Section 117A. The commissioner of food and agriculture, in this and the five following sections called the commissioner, may establish and promulgate official grades and standards for farm products, except apples, potatoes and milk, produced within the commonwealth for the purposes of sale, and may from time to time amend or modify such grades and standards. Before establishing, amending or modifying any such grades or standards the commissioner shall hold public hearings in such places within the commonwealth as he shall deem proper. Notice of such hearings shall be advertised in a newspaper or newspapers of general circulation within the county where the hearing is to be held for three successive weeks prior thereto, 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 such farm products, if deemed advisable. The commissioner may determine or design brands or labels for identifying such farm products packed in accordance with official grades and standards established as aforesaid, and may cause to be printed said brands or labels and may dispose of or cause the disposition of the same at reasonable prices. A written application to the commissioner requesting permission to use said brands or labels and a written authorization thereof by the commissioner or a duly authorized assistant shall be a condition precedent to the use of such brands or labels. The commissioner may revoke or suspend the right to use such brands or labels determined as aforesaid whenever it appears on investigation and after a subsequent hearing before said commissioner or authorized assistant that such brands or labels have been used to identify such farm products not in fact conforming to the grade or standard indicated.