Mich. Comp. Laws § 288.739

Sec. 179. A person shall ensure that a vehicle including a mobile frozen dessert plant used for the transportation of mix, frozen desserts, and their ingredients is constructed and operated so as to protect the contents from heat, sun, and contamination. The vehicle shall be kept clean, and no substance capable of contaminating mix, frozen desserts, and their ingredients shall be transported in the vehicle. Where applicable, a frozen dessert plant shall provide an area for unloading vehicles that can be maintained in a sanitary condition. This area should be surfaced with concrete or blacktop.