Market milk shall be cooled as indicated by a recording thermometer to 50 degrees Fahrenheit (10 degrees Celsius) or less within four hours of the commencement of the first milking and to 45 degrees Fahrenheit (7 degrees Celsius) or less within two hours of the completion of milking. The blend temperature after the first milking and subsequent milkings, or milk in transit on bulk milk tankers, shall not exceed 50 degrees Fahrenheit (10 degrees Celsius). The secretary may promulgate regulations to provide for temporary deviations from the requirements of this section that may occur as a result of emergencies arising from equipment failure, or as a result of other unusual circumstances; provided, however, that the quality and safety of the product are not adversely affected.