The commissioner, with the approval of the Board of Agriculture and Industries, may establish and promulgate official grades and standards for farm products and fish produced and processed within the state for the purpose of sale and may from time to time amend or modify such grades and standards. Such official grades and standards may be promulgated so as to apply regardless of the stage of processing or of the form in which such farm products and fish are sold. Before establishing, amending or modifying any such grades or standards, the said commissioner shall hold public hearings in such places within the state as shall be most convenient to producers of the commodity under consideration. Notice of such hearings shall be advertised for three successive weeks prior thereto in a newspaper or newspapers of general circulation within the county where the hearing is to be held and shall specify the date and place of each hearing and that it is to be held for the purpose of obtaining information with a view to establishing grades or standards for farm products and fish.