26 USC 5387 - Agricultural wines

(a) In general 
Wines made from agricultural products other than the juice of fruit shall be made in accordance with good commercial practice as may be prescribed by the Secretary by regulations. Wines made in accordance with such regulations shall be classed as standard agricultural wines. Wines made under this section may be cellar treated under the provisions of section 5382 (a) and (c).
(b) Limitations 
No wine spirits may be added to wines produced under this section, nor shall any coloring material or herbs or other flavoring material (except hops in the case of honey wine) be used in their production.
(c) Restriction on blending 
Wines from different agricultural commodities shall not be blended together.