21 CFR §184.1307

1. (a)Ferric sulfate (iron (III) sulfate, Fe2(SO4)3 CAS Reg. No. 10028-22-5) is a yellow substance that may be prepared by oxidizing iron (II) sulfate or by treating ferric oxide or ferric hydroxide with sulfuric acid.
2. (b)The ingredient must be of a purity suitable for its intended use.
3. (c)In accordance with § 184.1(b)(1), the ingredient is used in food as a flavoring agent as defined in § 170.3(o)(12) of this chapter, with no limitation other than current good manufacturing practice.
4. (d)Prior sanctions for this ingredient different from the uses established in this section do not exist or have been waived.