Cal. Food & Agric. Code § 38181

Skim milk, nonfat milk, or fat-free milk is the product that results from the complete or partial removal of milk fat from milk. It shall contain not more than twenty hundredths of 1 percent of milk fat and not less than 9 percent of milk solids not fat, except that milk produced and marketed pursuant to Article 7 (commencing with Section 35921) of Chapter 2 of Part 2 of this division as skim milk shall contain not more than twenty hundredths of 1 percent of milk fat and not less than 8.5 percent of milk solids not fat.