Cal. Food & Agric. Code § 41161

In order to prevent fraud and deception in any transaction which involves fresh grapes for wine and byproducts purposes, that requires the extraction or pressing out of the juice, in which the average percentage of soluble solids in the juice of such grapes is the basis for the amount of the purchase price, the determination of such average percentage of soluble solids shall be made by the commissioner or his deputies or his inspectors.