27 CFR §19.144

The proprietor may temporarily extend or curtail the distilled spirits plant premises for alternate use with the premises of a contiguous volatile fruit-flavor concentrate plant. If a proprietor wishes to use all or a portion of the premises alternately as a volatile fruit-flavor concentrate plant or vice versa, the proprietor must comply with the requirements of §§ 18.39 and 18.41 through 18.43 of this chapter.