Whenever in the judgment of the board such action will promote honesty and fair dealing in the interest of consumers, the board shall after public hearing promulgate regulations fixing and establishing for any dairy product or class of dairy products a reasonable definition and standard of identity or reasonable standard of quality or fill of container or any combination of such requirements. In prescribing a definition and standard of identity for a dairy product or class of dairy products in which optional ingredients are permitted, the board shall, for the purpose of promoting honesty and fair dealing in the interest of consumers, designate the optional ingredients that shall be named on the label. The definitions and standards promulgated shall conform so far as practicable to the definitions and standards promulgated under the authority of the federal act.