26 U.S.C. § 5381 : US Code - Section 5381: Natural wine

      Natural wine is the product of the juice or must of sound, ripe
    grapes or other sound, ripe fruit, made with such cellar treatment
    as may be authorized under section 5382 and containing not more
    than 21 percent by weight of total solids. Any wine conforming to
    such definition except for having become substandard by reason of
    its condition shall be deemed not to be natural wine, unless the
    condition is corrected.