Before refusing to grant or renew, or before suspending, revoking or refusing to transfer, a license, the Commissioner of Agriculture shall afford the applicant or licensee an opportunity to be heard before him or his designated agent. A citation shall be directed to such applicant or licensee by registered or certified mail to his last-known address, giving at least five days’ notice of such hearing and a statement of the matters complained of. After such hearing and upon entry of any ruling thereon, the commissioner shall forthwith serve a certified copy of such ruling upon the applicant or licensee at his place of business or by registered or certified mail to his last-known address. The original, and a statement in writing of the findings of fact in support thereof, shall be filed in the office of the commissioner.