say it that way, it makes total sense...

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• 2 weeks later...

Thank you - to everybody and sorry for the delay. One last question, for those that need to distill are we using this Kjeldahl 2 unit or equivalent, the Velp Kjeldahl, or a different setup for liqueurs?

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• 2 years later...

My question is what about liquor with sugar added between 0-400mg/100ml?

Does TTB ignore the obscuration up this point.

If it is 0.4 degrees obscuration of proof per 100g/100ml it seems like that is a lot of allowable error.

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• 1 year later...

@Still_HollerSorry to drag up such an old thread, but I was grappling with this recently and came upon this thread while searching for the answer.  I believe I have found the answer in 27 CFR 30.71.. See also 30.72.

§ 30.71 Optional method for determination of proof for spirits containing solids of 400 milligrams or less per 100 milliliters.

The proof of spirits shall be determined to the nearest tenth degree which shall be the proof used in determining the proof gallons and all fractional parts thereof to the nearest tenth proof gallon. The proof of spirits containing solids of 400 milligrams or less per 100 milliliters shall be determined by the use of a hydrometer and a thermometer in accordance with the provisions of § 30.23. However, notwithstanding the provisions of § 30.31, the proprietor may, at his option, add to the proof so determined the obscuration determined as prescribed in § 30.32.

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