(a) Alcohol shall be completely denatured only in accordance with formulas prescribed in this subpart (or in accordance with § 21.5).

(b) Denaturers may be authorized to add a small quantity of an odorant, rust inhibitor, or dye to completely denatured alcohol. Any such addition shall be made only on approval by the appropriate TTB officer. Request for such approval shall be submitted to the appropriate TTB officer.

(c) Odorants or perfume materials may be added to denaturants authorized for completely denatured alcohol in amounts not greater than 1 part to 250, by weight. However, such addition shall not decrease the denaturing value nor change the chemical or physical constants beyond the limits of the specifications for these denaturants as prescribed in subpart E, except as to odor. Proprietors of distilled spirits plants using denaturants to which such odorants or perfume materials have been added shall inform the appropriate TTB officer, in writing, of the names and properties of the odorants or perfume materials so used.

(d) TTB will apply an analytical tolerance of ±5 percent and use standard rounding rules in determining whether completely denatured alcohol complies with the formula prescribed in this subpart (or in accordance with § 21.5).