27 CFR § 25.281 - General.
(a) Reasons for refund or adjustment of tax or relief from liability. The tax paid by a brewer on beer produced in the United States may be refunded, or adjusted on the tax return (without interest) or, if the tax has not been paid, the brewer may be relieved of liability for the tax on:
(c) Rate of tax. Brewers who have filed the notice required by § 25.167 and who have paid the tax on beer at the reduced rate of tax shall make claims for refund or relief of tax, or adjustments on the tax return, based upon the lower rate of tax. However, a brewer may make adjustments or claims for refund or relief of tax based on the higher rate of tax if the brewer can establish to the satisfaction of the appropriate TTB officer that the tax was paid or determined at the higher rate of tax.