Market milk, at the time of delivery to the consumer, shall contain not less than 3.5 percent of milk fat and not less than 8.7 percent solids not fat. The minimum percentages of milk fats and solids not fat required by this section may vary by an amount no greater than 0.1 of 1 percent, provided that the total combined percentages of milkfat and solids not fat, at the time of delivery to the consumer, shall equal or exceed 12.2 percent.