The proprietor must gauge spirits, wine, and alcoholic flavoring materials when required to do so by the appropriate TTB officer or when the spirits, wine, or flavoring materials are:

(a) Produced and entered for deposit;

(b) Filled into packages from storage tanks;

(c) Transferred or received in bond;

(d) Transferred between operational accounts;

(e) Mixed in the manufacture of a distilled spirits product;

(f) Mingled under §19.329;

(g) Reduced in proof before bottling;

(h) Voluntarily destroyed;

(i) Removed or withdrawn from bond;

(j) Tax determined;

(k) Returned to bond; or

(l) Denatured.

(26 U.S.C. 5204, 5559)